Projection and Mosaic Datasets

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01-17-2014 11:26 AM
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Say I have an entire state worth of 10m DEM quadrangles.  They come in a GCS NAD 1983.  I was initially under the assumption that I should create the mosaic dataset first of the entire state in the GCS and then reproject to a projected coordinate system.   However, how would I got about doing that?  If I use the project raster tool on the mosaic dataset, it will just become a raster dataset and no longer a mosaic dataset.  Now obviously, I could probably work with that, but it is no longer tied to the source raster files.

Or should I do a batch project raster of each quadrangle before mosaicing? I read somewhere that this would cause issues.  It certainly makes sense that it would when it comes time to put them together.

The end goal is to be able to conduct surface analysis like a hillshade (with illumination and shadows) on the entire state or split portions of the state in pieces if there are processing power or memory limitations. 

Looking to get my mind clear on this.  Thanks in advance.
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Hi BahamutZ,

You can set a projection for the mosaic dataset that is best suited in reducing distortions for your area of interest.  Mosaic datasets are capable of using transformations and re-projecting the added rasters on the fly.   ArcGIS will pick a transformation for you by default, but you can add/edit transformations in the mosaic dataset properties.  The mosaic dataset will read the inital projection of the input raster and then apply the appropriate transformation to reproject.   Below is a blog that might interest you on this subject.

How does a mosaic dataset handle source data with different geographic transformations?
http://blogs.esri.com/esri/arcgis/2013/01/23/how-does-a-mosaic-data-handle-with-various-transformati...

Best Wishes,
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Okay so one would create the mosaic dataset with a projection more suited to a state/study area rather then the original sourced raster data in GCS NAD 1983 or WGS1984?  Then once you add rasters to the mosaic datasets, ArcMap should choose the correct one and project it automatically.  If not, check the tranformation section under Catalog properties to make sure the right transformations exist for the mosaic dataset.

Is that right?
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[ATTACH=CONFIG]30718[/ATTACH]

My hillshade with modeling shadows does not appear to turning out right with the Spatial Analyst Hillshade tool.  I get a display like the attached image when running it on my mosaic dataset.  I am going to assume I cannot do this since this tool wont be able to handle the projecting on the fly that is occuring in the mosaic dataset?

I do get a normal output if I use the mosaic dataset hillshade function (under mosaic dataset-properties-functions), but I can't seem to model shadows using this.  Even if I could,which it doesn't seem like I can,  I will need to pull out the cell values after the hillshade is run. If I merely export the output I just end up getting a checkerboard like image again. 

Can someone potentially walk me though this?  Been trying some other things, but havent had any luck. Thank you.
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