Mosaicking a group of tiles into a single seamless grid

Posted originally by Ben Crosby on the original GLW forum - re-posting it in the OpenTopography forums so it is not lost. -cc
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Hello All!

First off, thanks to all that have developed this portal. It is an efficient and elegant tool and I look forward to its further development and growing catalog of available data.

I started working with the existing tiles that are available for Northern CA and ran into a problem when Mosaicking a group of tiles into a single seamless grid. It appears that the default setting for the "Pixel Type" will force some grids to be treated as integer files, thus destroying the high percision data available from LiDAR and giving the landscape a distinctly contoured look.

Here is the form where you must specify that you are inputting 32_BIT_FLOAT data.

http://geology.isu.edu/~crosbenj/images/work/temp/mosaic_form.jpg

Here is an image showing the result if to Mosaic the tiles using the default 8_BIT_UNSIGNED setting. Note that the contoured tile appears to have no data for a good portion of the region...this is because the elevations as assigned in the individual tiles are well below sea level. Everything that is contoured is above sea level. (why the LiDAR data has such low elevations, I don't know)

http://geology.isu.edu/~crosbenj/images/work/temp/mosaic_incorrect.jpg

Here is an image that was processed using the "32_BIT_FLOAT" workaround. Note that the image looks just fine!

http://geology.isu.edu/~crosbenj/images/work/temp/mosaic_correct.jpg

I hope this will help some overcome the confusion that I experienced!

Looking forward,
Ben Crosby (no known relation to Chris...right cuz?)

http://geology.isu.edu/~crosbenj/index.htm
http://geomorphtools.org/