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Re: MAP_PROJ_INIT [message #78189 is a reply to message #53364]

Sat, 29 October 2011 10:14

lecacheux.alain
Messages: 325
Registered: January 2008

Senior Member

On 29 oct, 18:48, David Fanning <n...@dfanning.com> wrote:
> alx writes:
>> My problem is actually the following: when applying the
>> map_proj_forward function to real data,- that is to say when computing
>> plane coordinates from given GPS longitudes and latitudes, a very
>> standard operation from GPS data -, I find results wrong by a few
>> hundred meters...
>> For instance:
>> IDL> lon0 = 2.1937863d0 & lat0 = 47.3808737d0
>> IDL> map = map_proj_init(101, ELLIPSOID=24, ZONE=31)
>> IDL> print, map_proj_forward(lon0, lat0)
>> 439142.34 5247587.0
>> Actual easting and northing (as calculated by using other tools) are
>> 439144 and 5247806 instead.
>> I then suspect somme error in map_proj_init, or maybe I am not using
>> it correctly.
>> I was wondering if other people had same experience.
>
> Well, this is *exactly* the problem I was having this
> week, and the "other tool" was ENVI. Maybe we are going
> to have to look into this some more. What "other tools"
> are you using?
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.idlcoyote.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")- Masquer le texte des messages précédents -
>
> - Afficher le texte des messages précédents -

> What "other tools" are you using?
Several online tools, like "http://www.rcn.montana.edu/resources/tools/
coordinates.aspx".
But my reference is the french one: "http://geodesie.ign.fr/index.php?
p=53&page=circe".
All these give same results within 1 meter.
alx.

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[Message index]

		map_proj_init By: marit on Sat, 07 April 2007 15:09
		Re: MAP_PROJ_INIT By: David Fanning on Sat, 29 October 2011 11:41
		Re: MAP_PROJ_INIT By: lecacheux.alain on Sat, 29 October 2011 11:10
		Re: MAP_PROJ_INIT By: lecacheux.alain on Sat, 29 October 2011 10:14
		Re: MAP_PROJ_INIT By: David Fanning on Sat, 29 October 2011 09:48
		Re: MAP_PROJ_INIT By: lecacheux.alain on Sat, 29 October 2011 08:27
		Re: MAP_PROJ_INIT By: David Fanning on Sat, 29 October 2011 07:18

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