[Proj] Azimuthal Equidistant question

[Joseph White]

Hi,
Thanks for the replies.  We did find that moving the lat_0, lon_0
parameters into the actual working area solved most of our issues.  This
just appears to be one of those issues where ESRI's projection engine
gives a "better" result than Proj.4 does.  I find myself wondering if
under the hood they move the origin latitude and central meridian into
the work area, then add the difference in origins back as a false
easting / false northing so that the user is unaware of the change.....

In any case, thanks much Janne

Joe White

-----Original Message-----
From: proj-bounces at lists.maptools.org
[mailto:proj-bounces at lists.maptools.org] On Behalf Of
support.mn at elisanet.fi
Sent: Monday, October 01, 2012 8:01 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Azimuthal Equidistant question

Hello,

without going any deep in your question ..

if you are far away from what is expected you might need some additional
parameters to the projection setup... either lat_0, lon_0 needs some
initialization value or x_0 or y_0 is missing something.. or some other
parameter with that projection .. if that does not help then the
projection might be wrong... etc. etc..

regards: Janne.

-------------------------------------------------------------

Joseph White [JWhite at terragotech.com] kirjoitti: 
> Hi, all,
> 
> I'm trying to track down an issue I'm seeing with Azimuthal 
> Equidistant values when compared to ESRI.  The ESRI coordinate system 
> I'm using is World Azimuthal Equidistant.  I'm using some sample data 
> that is in the Tucson AZ area.
> 
>  
> 
> The coordinate strings we're passing into PROJ to set up the transform
> are:
> 
> Src: +proj=aeqd +lat_0=0 +lon_0=0  +x_0=0 +y_0=0 +datum=WGS84 +units=m
> +no_defs
> 
> Dest: +proj=longlat +datum=WGS84 +no_defs
> 
>  
> 
> I pass in the following coordinates (Easting,Northing):
> 
> 1.        -9939304, 6673447
> 
> 2.       -9930938, 6684888
> 
>  
> 
> I get this result:
> 
> 1.        -69d 0' 0.12", 32d 15' 14.159"
> 
> 2.       -68d 59' 24.215", 32d 19' 5.934"
> 
> Needless to say, this isn't anywhere near Tucson, and is about 31-32 
> degrees off longitudinally.
> 
>  
> 
> When I try using a sphere (I've tried both semi major axis and 
> equal-area), the values are much closer, but still off.
> 
> Src: +proj=aeqd +lat_0=0 +lon_0=0  +x_0=0 +y_0=0 +a=6378137.0
> +b=6378137.0 +units=m +no_defs
> 
> Dest: +proj=longlat +a=6378137.0 +b=6378137.0 +no_defs
> 
>  
> 
> 1.        -110d 50' 50.416", 32d 6' 24.361"
> 
> 2.       -110d 51' 24.032", 32d 10' 15.985"
> 
>  
> 
> Src: +proj=aeqd +lat_0=0 +lon_0=0  +x_0=0 +y_0=0 +a=6371007.1809
> +b=6371007.1809 +units=m +no_defs
> 
> Dest: +proj=longlat +a=6371007.1809 +b=6371007.1809 +no_defs
> 
>  
> 
> 1.        -110d 59' 11.622", 32d 4' 58.135"
> 
> 2.       -110d 59' 45.523", 32d' 8' 49.575"
> 
>  
> 
> Does anyone out there have any idea why this is happening?  I'm at my 
> wits end to explain it.
> 
>  
> 
> Thanks
> 
>  
> 
> Joe White
> 
>  
> 
>  
> 
> 
> _______________________________________________
> Proj mailing list
> Proj at lists.maptools.org
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