Ground rules for spatial operations algorithm development (cont’d)
- algorithms for computing SOs should be designed for the context in
which they are used. SO algorithms are usually not employed in isolation.
Many SO computations are followed immediately by several more to
form what is called a chain.
- all variables needed for the chain should be retained for subsequent use,
- designing for context may determine which of several procedures is
Example for an ERM: Some algorithms for converting geocentric
coordinates to geodetic naturally compute the trigonometric functions of
latitude and the radius of curvature in the prime vertical to full accuracy
as part of the process. If this conversion is followed by a transformation
to a map projection these variables will be needed. A good design for the
first conversion will retain them. On the other hand some popular
algorithms for the first conversion do not naturally produce these
variables and to get them require more relatively expensive calculations.
This should influence the choice of algorithm.