GIS5935 Lab 4

 Surfaces - TINs and DEMs

This week we examined TINs (triangulated irregular networks) and DEMs (digital elevation models). There are pros and cons associated with each of them and neither is exclusively superior to the other. There are many factors to consider when choosing which one to use for your project. For this lab we created 3D visualizations of elevation models, created and modified a TIN, and compared the TIN and DEM contour lines for our study area.

We began by adding an elevation source to give the TIN a 3D surface and using Vertical Exaggeration to visually enhance the depth.

Next, we utilized a DEM to crate a suitability map for a Ski Run. We used various tools such as Rast to TIN, Reclassify, Slop and Aspect. Once we had our various new layers I chose to use Weighted Overlay to create my final suitability raster using the following weights: 25% aspect, 40% elevation and 35% slope. Below is the 3D representation of my results:

Our next step was to add the Bear Lake TIN and examine the data. TINs vector data models made up of irregular triangles. The three points (nodes) of the triangle are made up of elevations data. The node area connected by line segments which become the edges of the TIN. We examined the data, changed the slope, aspect and drew the edges using Simple symbology the results are pictured below:

Lastly, we created a TIN, utilized the Spline tool, created Contours and examined the differences in the TIN contour lines and the DEM contour lines.

TIN contour lines                                                    DEM contour lines

  

Both sets of contour lines are pictured together here in a two different perspectives:

This view is an overhead "bird's eye" view. As you can see here (above) the greatest difference in the two sets appears to be in the lower elevation areas. The sharp lines of the TIN clearly deviate from the curving lines of the DEM.

This view is a closer straight on view of a higher elevation area:

As you can see there appears to be less variation between the TIN and DEM contour lines in this view.

DEMs are more readily available for general use. TINs are data heavy and can be expensive to obtain and process. TINs are more accurate in areas with a greater number of elevation points available and can be more accurate than DEMs. As a result, it is not possible to say than one is better than the other. It is a case by case decision that has to be made weighting all the factors for each project.