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FME fails with a file read or write error when reading a large number of source raster files.
For the best performance,FME's raster processing uses a "pull" model,where the source pixels are read only when required to write a destination pixel.However,this model requires that all of the source images be open at the same time.
The C runtime library used when compiling FME limits the maximum number of open files to 512 on a Windows operating system.Attempting to read more than 512 source raster images may cause FME to fail while attempting to open a file for reading or writing.Even transformers like the RasterCheckpointer that write temporary files may trigger the failure.
To work around the problem,create a set of smaller sub-mosaics using a RasterMosaicker,then use the RasterCheckpointer to cache them to disk.The subsequent full mosaic will use the checkpointed sub-mosaics as its image source,rather than the original data,avoiding the need to open a large number of files.
Example:
In this example,the RasterPropertiesExtractor is used to get the extents of the source images.The first RasterMosaicker has its Group By set to _min_y,so it will create a sub-mosaic for each horizontal line of source images.The RasterCheckPointer writes the sub-mosaics out to a disk cache.The second RasterMosaicker uses the smaller number of cached images to create the full mosaic.
Because the sub-mosaics are cached to disk,only the source files required for a single sub-mosaic will be open at any given time.The Group By for the sub-mosaicker should be set to an attribute value that will keep the number of source images in a sub-mosaic less than the 512 file limit,while also limiting the number of sub-mosaics to less than 512.In this example we used each horizontal line of source images,but your source data may require a different strategy.
Dataset Fanout Negatively Impacts Performance when Writing Raster Tiles
Raster to Raster Translation (Geotiff to JPEG) with Reprojection
Viewing and Inspecting Rasters
Setting NoData and Adding Alpha Bands to Remove Black Borders
Tiling Raster Data with the RasterTiler
Raster Bit Masks: Making Sense of the Numbers
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