GdalInfo and Mapserver : Difference between data

Question

I'm trying to create a generic XML response from DescribeCoverage response. For my tests, i used Mapserver 7.0.7
With gdalinfo, i got this :

Driver: GTiff/GeoTIFF
Files: geostationary_ir-120_20170619083000_c7142d3e384e192461debbe8c32751c1___b8aedb3f.
tiff
Size is 2288, 2288
Coordinate System is:
PROJCS["Geostationary_Satellite",
    GEOGCS["GCS_unnamed ellipse",
        DATUM["D_unknown",     
            SPHEROID["Unknown",6378160,298.2539162964669]],
        PRIMEM["Greenwich",0],
        UNIT["Degree",0.017453292519943295]],
    PROJECTION["Geostationary_Satellite"],
    PARAMETER["central_meridian",86.5],  
    PARAMETER["satellite_height",35785993.3373],
    PARAMETER["false_easting",0],  
    PARAMETER["false_northing",0], 
    UNIT["Meter",1]]
Origin = (-5732339.950191651470959,5732339.950191651470959)
Pixel Size = (5010.786669747946689,-5010.786669747946689)
Metadata:  
    AREA_OR_POINT=Area
    TIFFTAG_ARTIST=""
        TIFFTAG_DATETIME=2017:06:19 08:30:00
    TIFFTAG_DOCUMENTNAME="TIFF-MF CMS" 126 155 0
    TIFFTAG_HOSTCOMPUTER=REANIM02
        TIFFTAG_IMAGEDESCRIPTION= 126 155 0
    TIFFTAG_RESOLUTIONUNIT=1 (unitless)  
    TIFFTAG_SOFTWARE=Pnm2TiffMF v1.2
    TIFFTAG_XRESOLUTION=1
    TIFFTAG_YRESOLUTION=1
Image Structure Metadata:
    COMPRESSION=JPEG
    INTERLEAVE=BAND
Corner Coordinates:
ERROR 1: tolerance condition error
Upper Left  (-5732339.950, 5732339.950) 
ERROR 1: tolerance condition error
Lower Left  (-5732339.950,-5732339.950) 
ERROR 1: tolerance condition error
Upper Right ( 5732339.950, 5732339.950) 
ERROR 1: tolerance condition error
Lower Right ( 5732339.950,-5732339.950) 
Center      (   0.0000000,   0.0000000) ( 86d30' 0.00"E,  0d 0' 0.01"N)
Band 1 Block=2288x1 Type=Byte, ColorInterp=Gray

With Mapserver DescribeCoverage response, i got this :

... 
    <gml:origin>  
        <gml:Point gml:id="geostationary_ir-120" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">   
            <gml:pos>5729834.556857 -5729834.556857</gml:pos>   
        </gml:Point>
    </gml:origin>
...

Why there is a difference between these data (Origin Point) ?

Moreover, in XML response, the size of the TIFF is 2287 2287 while in gdalinfo is 2288 2288.

Answer 1

When it comes to the origin, there are two things in the play:

1. If srsName="http://www.opengis.net/def/crs/EPSG/0/4326" then the coordinates in WCS DescribeCoverage are expressed in order Latitude-Longitude.
2. In WCS the origin means the centre of the pixel while GDAL reports the origin as the top-left corner of the top left pixel which leads to half-a-pixel shifts in the coordinate values.

Lets examine the longitude coordinate

 (GDAL Lon_coordinate) + (Lon_pixel_size/2) = WCS Lon_coordinate

-573233995 + (5010.78667/2) = -5729834.557

For latitude the equation is

(GDAL Lat_coordinate) - (Lat_pixel_size/2) = WCS Lat_coordinate

So far everything looks fine. However, you have obviously configured the service somehow whong because WCS is adverticing the coverage to be in EPSG:4326 which is obviously not true (EPSG:4326 is from -90 to +90 degrees N and from -180 to +180 degrees E while in your data the numbers are much higher). Unfortunately I do not know how your Geostationary_Satellite CRS should be configured correctly for MapServer.

I can't guess the reason for the output size of 2287 2287 vs. 2288 2288 in the source data. For my mind that should not happen. I would prepare a test case with source data and complete mapfile and send to question to the mapserver-users mailing list.