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how to handle 500+ Hansen/Global Forest Change raster tiles

Question asked by pkundu on Dec 15, 2015
Latest reply on Dec 17, 2015 by pkundu

Hello,

 

I am trying to mosaic the 500+ raster tiles of the Hansen/UMD 2015 GFC forest loss dataset (30m x 30m cell size) into one global dataset and am trying to figure out the most efficient and least time-consuming process to do this. The end result does not necessarily need to be one raster (i.e., using Mosaic to New Raster tool) and I am open to utilizing Mosaic datasets, as long as I can utilize the final product/composite file in Raster Calculator. I do not have much experience using Mosaic datasets prior to this task.

 

So far I have tried the following methods, but each one seems to be very time consuming (several hours to days) and have resulted in numerous crashes:

- Input all the raster tiles into a Mosaic dataset -- this method seems to be taking several hours just to input all the rasters into the mosaic dataset. The first time I ran this, it took about 10 minutes to input all the rasters, but they were not rendering properly. The second time I attempted this, the script is indicating that there are some 11,000 files being generated for the mosaic dataset and it will take several hours to accomplish.

 

- Isolate only the tiles that actually have deforestation values (eliminate tiles over the ocean to reduce # of tiles that need to be processed overall) and then mosaic them -- for this, I thought the best way would be to build raster attribute tables for each, and use the Unique Values symbology to delete rasters with only Value = 0 (No Data), then mosaic the remaining files. I am building the attribute tables for each raster though a simple model in Model Builder, but still, the process is very time-intensive. In addition, I'm not sure how to automate changing the symbology from Stretched (default when you add data to the TOC) to Unique Values and have been doing it manually. In this case, I don't think that batching an Apply Symbology approach would work, because I want to isolate those rasters that have only No Data values to delete them. (Batching the Apply Symbology would make each raster seem like it has values of 0 and 1 (or only 0 values, depending on which raster is used), which would result in more work for me to fix it.)

 

I have also tried just a straight Mosaic to New Raster with all 500 rasters, but it did not complete even after 3 days of processing. I was also considering deleting according to file size, however, there are instances in which the smaller sized files have values of 1/contain deforestation data, so I can't use that kind of blanket approach.

 

Does anyone have any suggestions on how to handle large numbers of rasters in one go? Or, does anyone know of a script to eliminate the GFC tiles that are over ocean only / eliminate the tiles that contain no data?

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