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arc gis期末复习考点第十四章

Chapter 14 Review Questions

1. Describe the two common types of data for terrain mapping and analysis. Digital elevation models (DEMs) and triangulated irregular networks (TINs) are the two common types of data for terrain mapping and analysis. A DEM represents a regular array of elevation points. A TIN approximates the land surface with a series of nonoverlapping triangles.

2. Describe level-2 DEMs from the USGS in terms of point spacing and vertical accuracy.

Level-2 DEMs are available at a spacing of 30 meters or 10 meters. Their accuracy has a maximum RMS error of one-half the contour interval.

3. USGS DEMs are known to contain relative errors. What are relative errors? Relative errors are local but significant errors relative to the neighboring elevations.

4. List the types of data that can be used to compile an initial TIN.

Typically a DEM is used to compile an initial TIN. But other data sources such as LIDAR data, surveyed elevation points, and contour lines can also be used.

5. List the types of data that can be used to modify a TIN.

Point data: surveyed elevation points, GPS (global positioning system) data, and LIDAR data.

Line data: contour lines and breaklines (line features representing changes of the land surface such as streams, shorelines, ridges, and roads).

Area data: lakes and reservoirs.

6. The maximum z-tolerance algorithm is an algorithm used by ArcGIS for converting a DEM into a TIN. Explain how the algorithm works.

The maximum z-tolerance algorithm selects points from an elevation raster to construct a TIN such that, for every point in the elevation raster, the difference

between the original elevation and the estimated elevation from the TIN is within the specified maximum z-tolerance.

7. Suppose you are given a DEM to make a contour map. The elevation readings in the DEM range from 856 to 1324 meters. If you were to use 900 as the base contour and 100 as the contour intervals, what contour lines would be on the map?

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