I have 37 very large DEM rasters that I am trying to stitch together using the mosaic to new raster tool in Arc. Each raster has a cellsize of 3.125 by 3.125 ft. There are approximately 25,000 rows and 25,000 columns in each raster and they take up about 2 GB. The issue I'm having is that mosaicing the rasters is taking an extremely long time. Several hours or more just to stitch 2 rasters together and the length of time increases as the extent grows from more rasters being added. I understand this may be the norm for such large datasets, however I am using a top-of-the-line machine to perform these tasks and I am wondering if there is a way to speed things up by altering some settings. Here are my questions.
1) If I change the environment settings to "not generate pyramids" or "not generate statistics" does this increase the speed at which two rasters are mosaiced?
2) Of the many mosaicing tools, which one is the fastest? Is it faster to use mosaic to new raster, or to create an empty raster first and then use one of the other mosaicing tools?
3) Ultimately, once all 37 rasters are mosaiced, the extent will be very large. Is it faster to first generate an empty raster with the same extents as the combined 37 rasters, and fill it with <null> values, then mosaic all the rasters to that dataset?
4) Are there any other tools/settings that will increase mosaic speed without any loss of data resolution?
For big raster data it's recommended to use Mosaic dataset. It does not physically merge rasters but enables to conduct analysis like on one raster. Mosaic dataset can be created since version 10.0 (at least ArcEditor/Standard license) in geodatabase with Create Mosaic Dataset tool. Rasters are added with Add Rasters To Mosaic Dataset tool. You can also use right mouse button context menu.
Some thoughts about Mosaic To New Raster. Try different output raster formats. I noticed that in some situations ESRI Grid (no file extension) is created faster and occupies less space than .tif or .img. Calculating pyramids and statistics takes some time but it doesn't slow mosaicing dramatically.