I have 0.5 degree GFS model data defined in a Lat/Long geographic datum (4052).
I want to decimate this to a grid with 1.25 degree spacing and subset to a 90
deg lat / long region. This is being done as a precursor to creating a GFS
'thin-grid'. Hence, the starting and endpoint points are important. They must
be [-90, 0] for lat and -[120,-30] for longitude and the grid spacing must be
1.25 degrees.
Required domain:
[-90,0] lat with 1.25 degree increment
[-120,-30] with 1.25 degree increment
When I make a standard WCS GetCoverage request using the lat/long bounds above,
I receive the following lat/long points.
[-90, 0) lat with 0.5 degree increments
(-119.5, -30] long with 0.5 degree increment
I can easily tweak the requested area to include the 0 lat and -120 long that
are excluded by extending my subset range by 0.5 degrees. This is promising as
the correct start and stop points exist. All I need to do is change the grid
spacing.
When I add a scaleFactor of 0.4 to the previous request, the grid returned is
completely different. Worth noting that 1.25 degree fits nicely into the 90
degree sectors (90/1.25 = 72). Unfortunately, when I add scaleFactor to the
request, I obtain a completely different grid. The grid spacing is 1.25
degrees.
[-89.125, -0.375] lat with 1.25 degree increments
[-119.625, -30.875] long with 1.25 degree increments
Is there any way to obtain my required domain from a GetCoverage request?
Perhaps a way to make a GetCoverage response start with a point from the
original grid?
How is the first point determined when scaleFactors are applied?
The request I made is below. I included scaleFactor elements for clarity.
<wcs:GetCoverage
xmlns:wcs="http://www.opengis.net/wcs/2.0";
xmlns:faawcs="http://faa.gov/wcs/1.0";
xmlns:gml="http://www.opengis.net/gml/3.2";
xmlns:scal="http://www.opengis.net/WCS_service-extension_scaling/1.0";
xmlns:int="http://www.opengis.net/wcs/interpolation/1.0";
xmlns:wcscrs="http://www.opengis.net/wcs/crs/1.0";
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; service="WCS"
version="2.0.1">
<wcs:Extension>
<wcscrs:subsettingCrs>http://www.opengis.net/def/crs/EPSG/0/4052</wcscrs:subsettingCrs>
<wcscrs:outputCrs>http://www.opengis.net/def/crs/EPSG/0/4052</wcscrs:outputCrs<http://www.opengis.net/def/crs/EPSG/0/4052%3c/wcscrs:outputCrs>>
<scal:Scaling>
<scal:ScaleByFactor>
<scal:scaleFactor>.4</scal:scaleFactor>
</scal:ScaleByFactor>
</scal:Scaling>
</wcs:Extension>
<wcs:CoverageId>NWS__GFS_PRES_SFC</wcs:CoverageId>
<wcs:DimensionTrim>
<wcs:Dimension>Lat</wcs:Dimension>
<wcs:TrimLow>-90</wcs:TrimLow>
<wcs:TrimHigh>0</wcs:TrimHigh>
</wcs:DimensionTrim>
<wcs:DimensionTrim>
<wcs:Dimension>Long</wcs:Dimension>
<wcs:TrimLow>-120</wcs:TrimLow>
<wcs:TrimHigh>-30</wcs:TrimHigh>
</wcs:DimensionTrim>
<wcs:format>application/x-netcdf4</wcs:format>
</wcs:GetCoverage>
Jerry
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