Candy
05-01-07, 06:06 AM
This is a thread copied from our old forum. It has some very useful information if you are interested in number conversions.
Gulf Diver wrote:
The purpose of this posting is to inform all interested in reef coordinates and coordinate conversion as to the many variables that are involved, and one conversion method that works for me.
Reef Coordinates, whether for an artificial or natural reef are typically in one of two formats. The two formats are Loran C and GPS (including DGPS and WAAS). The original position format reference used should be identified. Such as, an artificial reef that was put down with a Loran C reference, or one that is put down with a GPS reference. The original reference for the reef is the most accurate location information for either locating with the same reference equipment or converting to another reference standard. Converted coordinates should be identified as such.
Loran C---position coordinates are given in a set of TD’s (Time Differentials), which are generally called TD1 and TD2. Loran C is a land-based system that uses a set of transmit stations and your loran receiver to approximate your receivers position. This system is subject to variances due to land mass distortions. To compensate for these distortions, most Loran C receivers have an AFS function, which normally is defaulted to be On. Additionally, Loran C receivers can be set up to give position coordinates in latitude and longitude.
GPS---position coordinates are given in latitude and longitude. GPS is a satellite-based system that uses a number of satellites and your GPS receiver to approximate your receiver’s position. This system is not subject to the land mass variances like the Loran C system. It is subject to SA (selective availability), which intentionally transmitted errors to degrade the precision of position finding. SA errors are not currently being transmitted, but can be if the needed to degrade the GPS system. DGPS originated due to SA, and includes the use of additional land based transmitters and a differential beacon receiver interfaced with your GPS receiver. DGPS would remove the bulk of the errors to provide more precision over GPS with SA enabled. WAAS is the newest GPS format that is available and was established initially for aircraft use. It uses correction information that is imbedded in the satellite transmissions. For all practical purposes, without SA errors being transmitted, GPS, DGPS and WASS enabled GPS will all provide a very accurate position in latitude and longitude. Additionally, GPS receivers can be set to give position coordinated in TD’s.
Next, if both Loran C and GPS receivers can provide position coordinates in both TD’s or Latitude and Longitude, then it shouldn’t be a problem to convert from one format to another. Wrong…….. Equipment from different manufactures all produce different results when converting from one format to another. Before looking at how to convert formats, let’s consider a few more of the variables with the actual reported reef locations.
Accuracy of the reported location. Generally, the GPS (including DGPS and WASS) reported locations are very accurate, and can be located regardless of what brand of GPS that you have. Loran C on the other hand, will vary slightly from one brand to another in calibration and the actual TD’s that they produce for the same location. This variance is normally very slight. Was the same Loran C used for all of the reef deployments over the years for your area? Probably not. How did the reported location originate? Did the Tug Captain push save on his Loran C unit when the end loader pushed concrete culvert off of a 200 ft long barge? Did the end loader operator push save on his GPS when he pushed the reef material overboard? Was the tug/barge anchored or drifting during reef material deployment? Did the reported location originate when a boat observed the reef material on its bottom machine? If so, what kind of transducer was used (20, 8, or 6 degree cone)? The most accurate reported location would be with a boat observing the material with a 6 or 8 degree transducer. Also consider the reef size. The larger the target, the easier it should be to locate part of it.
Converting Formats----Most of us are interested in accurately converting from Loran C TD’s to latitude and longitude for use with GPS units. Most reefs deployed prior to 1998 were put down with a Loran C reference. So how do you do the conversion? You find a conversion system that provides the desired accuracy and repeatable accuracy. You can just about be assured that the Loran TD’s for various reefs came from different Loran receivers. You can establish a fixed method of conversion and stick with it. Converting some TD’s to lat/long on your Loran unit, some on your fixed GPS, and some on your handheld GPS will not provide accuracy and repeatability. Also, remember the AFS function of Loran to overcome land mass distortions. The TD’s that you want to convert were probably obtained with AFS enabled. I recommend converting TD’s to Lat/Long with a computer program that also addresses AFS.
1. Select a conversion program that addresses AFS. Select your GPS unit. I use the Loran & GPS Vault program to convert all my TD’s. I use a Megellan 6500 GPS unit with a Magellan DBR-IV differential beacon receiver.
2. Convert from TD’s to Lat/Long. Use your program to convert Loran TD’s to Lat/Long and make sure the AFS function is enabled.
3. Locate and save reef location with your GPS. Use converted coordinate and drop a buoy on the position. Use an expanding circular search to locate the reef and save the actual location. I find that my conversion with the correction factor applied generally holds accurate for the longitude. A north / south search is what I typically need to do to locate the reef.
4. Compare your conversion to the actual GPS Lat/Long. How close is the conversion?
5. Note the difference for a half dozen to dozen of sites. Does the difference remain relatively constant?
6. Average the difference and use it as a correction factor. Throw out the extreme positive and negative differences and average the remaining differences.
7. Add or subtract this correction factor to your conversion for an estimated Lat/Long. I have been using this method and it proves to hold pretty accurate over the entire local area (Offshore Destin), and even works for the Pensacola area with the same correction factor. I subtract 0.030 from both the converted latitude and longitude. I call my conversion with the correction factor the DE (Differential Estimated) location.
The Loran & GPS Vault program is available through:
http://www.worldwidewaypoints.com/
There are many other programs available for your coordinate conversions.
Here is a sample of some of my conversions:
Barrel Barge / DE—N30.21.795, W86.36.097 / DGPS----N30.21.824, W86.36.091
Butler Barge / DE---N30.21.516, W86.35.621 / DGPS----N30.21.523, W86.35.621
AF Barge / DE---N30.21.253, W86.29.578 / DGPS----N30.21.249, W86.29.587
Lost Barge / DE---N30.17.904, W86.27.372 / DGPS----N30.17.894, W86.27.383
Miss Louis / DE---N30.22.294, W86.25.314 / DGPS----N30.22.287, W86.25.317
Good luck on your conversions.
I welcome any comments on conversion methods.
JT
Grand Admiral
1008 Posts
Posted - 03/17/2003 : 7:33:20 PM
This is taken from the Garmin website for those interested in what WAAS is.
You've heard the term WAAS, seen it on packaging and ads for Garmin products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.
The origins of WAAS
The Federal Aviation Administration (FAA) and the Department of Transportation (DOT) are developing the WAAS program for use in precision flight approaches. Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity, and availability. WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing, and satellite orbit errors, and it provides vital integrity information regarding the health of each GPS satellite. Although WAAS has not yet been approved for aviation, the system is available for civilian use such as boaters and recreational GPS users.
How it Works
WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.
Who benefits from WAAS?
Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of WAAS is that it does not require additional receiving equipment, while DGPS does.
Other governments are developing similar satellite-based differential systems. In Asia, it's the Japanese Multi-Functional Satellite Augmentation System (MSAS), while Europe has the Euro Geostationary Navigation Overlay Service (EGNOS). Eventually, GPS users around the world will have access to precise position data using these and other compatible systems.
100 meters: Accuracy of the original GPS system, which was subject to accuracy degradation under the government-imposed Selective Availability (SA) program.
15 meters: Typical GPS position accuracy without SA.
3-5 meters: Typical differential GPS (DGPS) position accuracy.
< 3 meters: Typical WAAS position accuracy.
JT
Grand Admiral
1008 Posts
Posted - 03/20/2003 : 09:38:17 AM
The nomenclature that I am going to use on each reef is:
Coordinates Confirmed -- This means someone has posted good numbers that are different from the posted numbers
+Coordinates VERIFIED+ -- This means someone posted WAAS or DGPS numbers that matched the posted numbers, or two people have posted almost identical numbers.
JT
Grand Admiral
1008 Posts
Posted - 03/20/2003 : 10:15:04 AM
I also want to note that my numbers, as well as other posted on here, may not line up with others because of bottom machine configurations. For starters, no one's transducer is perfectly aimed to show the bottom directly under the boat. I know for a fact that mine is picking up objects slightly in front of my boat at 80 feet deep. You also have to consider that if the boat is not perfectly level and there are waves, then the beam will be varying because of that as well.
So, while the numbers posted may not be *perfect* coordinates, they should be able to get you close enough that you should have no problem finding the reefs.
tjl
Ensign
29 Posts
Posted - 04/05/2003 : 10:27:43 AM
Hmmm... technical difficulties . Just drafted a reply to this and, poof, it's gone. Oh well... here's another try.
First, I really appreciate the time and effort you guys put into this thread--it's great info.
Then, I wonder what you think of this take. I normally use my GPS in the map view. When zooming down to 3 meters the boat pretty much covers the screen. So, when trying to find a site (converted by either the Andren s/w or my Garmin GPS, which seem to use about the same algorythm) I zoom out to 120 feet. That gives better perspective of boat movement/turning in relation to the target. I haven't tried to find any culverts with WAAS yet, but since most of our sites are substantially larger than 3 meters, I find WAAS less meaningful than expected.
Let me know if my 'plain farmer' approach holds water from your view.
Cheers, tj
tjl
Ensign
29 Posts
Posted - 04/05/2003 : 10:33:14 AM
Whoops, my cranial spellchecker says that's 'algorithm'
gulfdiver
Grand Admiral
944 Posts
Posted - 04/08/2003 : 12:28:38 PM
tjl--sounds like you have refined the area search by using your GPS in map view. As far as your conversions from TD's to Lat/Long go, does both your GPS and Adren s/w provide the same conversion? Do you use a correction factor to further refine the converted numbers? Are your conversions with or without a corection factor pretty accurate throughout the entire area? Snake166 informed me that he converts with his GPS and then applies a correction factor for his conversions.
Edited by - gulfdiver on 04/08/2003 12:31:12 PM
tjl
Ensign
29 Posts
Posted - 04/09/2003 : 1:58:13 PM
The GPS and Andren have been identical in the few times I've compared them. I never heard of the conversion factor before reading yr posts.
tj
n/a
deleted
111 Posts
Posted - 07/05/2003 : 09:06:50 AM
There's a lot of, for lack of a better word, error built into any conversion from LORAN to GPS/DGPS. A lot of information can be found at this site
http://pollux.nss.nima.mil/index/index.html
n/a
deleted
111 Posts
Posted - 07/05/2003 : 09:41:25 AM
Theres a lot of info on LORAN and GPS/DGPS at this site.
http://www.floridaconservation.org/marine/lorangpsdgps.htm
n/a
deleted
111 Posts
Posted - 07/08/2003 : 4:49:47 PM
Question time. Two friends of mine (one a diver) that gave up fishing/diving/boating gave their location books to me. I copied them, and gave them back in case they decide to get back into this madness again. Almost all coordinates are LORAN numbers. My question is, should I post them a few at a time, or not. Some seem to be almost to Panama City, and some to Pensacola. And, some are way off shore (at least they seem to be). I'm not an avid fan of converting these numbers to GPS. Here's one that was listed as "Good", 13711.5 47114.9, or one listed as "Rock", 13480.4 46977.0. And, one that was listed as "Junk", but it also said that there were Red Snapper, Triggerfish, Scamp, Flounder, and Grouper there. If these are repeats of previously listed sites, sorry. Now, should I start posting or not?
tjl
Ensign
29 Posts
Posted - 07/08/2003 : 9:02:51 PM
Nice--thanks
tj
quote:
Originally posted by retafe7
[br]Theres a lot of info on LORAN and GPS/DGPS at this site.
http://www.floridaconservation.org/marine/lorangpsdgps.htm
gulfdiver
Grand Admiral
944 Posts
Posted - 07/08/2003 : 10:28:57 PM
retafe7---Please post any td's or lat/long coordinates that you want to post. The more the better. Loran Td's are OK to post. I have very good success in converting these to lat/long coordinates. I used to search for TD's with my loran unit, but have since refined converting the coordinates to lat/long that I now typically convert and locate with my DGPS unit. Your above TD's convert to: Good--(13711.5 & 47114.9) N30.18.345 and W86.29.825; Rock (13480.4 & 46977.0) N29.55.194 and 86.48.515. Please post away.
JT
Grand Admiral
1008 Posts
Posted - 07/09/2003 : 09:01:48 AM
Go ahead and post them, but please do so in the "Non Published Reef" Topic
Thanks,
~JT
n/a
deleted
111 Posts
Posted - 07/26/2003 : 7:57:39 PM
I almost forgot that I had saved this bit of information. I kind of figured that there are at least a couple of people out there that could use it to understand navigating around the local area.
I sent an E-Mail to an engineer friend of mine that owns a surveying company about 2½ years ago asking him to let me me know in layman's language what the actual milage/distance was in the local area for longitude 85°40' to 85°42', or somewhere in that vicinity. His reply is below.
In round numbers the earth is 24000 miles and 360° circumference
360° = 360 x 60 = 21600 minutes
24000 / 21600 = 1.11 miles per an arc of 0° 01'
Due to bulging of the spheroid and convergence of the meridians that can differ up to about 15% in this local area
So from longitude 85°40' to 85°42' is roughly 2 miles
In Fort Walton Area,
0°00'01" of Longitude is about 87 feet
0°00'01" of Latitude is about 102 feet
Consider the normal amount of variation you can get from LORAN readings, then throw in the differences trying to convert LORAN to GPS/DGPS. No wonder I've got this phobia against conversions!
I've had differences in my Garmin III Plus "HOME" setting of up to 57 feet.
This part is from me.. It doesn't take a heck of a lot to mess up some readings, especially considering that those that put up the satellites in the first place,(Our government) has a built in error in case somebody wants to use our system against us.
retafe7
jdereuil
Ensign
36 Posts
Posted - 01/04/2004 : 11:16:31 AM
Hello, and thanks for the work JT, Gulfdiver, et al.
I've got a wad of Loran numbers and just bought the Andren program. Andren (so the program says) can calibrate itself if provided with simultaneous DGPS and Loran readings at a particular location. I really don't want to buy and install a loran, but would like to find these spots the way gulfdiver does.
I've used a couple of the more recent county sites (Mohawk Chief, Sand dollar)to help calibrate the program. I could really use some more, but don't trust the county listings much earlier than 2000(based on reading this site and on plugging some of these older numbers into the program).
I could really use some help if anyone has actual loran and DGPS numbers they've taken simultaneously. Public numbers will do, or even numbers taken simultaneously from your driveway. Will reward for help! Thanks very much.
subdude
Captain
231 Posts
Posted - 01/04/2004 : 12:28:20 PM
I have a handheld Loran. What can I do to help? I can meet you somewhere with your GPS or ???
lemmeknow,
subdude
tjl
Ensign
29 Posts
Posted - 01/04/2004 : 2:44:50 PM
Interesting note that Andren can do a 'calibration'... didn't know that. However, when we first started using the program we did use a loran to double check a # or two, but we weren't using D-GPS yet. I'll check/see if I can find any where I remember confirming both. Worst case we still have access to a hand-held loran, so we can start from scratch. Am outatown first part of Jan, so, it'll take a while for me to get info to you.
Thanks--more later.
tj
quote:
Originally posted by jdereuil
[br]Hello, and thanks for the work JT, Gulfdiver, et al.
I've got a wad of Loran numbers and just bought the Andren program. Andren (so the program says) can calibrate itself if provided with simultaneous DGPS and Loran readings at a particular location. I really don't want to buy and install a loran, but would like to find these spots the way gulfdiver does.
I've used a couple of the more recent county sites (Mohawk Chief, Sand dollar)to help calibrate the program. I could really use some more, but don't trust the county listings much earlier than 2000(based on reading this site and on plugging some of these older numbers into the program).
I could really use some help if anyone has actual loran and DGPS numbers they've taken simultaneously. Public numbers will do, or even numbers taken simultaneously from your driveway. Will reward for help! Thanks very much.
n/a
deleted
6 Posts
Posted - 01/25/2004 : 10:20:21 AM
Just found your great site. I am a long time member and one of the founders of the Volusia County Reef Research Dive Team. I have been using the Andren Program since it was a small DOS program to keep track of the Volusia County artifical reefs for the county and for the team.
I appreciate your posts re conversion from TDs to L/L and calculating ASFs. I have had mixed results here on the east coast of FL in calcualating ASFs. Probably because different LORAN units have been used for the TDs. WAAS GPS has been a big help. Our 13 sites range from 5 to 30 nm offshore. The natural reefs are 20-30 nm offshore.
Checkout our web page at www.volusiareefs.org for info re the team.
Thanks,
John Lane, artreef49@att.net
sea urchin
bayesj
Captain
Eglin Dive Club
463 Posts
Posted - 01/25/2004 : 11:30:47 AM
Lane,
Nice web page with good descriptive info. Looks like you folks have a nice program going. That never happens without a lot of hard work. Please keep us informed as you add to, or update, your reef system.
Bayesj
jdereuil
Ensign
36 Posts
Posted - 04/26/2004 : 11:05:41 AM
Thanks again to JT and contributors to this site. It has helped me tremendously.
I have switched GPS/Sonar units from Garmin to Lowrance.
Garmin uses gps format of DD MM.MMM. Lowrance, unfortunately uses format of DD MM SS.S
It is easy for me to convert by simply multiplying the ".MMM" by 60. My question is, since this often results in a non-round number, how much more error am I introducing to the location by rounding up or down?
Eg) 30 09.726 converts to 30 09' 43.56"
So I round to 30 09 43.6 How many feet off am I now?
Thank you in advance.
P.S. Garmin 188 (monochrome) for sale. Reusing transducer so its not availale. Say $450?
bayesj
Captain
Eglin Dive Club
463 Posts
Posted - 04/26/2004 : 4:54:40 PM
Jdereuil,
At the equator each degree of lat and lon are one nautical mile or 6000'. The lat lines retain equal spacing to either pole. The lon lines slowly converge. In our area, approximately 30.xxx, one degree of lon is only about 4000'. This means .1 is 400', .01 is 40', and .001 is 4'.
Typically bottom machines have about a 6 degree cone pattern. What that translates to is that if you round off to either .5 or .6 (using your example), your bottom finder will show the target you are looking for.
Hope this helps.
Bayesj
Gulf Diver wrote:
The purpose of this posting is to inform all interested in reef coordinates and coordinate conversion as to the many variables that are involved, and one conversion method that works for me.
Reef Coordinates, whether for an artificial or natural reef are typically in one of two formats. The two formats are Loran C and GPS (including DGPS and WAAS). The original position format reference used should be identified. Such as, an artificial reef that was put down with a Loran C reference, or one that is put down with a GPS reference. The original reference for the reef is the most accurate location information for either locating with the same reference equipment or converting to another reference standard. Converted coordinates should be identified as such.
Loran C---position coordinates are given in a set of TD’s (Time Differentials), which are generally called TD1 and TD2. Loran C is a land-based system that uses a set of transmit stations and your loran receiver to approximate your receivers position. This system is subject to variances due to land mass distortions. To compensate for these distortions, most Loran C receivers have an AFS function, which normally is defaulted to be On. Additionally, Loran C receivers can be set up to give position coordinates in latitude and longitude.
GPS---position coordinates are given in latitude and longitude. GPS is a satellite-based system that uses a number of satellites and your GPS receiver to approximate your receiver’s position. This system is not subject to the land mass variances like the Loran C system. It is subject to SA (selective availability), which intentionally transmitted errors to degrade the precision of position finding. SA errors are not currently being transmitted, but can be if the needed to degrade the GPS system. DGPS originated due to SA, and includes the use of additional land based transmitters and a differential beacon receiver interfaced with your GPS receiver. DGPS would remove the bulk of the errors to provide more precision over GPS with SA enabled. WAAS is the newest GPS format that is available and was established initially for aircraft use. It uses correction information that is imbedded in the satellite transmissions. For all practical purposes, without SA errors being transmitted, GPS, DGPS and WASS enabled GPS will all provide a very accurate position in latitude and longitude. Additionally, GPS receivers can be set to give position coordinated in TD’s.
Next, if both Loran C and GPS receivers can provide position coordinates in both TD’s or Latitude and Longitude, then it shouldn’t be a problem to convert from one format to another. Wrong…….. Equipment from different manufactures all produce different results when converting from one format to another. Before looking at how to convert formats, let’s consider a few more of the variables with the actual reported reef locations.
Accuracy of the reported location. Generally, the GPS (including DGPS and WASS) reported locations are very accurate, and can be located regardless of what brand of GPS that you have. Loran C on the other hand, will vary slightly from one brand to another in calibration and the actual TD’s that they produce for the same location. This variance is normally very slight. Was the same Loran C used for all of the reef deployments over the years for your area? Probably not. How did the reported location originate? Did the Tug Captain push save on his Loran C unit when the end loader pushed concrete culvert off of a 200 ft long barge? Did the end loader operator push save on his GPS when he pushed the reef material overboard? Was the tug/barge anchored or drifting during reef material deployment? Did the reported location originate when a boat observed the reef material on its bottom machine? If so, what kind of transducer was used (20, 8, or 6 degree cone)? The most accurate reported location would be with a boat observing the material with a 6 or 8 degree transducer. Also consider the reef size. The larger the target, the easier it should be to locate part of it.
Converting Formats----Most of us are interested in accurately converting from Loran C TD’s to latitude and longitude for use with GPS units. Most reefs deployed prior to 1998 were put down with a Loran C reference. So how do you do the conversion? You find a conversion system that provides the desired accuracy and repeatable accuracy. You can just about be assured that the Loran TD’s for various reefs came from different Loran receivers. You can establish a fixed method of conversion and stick with it. Converting some TD’s to lat/long on your Loran unit, some on your fixed GPS, and some on your handheld GPS will not provide accuracy and repeatability. Also, remember the AFS function of Loran to overcome land mass distortions. The TD’s that you want to convert were probably obtained with AFS enabled. I recommend converting TD’s to Lat/Long with a computer program that also addresses AFS.
1. Select a conversion program that addresses AFS. Select your GPS unit. I use the Loran & GPS Vault program to convert all my TD’s. I use a Megellan 6500 GPS unit with a Magellan DBR-IV differential beacon receiver.
2. Convert from TD’s to Lat/Long. Use your program to convert Loran TD’s to Lat/Long and make sure the AFS function is enabled.
3. Locate and save reef location with your GPS. Use converted coordinate and drop a buoy on the position. Use an expanding circular search to locate the reef and save the actual location. I find that my conversion with the correction factor applied generally holds accurate for the longitude. A north / south search is what I typically need to do to locate the reef.
4. Compare your conversion to the actual GPS Lat/Long. How close is the conversion?
5. Note the difference for a half dozen to dozen of sites. Does the difference remain relatively constant?
6. Average the difference and use it as a correction factor. Throw out the extreme positive and negative differences and average the remaining differences.
7. Add or subtract this correction factor to your conversion for an estimated Lat/Long. I have been using this method and it proves to hold pretty accurate over the entire local area (Offshore Destin), and even works for the Pensacola area with the same correction factor. I subtract 0.030 from both the converted latitude and longitude. I call my conversion with the correction factor the DE (Differential Estimated) location.
The Loran & GPS Vault program is available through:
http://www.worldwidewaypoints.com/
There are many other programs available for your coordinate conversions.
Here is a sample of some of my conversions:
Barrel Barge / DE—N30.21.795, W86.36.097 / DGPS----N30.21.824, W86.36.091
Butler Barge / DE---N30.21.516, W86.35.621 / DGPS----N30.21.523, W86.35.621
AF Barge / DE---N30.21.253, W86.29.578 / DGPS----N30.21.249, W86.29.587
Lost Barge / DE---N30.17.904, W86.27.372 / DGPS----N30.17.894, W86.27.383
Miss Louis / DE---N30.22.294, W86.25.314 / DGPS----N30.22.287, W86.25.317
Good luck on your conversions.
I welcome any comments on conversion methods.
JT
Grand Admiral
1008 Posts
Posted - 03/17/2003 : 7:33:20 PM
This is taken from the Garmin website for those interested in what WAAS is.
You've heard the term WAAS, seen it on packaging and ads for Garmin products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.
The origins of WAAS
The Federal Aviation Administration (FAA) and the Department of Transportation (DOT) are developing the WAAS program for use in precision flight approaches. Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity, and availability. WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing, and satellite orbit errors, and it provides vital integrity information regarding the health of each GPS satellite. Although WAAS has not yet been approved for aviation, the system is available for civilian use such as boaters and recreational GPS users.
How it Works
WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.
Who benefits from WAAS?
Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of WAAS is that it does not require additional receiving equipment, while DGPS does.
Other governments are developing similar satellite-based differential systems. In Asia, it's the Japanese Multi-Functional Satellite Augmentation System (MSAS), while Europe has the Euro Geostationary Navigation Overlay Service (EGNOS). Eventually, GPS users around the world will have access to precise position data using these and other compatible systems.
100 meters: Accuracy of the original GPS system, which was subject to accuracy degradation under the government-imposed Selective Availability (SA) program.
15 meters: Typical GPS position accuracy without SA.
3-5 meters: Typical differential GPS (DGPS) position accuracy.
< 3 meters: Typical WAAS position accuracy.
JT
Grand Admiral
1008 Posts
Posted - 03/20/2003 : 09:38:17 AM
The nomenclature that I am going to use on each reef is:
Coordinates Confirmed -- This means someone has posted good numbers that are different from the posted numbers
+Coordinates VERIFIED+ -- This means someone posted WAAS or DGPS numbers that matched the posted numbers, or two people have posted almost identical numbers.
JT
Grand Admiral
1008 Posts
Posted - 03/20/2003 : 10:15:04 AM
I also want to note that my numbers, as well as other posted on here, may not line up with others because of bottom machine configurations. For starters, no one's transducer is perfectly aimed to show the bottom directly under the boat. I know for a fact that mine is picking up objects slightly in front of my boat at 80 feet deep. You also have to consider that if the boat is not perfectly level and there are waves, then the beam will be varying because of that as well.
So, while the numbers posted may not be *perfect* coordinates, they should be able to get you close enough that you should have no problem finding the reefs.
tjl
Ensign
29 Posts
Posted - 04/05/2003 : 10:27:43 AM
Hmmm... technical difficulties . Just drafted a reply to this and, poof, it's gone. Oh well... here's another try.
First, I really appreciate the time and effort you guys put into this thread--it's great info.
Then, I wonder what you think of this take. I normally use my GPS in the map view. When zooming down to 3 meters the boat pretty much covers the screen. So, when trying to find a site (converted by either the Andren s/w or my Garmin GPS, which seem to use about the same algorythm) I zoom out to 120 feet. That gives better perspective of boat movement/turning in relation to the target. I haven't tried to find any culverts with WAAS yet, but since most of our sites are substantially larger than 3 meters, I find WAAS less meaningful than expected.
Let me know if my 'plain farmer' approach holds water from your view.
Cheers, tj
tjl
Ensign
29 Posts
Posted - 04/05/2003 : 10:33:14 AM
Whoops, my cranial spellchecker says that's 'algorithm'
gulfdiver
Grand Admiral
944 Posts
Posted - 04/08/2003 : 12:28:38 PM
tjl--sounds like you have refined the area search by using your GPS in map view. As far as your conversions from TD's to Lat/Long go, does both your GPS and Adren s/w provide the same conversion? Do you use a correction factor to further refine the converted numbers? Are your conversions with or without a corection factor pretty accurate throughout the entire area? Snake166 informed me that he converts with his GPS and then applies a correction factor for his conversions.
Edited by - gulfdiver on 04/08/2003 12:31:12 PM
tjl
Ensign
29 Posts
Posted - 04/09/2003 : 1:58:13 PM
The GPS and Andren have been identical in the few times I've compared them. I never heard of the conversion factor before reading yr posts.
tj
n/a
deleted
111 Posts
Posted - 07/05/2003 : 09:06:50 AM
There's a lot of, for lack of a better word, error built into any conversion from LORAN to GPS/DGPS. A lot of information can be found at this site
http://pollux.nss.nima.mil/index/index.html
n/a
deleted
111 Posts
Posted - 07/05/2003 : 09:41:25 AM
Theres a lot of info on LORAN and GPS/DGPS at this site.
http://www.floridaconservation.org/marine/lorangpsdgps.htm
n/a
deleted
111 Posts
Posted - 07/08/2003 : 4:49:47 PM
Question time. Two friends of mine (one a diver) that gave up fishing/diving/boating gave their location books to me. I copied them, and gave them back in case they decide to get back into this madness again. Almost all coordinates are LORAN numbers. My question is, should I post them a few at a time, or not. Some seem to be almost to Panama City, and some to Pensacola. And, some are way off shore (at least they seem to be). I'm not an avid fan of converting these numbers to GPS. Here's one that was listed as "Good", 13711.5 47114.9, or one listed as "Rock", 13480.4 46977.0. And, one that was listed as "Junk", but it also said that there were Red Snapper, Triggerfish, Scamp, Flounder, and Grouper there. If these are repeats of previously listed sites, sorry. Now, should I start posting or not?
tjl
Ensign
29 Posts
Posted - 07/08/2003 : 9:02:51 PM
Nice--thanks
tj
quote:
Originally posted by retafe7
[br]Theres a lot of info on LORAN and GPS/DGPS at this site.
http://www.floridaconservation.org/marine/lorangpsdgps.htm
gulfdiver
Grand Admiral
944 Posts
Posted - 07/08/2003 : 10:28:57 PM
retafe7---Please post any td's or lat/long coordinates that you want to post. The more the better. Loran Td's are OK to post. I have very good success in converting these to lat/long coordinates. I used to search for TD's with my loran unit, but have since refined converting the coordinates to lat/long that I now typically convert and locate with my DGPS unit. Your above TD's convert to: Good--(13711.5 & 47114.9) N30.18.345 and W86.29.825; Rock (13480.4 & 46977.0) N29.55.194 and 86.48.515. Please post away.
JT
Grand Admiral
1008 Posts
Posted - 07/09/2003 : 09:01:48 AM
Go ahead and post them, but please do so in the "Non Published Reef" Topic
Thanks,
~JT
n/a
deleted
111 Posts
Posted - 07/26/2003 : 7:57:39 PM
I almost forgot that I had saved this bit of information. I kind of figured that there are at least a couple of people out there that could use it to understand navigating around the local area.
I sent an E-Mail to an engineer friend of mine that owns a surveying company about 2½ years ago asking him to let me me know in layman's language what the actual milage/distance was in the local area for longitude 85°40' to 85°42', or somewhere in that vicinity. His reply is below.
In round numbers the earth is 24000 miles and 360° circumference
360° = 360 x 60 = 21600 minutes
24000 / 21600 = 1.11 miles per an arc of 0° 01'
Due to bulging of the spheroid and convergence of the meridians that can differ up to about 15% in this local area
So from longitude 85°40' to 85°42' is roughly 2 miles
In Fort Walton Area,
0°00'01" of Longitude is about 87 feet
0°00'01" of Latitude is about 102 feet
Consider the normal amount of variation you can get from LORAN readings, then throw in the differences trying to convert LORAN to GPS/DGPS. No wonder I've got this phobia against conversions!
I've had differences in my Garmin III Plus "HOME" setting of up to 57 feet.
This part is from me.. It doesn't take a heck of a lot to mess up some readings, especially considering that those that put up the satellites in the first place,(Our government) has a built in error in case somebody wants to use our system against us.
retafe7
jdereuil
Ensign
36 Posts
Posted - 01/04/2004 : 11:16:31 AM
Hello, and thanks for the work JT, Gulfdiver, et al.
I've got a wad of Loran numbers and just bought the Andren program. Andren (so the program says) can calibrate itself if provided with simultaneous DGPS and Loran readings at a particular location. I really don't want to buy and install a loran, but would like to find these spots the way gulfdiver does.
I've used a couple of the more recent county sites (Mohawk Chief, Sand dollar)to help calibrate the program. I could really use some more, but don't trust the county listings much earlier than 2000(based on reading this site and on plugging some of these older numbers into the program).
I could really use some help if anyone has actual loran and DGPS numbers they've taken simultaneously. Public numbers will do, or even numbers taken simultaneously from your driveway. Will reward for help! Thanks very much.
subdude
Captain
231 Posts
Posted - 01/04/2004 : 12:28:20 PM
I have a handheld Loran. What can I do to help? I can meet you somewhere with your GPS or ???
lemmeknow,
subdude
tjl
Ensign
29 Posts
Posted - 01/04/2004 : 2:44:50 PM
Interesting note that Andren can do a 'calibration'... didn't know that. However, when we first started using the program we did use a loran to double check a # or two, but we weren't using D-GPS yet. I'll check/see if I can find any where I remember confirming both. Worst case we still have access to a hand-held loran, so we can start from scratch. Am outatown first part of Jan, so, it'll take a while for me to get info to you.
Thanks--more later.
tj
quote:
Originally posted by jdereuil
[br]Hello, and thanks for the work JT, Gulfdiver, et al.
I've got a wad of Loran numbers and just bought the Andren program. Andren (so the program says) can calibrate itself if provided with simultaneous DGPS and Loran readings at a particular location. I really don't want to buy and install a loran, but would like to find these spots the way gulfdiver does.
I've used a couple of the more recent county sites (Mohawk Chief, Sand dollar)to help calibrate the program. I could really use some more, but don't trust the county listings much earlier than 2000(based on reading this site and on plugging some of these older numbers into the program).
I could really use some help if anyone has actual loran and DGPS numbers they've taken simultaneously. Public numbers will do, or even numbers taken simultaneously from your driveway. Will reward for help! Thanks very much.
n/a
deleted
6 Posts
Posted - 01/25/2004 : 10:20:21 AM
Just found your great site. I am a long time member and one of the founders of the Volusia County Reef Research Dive Team. I have been using the Andren Program since it was a small DOS program to keep track of the Volusia County artifical reefs for the county and for the team.
I appreciate your posts re conversion from TDs to L/L and calculating ASFs. I have had mixed results here on the east coast of FL in calcualating ASFs. Probably because different LORAN units have been used for the TDs. WAAS GPS has been a big help. Our 13 sites range from 5 to 30 nm offshore. The natural reefs are 20-30 nm offshore.
Checkout our web page at www.volusiareefs.org for info re the team.
Thanks,
John Lane, artreef49@att.net
sea urchin
bayesj
Captain
Eglin Dive Club
463 Posts
Posted - 01/25/2004 : 11:30:47 AM
Lane,
Nice web page with good descriptive info. Looks like you folks have a nice program going. That never happens without a lot of hard work. Please keep us informed as you add to, or update, your reef system.
Bayesj
jdereuil
Ensign
36 Posts
Posted - 04/26/2004 : 11:05:41 AM
Thanks again to JT and contributors to this site. It has helped me tremendously.
I have switched GPS/Sonar units from Garmin to Lowrance.
Garmin uses gps format of DD MM.MMM. Lowrance, unfortunately uses format of DD MM SS.S
It is easy for me to convert by simply multiplying the ".MMM" by 60. My question is, since this often results in a non-round number, how much more error am I introducing to the location by rounding up or down?
Eg) 30 09.726 converts to 30 09' 43.56"
So I round to 30 09 43.6 How many feet off am I now?
Thank you in advance.
P.S. Garmin 188 (monochrome) for sale. Reusing transducer so its not availale. Say $450?
bayesj
Captain
Eglin Dive Club
463 Posts
Posted - 04/26/2004 : 4:54:40 PM
Jdereuil,
At the equator each degree of lat and lon are one nautical mile or 6000'. The lat lines retain equal spacing to either pole. The lon lines slowly converge. In our area, approximately 30.xxx, one degree of lon is only about 4000'. This means .1 is 400', .01 is 40', and .001 is 4'.
Typically bottom machines have about a 6 degree cone pattern. What that translates to is that if you round off to either .5 or .6 (using your example), your bottom finder will show the target you are looking for.
Hope this helps.
Bayesj