DEM-Hydro Processing scripts

DEM visualization

The DEM Visualization script creates a color composite for you a DEM. First, three shadow maps are created by the script, using three different shadow filters. The combination of them in a color composite gives a very good impression of the relief in your area.

Dialog box options:

DEM:	Select a raster map with height values, i.e. your DEM.
Output map:	Type a name for the output color composite raster map that is a combination of three different shadow maps.

Short explanation of the calculations by the script:

First three shadow maps are created using the shadow filters ShadowW (West), Shadow (North-West) and ShadowN (North).
The three shadow maps are stretched using linear stretching, ignoring 5%.
The color composite that is created from these stretched shadow maps is a 24-bit color composite with linear stretching.
Finally, temporary raster maps are removed, and the output color composite of the shadow maps is shown (first picture below).

Tips:

To display the relief of your study area, you can perform the following steps:

Display your DEM and create a new representation for it: use for smaller height values the color green, and use for larger height values the color brown.
For more information, see Display Options : Raster map domain Value.
Add the output color composite shadow map, use a transparency of 70%. For more information, see Display Options : Raster map domain Color.
The result of these two layers is shown in the second picture below.
Finally, add your drainage network (segments from drainage network ordering), using Display by Attribute StrahlerClass.
Then edit the representation for the segments: make all segments blue, assign small Strahler values a thin line width, and assign larger Strahler values a larger line width.
The result is shown in the third picture below.

The drainage network now really stands out very nicely in the relief of your study area.

Results:

Output color composite from the shadow maps:		Transparent color composite with DEM:


Drainage network on transparent color composite and DEM:

Definition of the shadow filters used:

The three shadow filters that are used are defined as follows:

ShadowW (West)

-2	-1	2
-3	1	4
-2	-1	2

Shadow (North-West)

-3	-2	-1
-2	1	2
-1	2	4

ShadowN (North)

-2	-3	-2
-1	1	-1
2	4	2