Situation: Raster (georef. Tifs) that either have no NoData value assigned or a NoData value outside the spectrum (for example, the value 256 for 8-bit). When transforming these grids from one coordinate system to another, white wedges appear on the edge. How can these NoData values be found in the implementation with FME transformers and how can these transformation wedges be eliminated? The position of the NoData values is unknown.
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31 January 2020
Hi @hstepan,
The wedges are formed by the rotation of the image during the transformation. In order to retain all the information in the image, FME expands the extents to include all the rotated image, filling in the null areas with NoData (if set) or the background color.
If the image NoData value is missing or invalid, you can set it using the RasterBandNodataSetter transformer. This works best for numeric rasters.
For imagery, I would recommend using the RasterInterpretationCoercer to add an alpha band to raster. This will cause the wedges to be given an alpha value of 0, making them transparent in most viewers.
If you are mosaicking the rasters after transforming, you can choose whether to use the NoData or alpha band to control transparency when overlaying the rasters.
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