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The word 'mosaic' is often used for quite different things within the worlds of ArcGIS and GDAL.

With GDAL and it's downstream applications like Qgis it is common to see mosaic used in the context of "assemble all these tiled images so they appear as one big image", with and gdalmerge put forth as a convenient means of getting there.

ArcGIS has the same starting point, "assemble all these tiled images so they appear as one big image", and then goes on to add "while doing so [blend, min, max, mean, sum, ...] the overlapping pixels" and a few other things.

To put in uncharitably, in this regard ArcGIS is smart and GDAL is stupid.

However it's pretty evident GDAL is not stupid, so my question is: in the GDAL and/or Qgis tool chain what is the equivalent workflow to ArcGIS mosaic?

(note, I'm not talking about the Mosaic Dataset, which is a different beast altogether)

  • Sounds like you may be referring to equivalent applications of ArcGIS's Mosaic to New Raster: resources.arcgis.com/en/help/main/10.2/index.html#//… – Aaron Mar 12 '14 at 20:15
  • Also, are you also looking for control of how overlapping pixels are handled (e.g. blend, max, min etc)? – Aaron Mar 12 '14 at 20:29
  • I don't know about such functionality with gdal. If you look at other OS software, I don't see anything like that with GRASS and it is also not available in the OTB applications. The best seems to be [BEAM][1] which provides the mean value of valid pixels in case of overlap. – radouxju Mar 13 '14 at 6:33
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    @Aaron in this context Mosaic and MosaicToNewRaster are the same thing, and yes I'm looking for control of how overlap is handled. – matt wilkie Mar 13 '14 at 18:27
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I think that the distinction between a full GIS and a raster/vector data access library (admittedly with some extremely useful GIS functionality and utilities) needs to be taken into consideration when comparing ArcGIS and GDAL capabilities. Noting that ArcGIS as of v10 uses GDAL for much of its underlying raster data I/O.

That said, GDAL mosaicing functionality is definitely limited in comparison to ArcGIS with regard to the overlap handling (but then again ArcGIS mosaic/mosaic to new raster is not very clever when compared to ENVI and Imagine which also include seamline/feathering and colour balancing functionality).

So to provide at least a token attempt at answering your question... I don't know of any existing equivalent workflow to mosaic while handling overlaps in a smarter manner in GDAL. But as I said, GDAL is a library, so this functionality could be developed on top of GDAL. A starting point might be the VRT pixel function capability of the "VRTDerivedRasterBand" subclass which can be developed as c/c++ plugins (or even as part of a python script).

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    There was no intent to compare the full system against a library, just a single tool from that system (Mosaic) against a single process/workflow which I think is in the library but just can't find. Thanks for bringing in Envi & Imagine. I have no meaningful exposure to them, so it's good to expand the horizon. – matt wilkie Mar 13 '14 at 18:24

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