Hello everybody!
I'm trying to read values from a VRT file in Python. When I modify
<Scale> or <Offset> it seem not to make any effect.
I have a simple VRT of a Landsat7 file (below). It has neither scale nor
offset. I launch the given script twice:
1st time to test the value of scale and the value from a band and to
change the value of scale.
2nd time I test value of scale and value from a band. The output shows
that the scale has changed, but the value is the same. I would expect
that the second time the value should be 70.
Does it mean that ReadAsArray() doesn't interpret <Scale> and <Offset>
tags? Ot do I do (expect) something wrong?
Thank you!
Anton
Script:
l7 = gdal.Open('L71211005_00520100824_B10.vrt')
print l7.GetRasterBand(1).GetScale()
print l7.GetRasterBand(1).ReadAsArray()[3000, 3000]
l7.GetRasterBand(1).SetScale(2)
l7.FlushCache()
l7 = None
Output:
> python test.py
1.0
35
> python test.py
2.0
35
VRT-file before test:
<VRTDataset rasterXSize="9211" rasterYSize="9021">
<SRS>PROJCS["WGS 84 / UTM zone 33N",GEOGCS["WGS
84",DATUM["WGS_1984",SPHEROID["WGS
84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",15],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","32633"]]</SRS>
<GeoTransform> 3.6178500000000000e+05, 3.0000000000000000e+01,
0.0000000000000000e+00, 8.6874150000000000e+06,
0.0000000000000000e+00, -3.0000000000000000e+01</GeoTransform>
<Metadata>
<MDI key="AREA_OR_POINT">Point</MDI>
</Metadata>
<VRTRasterBand dataType="Byte" band="1">
<Metadata />
<ColorInterp>Gray</ColorInterp>
<SimpleSource>
<SourceFilename
relativeToVRT="1">L71211005_00520100824_B10.TIF</SourceFilename>
<SourceBand>1</SourceBand>
<SourceProperties RasterXSize="9211" RasterYSize="9021"
DataType="Byte" BlockXSize="9211" BlockYSize="1" />
<SrcRect xOff="0" yOff="0" xSize="9211" ySize="9021" />
<DstRect xOff="0" yOff="0" xSize="9211" ySize="9021" />
</SimpleSource>
</VRTRasterBand>
</VRTDataset>
VRT-file after test:
<VRTDataset rasterXSize="9211" rasterYSize="9021">
<SRS>PROJCS["WGS 84 / UTM zone 33N",GEOGCS["WGS
84",DATUM["WGS_1984",SPHEROID["WGS
84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",15],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","32633"]]</SRS>
<GeoTransform> 3.6178500000000000e+05, 3.0000000000000000e+01,
0.0000000000000000e+00, 8.6874150000000000e+06,
0.0000000000000000e+00, -3.0000000000000000e+01</GeoTransform>
<Metadata>
<MDI key="AREA_OR_POINT">Point</MDI>
</Metadata>
<VRTRasterBand dataType="Byte" band="1">
<Metadata />
<Scale>2</Scale>
<ColorInterp>Gray</ColorInterp>
<SimpleSource>
<SourceFilename
relativeToVRT="1">L71211005_00520100824_B10.TIF</SourceFilename>
<SourceBand>1</SourceBand>
<SourceProperties RasterXSize="9211" RasterYSize="9021"
DataType="Byte" BlockXSize="9211" BlockYSize="1" />
<SrcRect xOff="0" yOff="0" xSize="9211" ySize="9021" />
<DstRect xOff="0" yOff="0" xSize="9211" ySize="9021" />
</SimpleSource>
</VRTRasterBand>
</VRTDataset>
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