I'm using QGIS 3.2.8 as a client for my WCS (1.0.0) server. I can successfully add and view layers, and they are displayed with the correct values at the right positions.
However, my use case is to compute zonal statistics on my WCS-served layers. And these are clearly wrong as they always show a count of 0 pixels, no matter what layers I choose as input. And indeed, raster layer properties show me that my WCS-served layer supposedly has height and width of 0 pixels:
{'BAND_COUNT': 1,
'CRS_AUTHID': 'EPSG:4326',
'EXTENT': '20.0000000000000000,59.6923076920306883 : '
'26.8515421779061363,61.0277777780547837',
'HAS_NODATA_VALUE': True,
'HEIGHT_IN_PIXELS': 0,
'NODATA_VALUE': nan,
'PIXEL_HEIGHT': 1.0,
'PIXEL_WIDTH': 1.0,
'WIDTH_IN_PIXELS': 0,
'X_MAX': 26.851542177906136,
'X_MIN': 20.0,
'Y_MAX': 61.027777778054784,
'Y_MIN': 59.69230769203069}
That's suspicious. And more so, I cannot even select "Histogram" from the layer properties - I guess that is due to those false width and height values.
For debugging, I am logging the requests by QGIS in my WCS. This is a sample request, made when I computed the raster layer properties:
http://localhost:8081/wcs/kvp?service=WCS&version=1.0.0&request=GetCoverage&SERVICE=WCS&VERSION=1.0.0&REQUEST=GetCoverage&FORMAT=netcdf&COVERAGE=FI_HROC_L4D_1M.CHL_mean&TIME=2020-01-01T00:00:00Z&BBOX=21.13517266280027229,59.69230769203068832,24.73223230620099855,61.02777777805478365&CRS=EPSG:4326&RESPONSE_CRS=EPSG:4326&WIDTH=943&HEIGHT=352
The CDL of the response NetCDF is
netcdf kvp10 {
dimensions:
time = 1 ;
lat = 352 ;
lon = 943 ;
variables:
int64 time(time) ;
time:long_name = "time" ;
time:standard_name = "time" ;
time:units = "days since 2020-01-01 00:00:00" ;
time:calendar = "proleptic_gregorian" ;
double lat(lat) ;
lat:_FillValue = NaN ;
lat:long_name = "y coordinate of projection" ;
lat:standard_name = "projection_y_coordinate" ;
double lon(lon) ;
lon:_FillValue = NaN ;
lon:long_name = "x coordinate of projection" ;
lon:standard_name = "projection_x_coordinate" ;
float CHL_mean(time, lat, lon) ;
CHL_mean:_FillValue = NaNf ;
CHL_mean:long_name = "Chlorophyll-a concentration" ;
CHL_mean:standard_name = "mass_concentration_of_chlorophyll_a_in_sea_water" ;
CHL_mean:units = "mg m-3" ;
CHL_mean:valid_min = 0. ;
CHL_mean:grid_mapping = "crs" ;
int64 crs ;
crs:crs_wkt = "GEOGCRS[\"WGS 84\",ENSEMBLE[\"World Geodetic System 1984 ensemble\",MEMBER[\"World Geodetic System 1984 (Transit)\"],MEMBER[\"World Geodetic System 1984 (G730)\"],MEMBER[\"World Geodetic System 1984 (G873)\"],MEMBER[\"World Geodetic System 1984 (G1150)\"],MEMBER[\"World Geodetic System 1984 (G1674)\"],MEMBER[\"World Geodetic System 1984 (G1762)\"],MEMBER[\"World Geodetic System 1984 (G2139)\"],ELLIPSOID[\"WGS 84\",6378137,298.257223563,LENGTHUNIT[\"metre\",1]],ENSEMBLEACCURACY[2.0]],PRIMEM[\"Greenwich\",0,ANGLEUNIT[\"degree\",0.0174532925199433]],CS[ellipsoidal,2],AXIS[\"geodetic latitude (Lat)\",north,ORDER[1],ANGLEUNIT[\"degree\",0.0174532925199433]],AXIS[\"geodetic longitude (Lon)\",east,ORDER[2],ANGLEUNIT[\"degree\",0.0174532925199433]],USAGE[SCOPE[\"Horizontal component of 3D system.\"],AREA[\"World.\"],BBOX[-90,-180,90,180]],ID[\"EPSG\",4326]]" ;
crs:semi_major_axis = 6378137. ;
crs:semi_minor_axis = 6356752.31424518 ;
crs:inverse_flattening = 298.257223563 ;
crs:reference_ellipsoid_name = "WGS 84" ;
crs:longitude_of_prime_meridian = 0. ;
crs:prime_meridian_name = "Greenwich" ;
crs:geographic_crs_name = "WGS 84" ;
crs:grid_mapping_name = "latitude_longitude" ;
data:
time = 0 ;
lat = 61.0258753990149, 61.0220814807016, 61.0182875623884,
61.0144936440752, 61.0106997257619, 61.0069058074487, 61.0031118891355, [...]
lon = 21.1370819301269, 21.1408964111341, 21.1447108921412,
21.1485253731484, 21.1523398541556, 21.1561543351627, 21.1599688161699, [...]
CHL_mean =
5.315124, 5.233703, 5.257952, 5.2307, 4.849386, 4.86493, 5.227843,
5.232719, 4.819328, 5.192392, 5.173487, 5.082797, 5.130269, 5.094828, [...]
crs = 0 ;
}
It looks fine to me, but still I suspect there is something wrong with my WCS response, I only cannot figure out what exactly. The WCS 1.0.0 specification does not exactly specify the response, so I guess I have to know what QGIS expects to make my WCS work with QGIS.
