[Proj] Azimuthal Equidistant question

[OvV_HN]

In reply to:

[Proj] Azimuthal Equidistant question
Joseph White JWhite at terragotech.com
Fri Sep 28 08:33:59 EST 2012

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.

etc.


Reply:

Your values seem quite normal.
The values for the spherical azimuthal equidistant projection are 
mathematically correct.
Are they really that far off?
The geonames.org server gives for Tucson Arizona the coordinates N 32° 13' 
18'', W 110° 55' 35''
You cannot use the ellipsoidal azimuthal equidistant projection (in PROJ) 
for distances greater than about 800 km from (lat0,lon0) or about 7.5 
degrees.
Most ellipsoidal azeq projections are approximations, developed for areas 
like Micronesia or Guam.


Oscar van Vlijmen