[gdal-dev] Solved: Re: Having a problem getting VRT ComplexSource to Scale

[Stephen Woodbridge]

Never mind! I just checked the histogram and the data is getting scaled, 
I forgot that I was also scaling it in my mapfile so the results  where 
getting masked.

-Steve

On 1/23/2020 8:20 PM, Stephen Woodbridge wrote:
> Hi all,
>
> I'm having trouble getting my VRT file to scale the source data into 
> my ColorTable.
> I've been looking at this https://gdal.org/drivers/raster/vrt.html
>
> The source GeoTiff has:
>
> Band 1 Block=4500x1 Type=Float32, ColorInterp=Gray
>   Minimum=1.082, Maximum=46.322, Mean=34.181, StdDev=2.049
>   NoData Value=-30000
>   Overviews: 2250x2126, 1125x1063, 563x532, 282x266, 141x133, 71x67
>   Metadata:
>     STATISTICS_MAXIMUM=46.321998596191
>     STATISTICS_MEAN=34.181107349018
>     STATISTICS_MINIMUM=1.0819988250732
>     STATISTICS_STDDEV=2.0492649377546
>
> My goal is to scale the source 0-50 into 10-240 in the ColorTable.
>
>
> The VRT looks like:
>
> <VRTDataset rasterXSize="4500" rasterYSize="4251">
>   <GeoTransform> -180.0 ,0.08 , 0 , 90.0 , 0 , -0.04 </GeoTransform>
>   <Metadata>
>   </Metadata>
>   <VRTRasterBand dataType="Byte" band="1">
>     <ColorInterp>Palette</ColorInterp>
>     <ColorTable>
>       <Entry c1="0" c2="0" c3="0" c4="255"/>
>       <Entry c1="0" c2="0" c3="255" c4="255"/>
> ...
>       <Entry c1="255" c2="255" c3="255" c4="255"/>
>     </ColorTable>
>     <ComplexSource>
>       <SourceFilename 
> relativeToVRT="1">HYCOM_tomorrow_salinity_0.tif</SourceFilename>
>       <SourceBand>1</SourceBand>
>       <ScaleOffset>0</ScaleOffset>
>       <ScaleRatio>1</ScaleRatio>
>       <NODATA>0</NODATA>
>       <SrcRect xOff="0" yOff="0" xSize="4500" ySize="4251"/>
>       <DstRect xOff="0" yOff="0" xSize="4500" ySize="4251"/>
>     </ComplexSource>
>   </VRTRasterBand>
> </VRTDataset>
>
> 50 - 0 = 50
> 240 - 10 = 230
> 230 / 50 = 4.6 = ScaleRatio
> 10 = ScaleRatio
>
> I've tried a lot of other value trying to play with the scaling.
>
> I also tried using:
>
> <Exponent>0</Exponent>
>
> <SrcMin>0</SrcMin>
> <SrcMax>50</SrcMax>
> <DstMin>10</DstMin>
> <DstMax>240</DstMax> but that doesn't appear to work either. Using: 
> GDAL 2.2.3, released 2017/11/20 on Unbuntu 18.04 My conclusion is that 
> I'm not understanding the meaning of these fields or these are meant 
> for something other than my goal. Any help would be appreciated. 
> Thanks, -Steve
>