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Why does gdalwarp from ortho to longlat truncate the poles? It must be possible, otherwise Antarctica would not be there on the plate-carree

gdalwarp image truncated

Why does gdalwarp from ortho to longlat truncate the poles? Lonlat should display -90 to +90 It is the same as eqc isn't it? They are synonyms for Plate-Carre or am I mistaken? Why is the gap showing up? It must be possible otherwise Antarctica would not be there on the plate-carre. Is there an interpolation argument I am missing?

Re-projecting an orthographic image to a equirectangular projection has some sort of problem. The poles are getting truncated. is there a parameter I am missing? Is there a difference between "eqc" "longlat" "plate-carree" ? Is this a fundamental defect in gdal tools?


gdal_translate 
-of Gtiff 
-a_ullr -1666666 1666666 1666666 -1666666  
-a_srs 
    "+proj=ortho  
    +ellps=WGS84 
    +datum=WGS84 
    +lat_0=85 
    +lon_0=45"  
kat.png 
QQQQ-kat-ortho.tif 



gdalwarp 
-t_srs 
    "+proj=longlat 
    +datum=WGS84 
    +ellps=WGS84 
    +units=m"   
QQQQ-kat-ortho.tif
QQQQ-kat-latlon.tif 

gdal_merge.py  
-o QQQQ-kat-eq-merged.tif     
NE1_50M_SR_W_tenth.tif 
QQQQ-kat-latlon.tif

convert QQQQ-kat-eq-merged.tif QQQQ-kat-eq-merged.png

convert QQQQ-kat-latlon.tif QQQQ-kat-latlon.png
Solution

  • Reprojecting an orthographic (ortho) or perspective (nsper) image to equirectangular (eqc) when the map includes polar latitudes,

    REQUIRES the target extents argument: "-te -180 -90 +180 +90"

    or some other set of -te corners that EXPLICITLY extends all the way up to +/-90 Latitudes, else the default xmax is set to Latitude 85. Perhaps gdal REALLY expects Mercator and snips off poles. ?? This does not appear in the documentation anywhere.

    example:

    gdalwarp -te -180 -90 +180 +90 -t_srs "+proj=eqc +datum=WGS84 +ellps=WGS84 +units=m" source_ORTHO.tif target_EQC.tif