The Chaining Problem
A chain of routines is often used to get from one SRF to another. For example to get from GC to UTM one first transforms GC to GD and then transforms GD to UTM (separate procedure calls)
Some users want to go directly from GC to UTM without calling GC to GD. That is, they want a single routine that transforms GC to UTM. This is a chain.
- There area large number of possible chains between all SEDRIS spatial reference frameworks. There are also technical issues.
Such chains are attractive because many intermediate calculations can be cached for use further along in the chain and only one function call is required.
A common test is to transform a point from UTM to GC and then inverting the process to �prove� transitivity.
- Such a process can fail the transitivity test for points near a UTM zone boundary in that the point starts in one zone and ends up in another.
- This is due to a combination of round-off error and truncation error accumulation.
Caution must be exercised by the user in such cases. Chains must be designed to insure transitivity.