Accepted Solutions
Hi Devin,
I pulled down one of the source .TIF Raster Datasets from the .FTP site and had a few things that I wanted to pass along. While the source and processed output datasets are both .TIFs the compression algorithms used to reduce their size on disk is different. If you load one of the source raster datasets into ArcMap and navigate to the dataset properties, you will notice that the compression utilized is JPEG YCbCr.
This compression algorithm is utilized for 8-Bit 3-Band natural color imagery which is exactly what these Raster Datasets are. This compression is lossy and converts the image to a different spectral domain which improves compression however this cannot be decompressed by numerous GIS applications. Unfortunately, these datasets are not supported in ArcPad. ArcPad is a mobile application and as such does not have access to the full suite of GDAL.dlls as is the case with ArcMap. Also keep in mind that the reason the processed datasets grew by a large factor is that LZW is a lossless compression that under most circumstances can only achieve a compression factor of 2:1. This would explain the exponential file growth on disk. You can use the ArcPad Data Manager to check the source .TIFs out to a background image. My testing revealed that a Single Raster Dataset exported to a JPEG2000 Background Image produced an .APM roughly 500MB in total size. This will obviously limit the ability to work with these datasets in the field on a mobile device.
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Hi Devin,
I pulled down one of the source .TIF Raster Datasets from the .FTP site and had a few things that I wanted to pass along. While the source and processed output datasets are both .TIFs the compression algorithms used to reduce their size on disk is different. If you load one of the source raster datasets into ArcMap and navigate to the dataset properties, you will notice that the compression utilized is JPEG YCbCr.
This compression algorithm is utilized for 8-Bit 3-Band natural color imagery which is exactly what these Raster Datasets are. This compression is lossy and converts the image to a different spectral domain which improves compression however this cannot be decompressed by numerous GIS applications. Unfortunately, these datasets are not supported in ArcPad. ArcPad is a mobile application and as such does not have access to the full suite of GDAL.dlls as is the case with ArcMap. Also keep in mind that the reason the processed datasets grew by a large factor is that LZW is a lossless compression that under most circumstances can only achieve a compression factor of 2:1. This would explain the exponential file growth on disk. You can use the ArcPad Data Manager to check the source .TIFs out to a background image. My testing revealed that a Single Raster Dataset exported to a JPEG2000 Background Image produced an .APM roughly 500MB in total size. This will obviously limit the ability to work with these datasets in the field on a mobile device.
