2010-05-28 Updated article to inlcude link to a tutorial.
In MicroStation V8 2004 Edition (08.05.xx), Bentley Descartes was required to drape rasters on a 3D surface using the visualization engine of MicroStation.
In MicroStation V8 XM Edition (08.09.xx), Bentley Descartes was required in order to turn on the Draping toggle in the Raster Manager for the image that was to be draped onto a 3D surface. Once enabled, Descartes was no longer needed; you could simply load dcdrape.pal as a material in the Materials Editor and subsequently drape the image onto a 3D surface.
In MicroStation V8i, (08.07.xx) Descartes is no longer needed to toggle the Draping option in the Raster Manager. As a result the entire draping workflow can be performed in MicroStation and without the need for Descartes.
Attach the raster and ensure the Draping toggle is set on in the Raster Manager. Also note that that the mesh or DTM on which it will be draped overlaps the image when placed in Top view.
Select Settings > Rendering > Materials and load dcdrape.pal as the active palette.
Assign the dcdrape material to the DEM or mesh vectors on which the raster will be draped. This will make the level and color of the selected DEM or mesh display next to the dcdrape material in the Material Editor list. In the example below, dcdrape has been assigned to Level 10 and Colour 1.
If necessary, rotate the view to isometric, and perform the drape using the Visualization > Render tool. Alternatively, set the View Display Style to Smooth.
The following tutorial may also be of interest. It includes a sample dataset and also discusses how to create a DTM from points.
Make a DTM and drape an image MicroStation V8i