The Art of DEM

The Art of DEM

For some reason, I am drawn to Digital Elevation Models (DEM). They express so much information in such an elegant way.

Their creation does require embedding GPS data, but thats almost a given these days as its a straightforward exercise pulling points out of sonar. In simple terms, a DEM is a 2D image representing a surface model with colours applied to represent common heigh (or in our case, depth) values. As ever, north is at the top of the image.

Once created Aigsoft Photoscan Pro has two ways of presenting a DEM, one in a basic view and again in hillshading mode. Here’s an example of the mystery pontoon as found by Grahame Knott in Weymouth Bay, England:

Two DEM views of the mystery pontoon. On the left, the standard view and on the right is the view with hillshading selected.

Hillshading Explained

Hillshading adds a simulated light source to the scene. Or in other words, adds shadows and relief that helps the human eye interpret the contours. This technique been used in traditional maps for centuries and is part of the art of map making. Its a great way to pick out and visualise smaller details like the tiny scour in the lower left corner of the pontoon. As we have geo reference data and the mode is scaled, we have a scale bar too.

Summary

There is something quite arty about DEMs, particularly in hillshade view. Coupled with the embedded and accurate data they contain they convey a lot of information in a clear way. Its for these reasons – art plus data – means they are one of the first things generated after the model is built. You can add contour lines to them as well, but that’s for another post. In the meantime, here’s another example, the F-2 and YC-21 barge from Scapa Flow:

DEM of the F2 and YC-21 Barge. On the left, the basic DEM and on the right the same view with Hillshading selected.