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Index of this site:
Hint: For more information about Digital Terrain Models take a look at "definitions of DTM" (e.g. describing the the difference between "Digital Terrain Models" (DTM) and "Digital Elevation Models" (DEM) and "qualities of Digital Terrain Models".
Producing Digital Terrain Models
Usually the Digital Terrain Models (DTM) are provided by (e.g.) land surveying offices as basic data. We offer you to find the needed Digital Terrain Model if demanded (compare: "Services").
If you cannot find a suitable Digital Terrain Model for your special demands we can produce the one you need - just ask us. You do profit of our long year experience with Digital Terrain Models. Although we produce Digital Terrain Model using high quality interpolation methods the "quality" of the Digital Terrain Model is dependent on the basic data, like the isohypses out of topographic maps, laser scanning, etc. (see below).
Evaluating Digital Terrain Models
Before using the Digital Terrain Model as a basic answering your special questions you should clarify if the Digital Terrain Model meets your demands or which "quality" you can expect as a result of the evaluation of the Digital Terrain Model. For example the Digital Terrain Model with rounded altitude values (without correcting previously) is unqualified to answer hydrologic or pedologic questions.
Because of our long year experience with Digital Terrain Models of different origin and quality we are able to help you estimating the quality of the Digital Terrain Model. Our expert/scientific judgement to estimate the Digital Terrain Model (compare: "Services") is mainly aiming usage in Geo Sciences.
Correcting Digital Terrain Models
Although a wide range of Digital Terrain Models are offered the "quality" of the Digital Terrain Model is unfortunately often insufficient to geo scientific problems. The reasons as well as the faults vary. In many cases it is possible to take remedial measures. The following example demonstrates this using a Digital Terrain Model with "rounded altitude values":
Many user are not aware of Digital Terrain Models with "rounded altitude values" (for example: rounded off to an entire meter) being nearly useless in geo scientific practise (even in grid cell size: 100 m). The reasons are discussed in "Qualities of Digital Terrain Model" in "Criteria concerning the quality of using Digital Terrain Models in Geo Sciences and Geo-Ecology".
The following images show the effects of the "rounded altitude values" as well as our methods to modify:
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slope angle |
1) High quality Digital Terrain Model The images show maps concerning the slope gradients and the catchment areas based on a high quality Digital Terrain Model. Although the Digital Terrain Model with 12.5 m grid cell size and therefore absolute altitude- (height-) accuracy within cm (relative to the area of the grid cell being 156.25 m˛) does not meet the reality the relative altitude-exactness between neighbouring grid cells is relevant. This is demonstrated by the images (2) below. More comments concerning the images are at the end of this site. |
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2) Digital Terrain Model with rounded altitude values (up to an entire meter) After the altitude values of the Digital Terrain Model (1) were rounded off (entire meter) the image (on the left hand side) was produced to demonstrate the effect. Within the slope gradient it shows hills and valleys becoming a "pseudo terraced landscape". Hereby the inclination of the area is 0° and the aspect can not be calculated whereas there are hillside slopes/banks whenever the 'one-meter-jump' occurs. Especially within the catchment areas (as an important parameter in hydrological and pedological studies) the fault of the "pseudo-terraced landscapes" is distinct: literally the water stands still at the "Pseudo terraces". To simulate the run-off is impossible taking the inclination of 0° and not being able to determine the flow direction. Without showing further examples of the lowland you can easily imagine how disastrous this problem would turn out there. More comments concerning the images are at the end of this site. |
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slope angle |
3) Digital Terrain Model after correcting the rounded altitude values Although the "rounded altitude values" means irretrievable loss of information our method can "save" a Digital Terrain Model (with "rounded altitude values") for scientific needs. The images show the result of the corrected Digital Terrain Model of the images (2). Compared to the original Digital Terrain Model of image (1) it differs in detail. But it also shows the good approximation to the relations (proportions) of the real terrain. More comments concerning the images are at the end of this site. |
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catchment area |
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Comments concerning the images:
Section (7.5 x 7.5) of Lower Saxony (eastern foreland/piedmont of the "Göttinger Wald") Origin of the Digital Terrain Model: "DGM5", kindly provided by
"Landesvermessung + Geobasisinformation Niedersachsen (LGN)"
(being the surveying and geo base information office in Lower Saxony)
Grid cell size of the Digital Terrain Model: 12.5 m, meaning 601 x 601 grid cells in the section
The shown catchment areas are shaded; exaggeration of height: 4 times
