Lambert projection coordinates conversion?

[sergeolivier]

Hello,

I am planning a trip to Costa Rica next year and I want to explore some caves. I bought the Report of Work 1988 to 1991 - Costa Rica Project, edited by Norma Dee Peacock and John C. Hempel and it contains many good cave maps, but all location is in Lambert projection. First time I heard about that!

So, I trying to convert Lambert projection coordinates in Latitude/Longitude, for use with my GPS. After several research on the net, it seems that there are many Lambert system projections and I don't know what to do with these. I load Convers, a software who make many conversions but it doesn't give the good location coordinates I want.

Hope and Jeff Uhl are the ones who made the caves cartography, but I cannot found them in the Listing of NSS Members.

Could someone help me to reach Jeff or Hope, or explain how I can do these conversions?

Serge

[Bob Thrun]

Jeff and Hope Uhl got divorced and Hope remarried. Hope dropped out of caving though she did show up at last year's OTR. I doubt that either Jeff or Hope is mathematical enough to do the conversion. We were using 1:50000 topos with a 1-km grid overprinted. The conversion consisted of looking at the map. There is more than one Lambert projection. If I had one of the topos, I could tell you what the conversion is. I will look at the report and see if there is enough information for me to determine the conversion. USGS Professional Paper 1395 by John Snyder will give you more map projection information than you want. Why not just use lat-lon? What are trying to convert to?

[Aaron Addison]

Something like CorpsCon may be helpful. It is free and designed to convert between coordinate systems and also different datum data.

http://crunch.tec.army.mil/software/corpscon/corpscon.html

Aaron

[Dan Henry]

Apparently there are 2 zones of a Lambert Conical Projection and a Transverse Mercator for Costa Rica.

The following might help.

http://www.asprs.org/resources/GRIDS/04-2008-costarica.pdf

I did check the version of Corpscon I use, and it did not seem to support these grids.

Maybe try http://www.gpsu.co.uk/

Good Luck.

[Bob Thrun]

The coordinate conversion situation is a mess. I understand the situation for the US, but Costa Rica is more complicated. There is a keystroke by keystroke desctiption of a conversion at http://web.utk.edu/~orvis/CR_GPS.pdf

A simpler way to use the grid coordinates would be to get the topo maps.

[George Dasher]

The coordinate project is just where the points plot on the map.

If you are using Lat-Longs(and know the datum), shouldn't the coordinates plot properly on any map?

Since UTM are based on Lat-Longs deep in their heart, I would think they would also plot properly.

Provided, of course, the caves were located correctly in the first place. Which has been my experience--the person doing the location doesn't do it correctly.

In other words, the projection of the map they used shouldn't matter a hoot for point locations. It will matter for line and area locations.

Unless, of course, I am totally wrong about all of this.

[George Dasher]

Oh!!

Hope's last name is now McAdam.

[George Dasher]

If I am wrong about the coordinate systems and plotting, can someone explain it to me?

[Bob Thrun]

The maps give grid coordinates in the "Lambert Projedtion". USGS Professional Paper 1395 attaches Lambert's name to three slightly different conical projections and one cylindrical projection. The Lambert projection that was used is based on the Ocotepeque datum. This datum is not on my GPS. Berween the Mugnier article and PP 1395, and maybe with some help from the Orvis artcle, there is enough information to write custom conversion software. It would not be a trivial job. To convert to WGS 84 it is necessary to convert the grid coordinates to Ocotepeque lat-lon, then shift the Ocotepeque lat-lon to WGS 84 lat-lon. If UTMs are wanted then the is another conversion. Corpscon goes through these steps.

The grid coordinates were used because the 1 km grid was printed in black on the topo maps. If we could inspect the topo maps, we could do a linear transformation based on the grid coordinates of the lat-lon corners of the topo map. There would still be the problem of converting from the Ocotepeque datum the the WGS 84 datum. Orvis has some information on how to do that conversion.

Global Mapper claims to support Ocotepeque. It is $349. A trial version with some features removed is available. The easiest to use solution would be to get the paper maps. The next best would be to follow Orvis' directions.

My first reaction was like George's, but when I looked closely things were not straightforward.

[lleblanc]

Googling around, I found
http://www.mapealo.com/Costaricageodigi ... _datun.pdf
(in Spanish) that compares various conversion methods for the Ocotepeque datum to WGS84. The best results are obtained with the three parameters supplied by Dörries and Roldan, leading to an average error of 2.81 meters. I understand this is for lat/lon data.

You might try using Auriga's Geodesic Converter for the task. Auriga is freeware, and although it's meant to run on a Palm OS PDA, there's a pre-loaded emulator for Windows available in the Download page of the Auriga website (http://www.speleo.qc.ca/Auriga - see the "Trying Auriga without a Palm" section).

After selecting one of the caves in the Main form, use the Cave/Details menu (tap the title bar) to edit its parameters. Select the User datum and tap the Datum button to edit its parameters. The Ocotepeque datum is based on the Clarke 1866 ellipsoid, and the XYZ WGS84 conversion parameters proposed by Dörries and Roldan are 213.12, 9.36 and -74.95. Close the Cave Details form, drop down the Options menu and use the Geodesic Converter to convert coordinates using this new User datum. You may select Lambert coordinates as input and see if that works (assuming you already have some sample data.) If it does, I could add this datum to the next Auriga version later this month. If you connect a GPS (Bluetooth or serial) to Auriga, you may get the WGS84 coordinates automatically converted to another datum upon reception. I could add a Connect button right into that Geodesic Converter (like the one available in the Survey Shot form) so as to display converted coordinates in real time (at most every 5 seconds) without being tied to a specific cave. Keep me posted of the results if you go that way.

One word about Lambert coordinates. They are used in the US, but only for scientific use, contrary to France and Belgium, where until recently, topo maps used them (they now switched to UTM.) Magellan GPS receivers support them, although I hear that their latest receivers do a worse job than they used to. Garmin considers Lambert to be limited to professional use and thus does not support them in its consumer products, instead they suggest Trimble receivers for Lambert.

Regards,


--
Luc Le Blanc
http://www.speleo.qc.ca/Auriga

[Bob Thrun]

There is still the first step in the conversion to WGS 84. The Lambert grid coordinates need to be converted to lat-lon. PROJ4 has a routine to handle the tangent version of Lambert conformal conic projection. After looking at the PROJ4 documentation, I think I would prefer to write a single-purpose program using the formulas in PP 1395.

One word about Lambert coordinates. They are used in the US, but only for scientific use, contrary to France and Belgium,

Lambert conformal conic projection is used for State Plane coordinates and aeronautical charts. PP 1395 lists 50 State Plane zones that use Lambert and 40 that use (not Universal) Transverse Mercator. The State Plane grid coordinates have less distortion than UTM because they cover smaller areas.

[sergeolivier]

Hello everybody!

Thanks a lot for all these informations. I will studied them and come back later to give you the results. Luc Leblanc will put soon the Costa Rica parameters in Auriga to make the coordinates conversion. I hope it will be more easier to do.

Regards

Serge

[Clem_GrottoCenter]

Hi Serge,

I'm a web designer (and a caver as well! ) and I've participated to build different open and free web sites like http://www.GrottoCenter.org (Caving Wiki-like GIS).
I contact you because I think our new web site should interest you: http://twcc.free.fr/converter-en.php, it's a geodesic converter tool that can compute any kind of coordinates from any kind of spacial reference system.
I've just launched it this week.
Tell me what you think.

If you have any question, feel free to contact me!
Cordially,
Clément Ronzon