JCLambert GIS Enterprise: Lab 4 M2.1 Surfaces

This week’s lab delved into TINs (Triangular Irregular Networks) and DEMs(Digital Elevation Models) created, edited, and analyzed each of these. If you search in ESRI’s help, which is very informative, it distinguishes between these two where a TIN is vector-based and preserves the precision of input data while a DEM is a raster-based representation of a continuous surface. Thus, the TIN is more accurate than a DEM. It is visible in the results where triangles are completed by the points that represent the terrain surface, the preservation of data. Dr. Zandbergen in his lecture is also clear on the distinction between the two. “[For a DEM] there is nothing special about its data structure or values. So you have to know that the cell values represent elevation to be sure that it is indeed a DEM. This is different from a TIN, where the data model itself defines a 3D surface.”

In ArcGIS, we worked in Local Scene to better represent the data in 3D. Once again there were several tools used and sequential steps to follow to get the desired output for the deliverables. For the TIN and DEM, the vertical exaggeration was set at 2.00 and contour lines were set at 100m. The TIN is more accurate and what makes the TIN more accurate is the points that can be randomly spaced for the measured elevation points. One of the biggest differences is the contour lines of the DEM appear more widely spaced in some areas and closer in others where the terrain is very steep. Even though it closely resembles the TIN it is apparent that the accuracy is not as complete, even with the interval set at 100 for each. Even with the better accuracy of the TIN the DEM is still close to it as a representation for elevation.

Comparable view of very close proximity to the same location

I have not worked with TINs very much. It is interesting to see the differences between it and a DEM. They are close and both serve a purpose. It is clear that both represent terrain effectively but for better accuracy go with the TIN. The image below shows a TIN where slope, aspect, and edges were added. Once these renderers are set you can click on any triangle to get the value of each.