Accuracy of a DEM can be evaluated by comparing DEM derived elevation values with actual elevation
values, called as refrence data that can be acquired with high precision field survey or a secondary source (Castrignano et al., 2006).
We want our altimeters to read the actual elevation
, so at that airport we want the altimeter to read 1000 feet.
Also, there are numbers on some of the lines showing the actual elevation
. By studying the numbered lines, you can easily tell which direction the slopes lay.
By using his barometer and sextant he calculated the elevation of Roche Miette at 7,300 feet, just 300 feet short of its actual elevation
. (34) At the other extreme, he overestimated, using triangulation, the elevation of Mount Murchison by about 5,000 feet.
While arguably acceptable for windstorm or earthquake risk analyses, such variances can result in substantial differences between the property's assumed and actual elevation
, making reliable flood risk assessment impossible.
Let r be the actual elevation
of the dish with respect to the earth's horizon and let c be the desired elevation of the dish as it follows the star.
However, increases in Lake Michigan will cause the regional groundwater table and other linked groundwater tables to rise, thus the actual elevation
in the captured lake may not correspond with Lake Michigan's, but the relative changes should.
Scientists can determine the actual elevation
within 4.5 centimeters (1.8 inches) thanks to satellites carrying radar altimeters.
An option is a laser receipt sensor that informs the driller, in real time, the actual elevation
of the hole, allowing drilling to stop at a predetermined depth.
Experimentation in the field suggested that with care we could reliably hold the tape to within one-third degree of level by eye over a distance of five meters, so our results probably did not underestimate the actual elevation
With every fifth line, the actual elevation
appears so you can tell whether you are looking at a valley or a ridge.
Hub Elevation: Actual elevation
of the top of a hub in feet, tenths and hundredths of feet.