Data structures for representing topography

Question 1

What are DEMs?

Answer 1

Digital elevation models

• z value for each raster cell. based on regularly spaced height observations that model topographic surface
• sampling interval is determined by terrain characteristics & file size restrictions

Question 2

How can we represent topography with vector?

Answer 2

• isolines- lines that connect points of equal value (i.e. contour lines-lines of equal elevation, or isotherms-lines of equal temperature)
• from TIN (TINs from Delaunay triangles)

Question 3

explain terrains

Answer 3

• newer multi-resolution triangulated surface
• stored in geoDBs
• scaleable-billions of points supported

Question 4

What is LIDAR?

Answer 4

• light detection and ranging
• laser pulses sent from receiver.
• airborne or terrestrial
• multiple returns (many, many points)
• accuracy depends on (laser ranging accuracy, GPS error)
• usually, x,y accuracy in sub-meter range. z accuracy around 10 cm