I'm working a set of 30meter DEMs (~40 DEMs) for New England. I've seen a lot of debate on whether to work with (A) the individual DEMs first, and then mosaic the final raster calculations together, or (B) mosaic the original DEMs and then run all other processing on the new mosaic. I'm trying to determine what the best approach is for my specific project.
My eventual goals are as follows:
- Calculate slope for all of New England
- Calculate hillshade for all of New England
- Calculate aspect for all of New England
- Compare slope, hillshade, and aspect with 3 other regional layers (not derived from DEMs)
Would it be best to calculate slope, hillshade, and aspect for each DEM and have separate rasters that then can be mosaicked?
Or mosaic first and calculate on one giant DEM mosaic?
Because the spatial reference of the original DEMs is in UTM, I'm also running into some projection issues (mostly resolved in previous question: mosaic dem with multiple coordinate systems). My data spreads across 2 zones; UTM 19N and UTM 18N.
I have a VERY basic understanding of GIS (using ArcGIS 10.2).
I've mosaicked first and run into some issues with changed values between the original DEM and mosaicked DEM. I just did a small mosaic (2 30m DEM tiles) to see what's happening with the Python code. The code is pasted below:
arcpy.MosaicToNewRaster_management(input_rasters="'F:/MyBook Backup/All Data Files/GIS Data/Geodatabases/Unprojected2.mdb/Pned30m41073';'F:/MyBook Backup/All Data Files/GIS Data/Geodatabases/Unprojected2.mdb/Pned30m41074'",output_location="F:/MyBook Backup/All Data Files/GIS Data/Geodatabases/Unprojected2.mdb",raster_dataset_name_with_extension="Pned41073n074",coordinate_system_for_the_raster="PROJCS['USA_Contiguous_Albers_Equal_Area_Conic_USGS_version',GEOGCS['GCS_North_American_1983',DATUM['D_North_American_1983',SPHEROID['GRS_1980',6378137.0,298.257222101]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]],PROJECTION['Albers'],PARAMETER['False_Easting',0.0],PARAMETER['False_Northing',0.0],PARAMETER['central_meridian',-96.0],PARAMETER['Standard_Parallel_1',29.5],PARAMETER['Standard_Parallel_2',45.5],PARAMETER['latitude_of_origin',23.0],UNIT['Meter',1.0]]",pixel_type="32_BIT_FLOAT",cellsize="#",number_of_bands="1",mosaic_method="BLEND",mosaic_colormap_mode="MATCH")