Wednesday, February 24, 2016

Joys and tribulations of the mosaic dataset

Recently I've been really enjoying some of the benefits that the new mosaic dataset file format in ArcGIS has to offer.  For starters I usually work with large imagery collections that are too large to mosaic into a single file.  The ability to seamlessly and virtually mosaic imagery has been refreshing, and I've been satisfied with performance.  I'm also enthralled with Google Earth Engine and other cloud-based processing options, but sometimes it is nice to be able to have the data on-hand and useable within desktop GIS.

For all of the advantages of mosaic datasets there are a handful of disadvantages that are not well advertised by Esri.  We recently have encountered the message "Distributing mosaic dataset operation across four parallel instances on specified host" followed by the dreaded 99999 error.  It didn't take too long to figure out that the large raster tiles (>500 Mb) couldn't be processed on a computer with 8 Gb RAM.  When trying it on a computer with 32 Gb RAM the problem was miraculously resolved.  Lesson learned: if you are going to be building mosaic datasets do it on a computer with lots of RAM or else use many small tiles.

Our other discovery is the need for full path names.  Drive letters are almost never a problem for regular geoprocessing, but when it comes to being able to view the mosaic dataset across different computers with different mapped drive letters it becomes imperative!

No comments:

Post a Comment