Combining DEM and flooding areas for realistic 3D view

superstefan

For a river bed I have historic flooding area information as a shape file (vector overlay). I need to generate a new "DEM of the flood" where all the flooded areas have an absolute (fixed) elevation.
Where can I set the elevation attribute?
How to convert vector overlay to an elevation overlay, which could be merged with standard DEM?
Any other approach?

Thea_bmg

You can set the vector elevation in the vector options for the layer (in the Overlay Control Center).  On the Feature Types/Labels/Elevation Tab, you can set the 'Get Elevations from Attribute Value' option to be your elevation attribute.  

To create a DEM that includes the elevation from your flood polygons, you can use the 'create flattened site plan grid' available by selecting your feature with the Digitizer tool, right clicking on the map, and selecting: Advanced Feature Creation Options > Calculate Flattened Site Plan Grid From Selected Areas.  This will allow you to create an additional terrain layer at the elevation of your flood polygon.  If you then export a DEM with both layers on, it will include your historic flood in your exported DEM.

superstefan

Thanks a lot for this comprehensive guide! :-)