Loading & Merging Multiple DEMs

There are several ways to load multiple DEMs:  You can select as many DEMs as you want, up the size limits on a single DEM. The current limits are listed with the Help, Program Limits menu choice.  The memory in your computer might limit your ability to manipulate such a DEM, and you probably cannot display every data point simultaneously. If this is a problem you should Thin or Subset the DEMs before the merge.  You should also consider using multiple scales of DEMs for different scales of analysis.

• File, Open submenu with Open and merge DEMs.  You must use the multifile selection option from Windows as you pick files, all of which must be in the same directory.
• Map library  to load and merge multiple DEMs on the fly.  This will bring up a graphical selection window, showing the available DEMs.  Move to the NW corner of the region you want, hold down and drag to the SE corner. The DEMS will be loaded. With UTM based DEMs you can only select DEMs in a single 6 degree zone.

You can savethe merged DEMs from the File, Save DEM menu choice.

You must obey the following rules:

• All DEMs must be the same basic type, UTM-based or lat/long based.
• All DEMs must have the same data spacing.
• If using UTM based DEMs, all must be in the same UTM zone.
• All feet DEMs will be converted to metric.

Instructions for special cases of merging:

• Arbitrary DEM merge

When merging DEMs, MICRODEM loads all the DEMs into memory, determines the size of the merged grid, creates it, and then adds each DEM to the merge.  If you do not have the memory, you could:

• Merge just the DEMs that will be in the corners of the final merge; they will define the required size.
• Then use the Fill holes option (Edit, DEM Holes, Fill holes from reference DEM, Grid in file) which will minimize the memory required.

Last revised 11/9/2018