MATLAB: Mismatch between AREAINT and AREAQUAD around (0,0).

areaintareaquadmappingMapping Toolbox

Dear all,
 E_earth = referenceEllipsoid( 'earth' ) ;
 lat = [-1, 1] + 0 ;  % +0 is placeholder for easy manual shift.
 lon = [-1, 1] + 0 ;
 areaquad( min(lat), min(lon), max(lat), max(lon), E_earth )
 areaint( [min(lat), min(lat), max(lat), max(lat), min(lat), NaN], ...
     [max(lon), min(lon), min(lon), max(lon), max(lon), NaN], E_earth )
This outputs:
 ans =
   4.9234e+10
 ans =
   7.7333e+10
Their ratio is close to pi/2, and the output of AREAQUAD matches what I get with ArcGIS for example.
Thanks!
Cedric

Best Answer

The doc for areaint hints that the accuracy of the function improves with denser sampling. In your you example, you only have the corner points of the quadrangle in the polygon passed to areaint. The function outlinegeoquad can be used to get a more densely sampled boundary of the quadrangle. Using this function, I get answers which are increasing close to that returned by areaquad.
>> E_earth = referenceEllipsoid( 'earth' ) ;
>> [latq,lonq] = outlinegeoquad(lat,lon,0.1,0.1);
>> areaint( latq, lonq, E_earth )
ans =
     4.9304e+10
>> [latq,lonq] = outlinegeoquad(lat,lon,0.01,0.01);
>> areaint( latq, lonq, E_earth )
ans =
     4.9235e+10
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