Definition of Computational Error
- If (X, Y, Z) is the true value of a point, and (XA, YA, ZA) the approximate
- Use the Euclidean metric E2 = [(X- XA)2 + (Y- YA)2 + (Z- ZA)2] to determine an error ball of radius E; for two dimensional systems, set the Zs to 0.
- There two types of geodetic points: (lat, lon, h) or for the map projections
- Need to interpret angular errors as position errors.
- Except for TM, the forward transformations are exact.
- Generate a known set of points {(lat, lon, h)}.
- When the exact transformation is available, generate the corresponding
exact set of points {(X, Y, Z)} using the simple known conversions.
- E, in terms of position errors, can be calculated in two or three dimensions.
- Because there is no exact transformation in either direction.
- Angular measures can be converted to distance measures using s = r•ø.
• For other projections angular errors also need to be converted to distance errors.