IMAGIS Education

IMAGIS Classic

Besides interpolation methods, the Triangular Irregular Network (TIN) is the most widely used method for creating DEM's from contour lines and spot heights. Unfortunately, if we use the TIN method in it's simplest form, the resulting DEM is often completely distorted (see Figures 1, 2 and 3):  

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Fig. 1	Original data from Digitized contour lines and spot heights
Fig. 2	TIN generated directly from contours. A number of "flat triangles" result. These are displayed here in yellow.
Fig. 3	Critical deformation of the DEM results. A comparison of the original contours and those generated from the deformed DEM bear little resemblance.

The DEMix Solution:

The main mathematical algorithms in DEMix allow that: 

• "Workflow line points" describing the terrain are generated from the input contour lines
• Heights are assigned to the "structure line points" by means of the input contour lines and spot heights (fig. 4)
• A TIN is generated from the input contour lines and spot heights, with due regard being given to the newly acquired "structure line points" (fig. 5)
• A DEM is interpolated from the TIN and "new" contour lines are generated from the DEM (fig. 6). Fig. 7 shows the superimposition of the input contour lines (black) and the new DEMix derived contour lines (red). At this point it is possible to uncover errors in the original data.
• All of these steps are iterative and can produce converging results

Fig. 4	"Workflow Line Points" are automatically generated from the input contours and spot heights.
Fig. 5	A TIN is generated from the input contours and spot heights with due reference being given to the newly derived "Workflow Line Points". No flat triangles are created.
Fig. 6	The DEM generated from DEMix with the new contours generated from that DEM.
Fig. 7	On-screen comparison of the original contours and those generated from the DEMix derived DEM.

DEMix also produces excellent results in mountainous areas (fig. 8 to fig. 10). 

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Fig. 8	Contours derived solely from TIN with no "Workflow Line Points".
Fig. 9	"Workflow Line Points" derived from DEMix.
Fig. 10	Superimposition of contours derived from DEMix (using "Workflow Line Points") and original contours.