Fix unexpected behaviour in the WCS bbox parameter

[alecsandrei]

Hello,

In tutorial 3, the bbox parameter is not correctly set for the WCS GetCoverage request:

# get parameters for grid
bbox2 = Study_area.bounds.values[0].tolist() # get bbox for the Western Mediterranean Sea study area 
crs2 = Study_area.crs.srs # get crs of the Study Area file

#Adding 2 decimal degrees to each side of the bbox

bbox2 = [bbox2[0]-2,bbox2[1]-2,bbox2[2]+2,bbox2[3]+2]
print(bbox2)

[-7.6, 33.07066846, 18.22312212, 46.42720294]

# GetCoverage request
response = wcs.getCoverage(identifier=[dataset],
                           bbox=bbox2,
                           format='image/tiff',
                           crs=crs2,
                           resx=0.00833333,resy=0.00833333,
                           timeout = 120
                           )
print(response.geturl())
with open(f'data/{dataset.replace(":","_")}.tif','wb') as outfile:
    outfile.write(response.read())

https://ows.emodnet-seabedhabitats.eu/geoserver/emodnet_open_maplibrary/wcs?version=2.0.1&request=GetCoverage&service=WCS&CoverageID=emodnet_open_maplibrary__mediseh_cora&crs=EPSG%3A4326&format=image%2Ftiff

A quick look at the response for DescribeCoverage reveals that the dataset is in EPSG 3857 and requires the X and Y axis labels to correctly define the bounding box.

https://ows.emodnet-seabedhabitats.eu/geoserver/emodnet_open_maplibrary/wcs?SERVICE=WCS&REQUEST=DescribeCoverage&VERSION=2.0.1&CoverageID=emodnet_open_maplibrary__mediseh_cora

<gml:Envelope srsName="http://www.opengis.net/def/crs/EPSG/0/3857" axisLabels="X Y" uomLabels="m m" srsDimension="2">

In this PR, I propose the following change for the snippets above:

# get parameters for grid
Study_area_3857 = Study_area.to_crs('EPSG:3857')
bbox2 = Study_area_3857.bounds.values[0].tolist() # get bbox for the Western Mediterranean Sea study area
crs2 = Study_area_3857.crs.srs

# Adding 2 decimal degrees to each side of the bbox

buffer = 111_000 * 2
subsets = [
    ('X', bbox2[0] - buffer, bbox2[2] + buffer),
    ('Y', bbox2[1] - buffer, bbox2[3] + buffer)
]
print(subsets)

[('X', -845389.1484423319, 2027949.6934754928), ('Y', 3951488.8573080758, 5753792.596194154)]

# GetCoverage request

response = wcs.getCoverage(identifier=[dataset],
                           format='image/tiff',
                           subsets=subsets,
                           timeout=120)
print(response.geturl())
with open(f'data/{dataset.replace(":","_")}.tif','wb') as outfile:
    outfile.write(response.read())

https://ows.emodnet-seabedhabitats.eu/geoserver/emodnet_open_maplibrary/wcs?version=2.0.1&request=GetCoverage&service=WCS&CoverageID=emodnet_open_maplibrary__mediseh_cora&format=image%2Ftiff&subset=X%28-845389.1484423319%2C2027949.6934754928%29&subset=Y%283951488.8573080758%2C5753792.596194154%29

Notice that the crs and resolution parameters are no longer required. Also, the printed link includes the bbox values.

This downloads the data using the right bounds.

[tim-collart]

Thanks @alecsandrei for flagging. @M-Mks , can you look into this proposed fix and merge it in?
Cheers,
Tim