[gdal-dev] gdalwarp EPSG:32662 problem

[Even Rouault]

I've just tested the 2 definitions with GDAL trunk and proj 4.8.0 and both 
definitions give identical results :

$ gdaltransform -s_srs EPSG:4326 -t_srs "+proj=eqc +lat_ts=0 +lon_0=0 +x_0=0 
+y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs +wktext"
2 49
222638.981586547 5454655.04887041 0

$ gdaltransform -s_srs EPSG:4326 -t_srs "+proj=eqc +lat_ts=0 +lat_0=0 +lon_0=0 
+x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs +wktext"
2 49
222638.981586547 5454655.04887041 0

But Antti guess seems right. Instead of +ellps=WGS84 (or +datum=WGS84), if you 
play with the a (semi-major axis) and b (semi-minor axis) parameters, you can 
see that only +a has an influence, so latest proj version seems to use a 
spherical version of eqc. Reviewing the history of pj_eqc.c ( 
http://trac.osgeo.org/proj/log/trunk/proj/src/PJ_eqc.c ) I don't see where a 
change of behaviour would have happened, but that might be somewhere else in 
proj codebase.

> Hi,
> 
> Sorry for cross posting. This seems like a proj4 issue but might be gdal
> related.
> 
> I've run into a problem that I think is related to a change in the EPSG
> definition for EPSG:32662
> 
> The symptom is that the image after gdalwarp reprojection is about 20km
> south of where it should be.
> 
> old system is correctly aligned:
> 
> GDAL 1.4.2.0, released 2007/06/27
> proj Rel. 4.5.0, 22 Oct 2006
> 
> # WGS 84 / Plate Carree
> <32662> +proj=eqc +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84
> +datum=WGS84 +units=m +no_defs  <>
> 
> new system is shifted about 20km south:
> 
> GDAL 1.9.2, released 2012/10/08
> proj Rel. 4.8.0, 6 March 2012
> 
> # WGS 84 / Plate Carree (deprecated)
> <32662> +proj=eqc +lat_ts=0 +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84
> +units=m +no_defs  <>
> 
> 
> http://spatialreference.org/ref/epsg/32662/
> This indicates that the definition in proj 4.8.0 is wrong. Would the
> +ellps=WGS84 account for this shift?
> 
> Any thoughts on this?
> 
> Thanks,
>    -Steve
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> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
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