Comments and answers for "Merge multiple PNG from the same area with transparency into a PDF"

Comment by david_r on david_r's comment

david_r — Wed, 03 Jan 2018 14:32:21 GMT

Yes, I forgot to mention that possibility.An option is to use the RasterBandMinMaxExtractor and a RasterBandPropertyExtractor and check for

_band{}.min == _band{}.max == _band{}.band_nodata

For bands where that's the case, you can assume the band is completely empty and treat it accordingly.

Unfortunately this can be a bit slow if you have lots of rasters and/or bands, so you should probably weigh this up against your current solution.

Answer by lizsanderson

lizsanderson — Fri, 22 Dec 2017 18:59:26 GMT

Hi@JeroenR, this article works with GeoTIFFs but can also be done with PNG files and written out to PDF.It goes over how to manipulate and merge/overlay different files in FME working with transparency.https://knowledge.safe.com/articles/58374/how-to-convert-geotiff-to-ecw.html Hopefully that helps you get started.

Comment by jeroen on jeroen's answer

jeroen — Fri, 22 Dec 2017 13:21:47 GMT

Thanks, tried this but always got my stuff rejected so i thought it was a non-valid option.Tried it again with the RasterMosaicker, at your suggestion, and found out that if the PNG is completely empty (all values NoData) it fails and gets rejected.(problably no palette to merge).With a logger connected to the rejected port it works like it should.If the bounding box is changed and that certain layer has information everything works fine and nothing gets rejected.

Answer by david_r

david_r — Mon, 18 Dec 2017 10:15:40 GMT

Maybe consider merging all the tiles first using either the RasterMosaicker or perhaps the MapnikRasterizer before sending the result to the PDF writer.