The Chaining Problem
A chain of routines is often used to get from one SRF to another. For example to get from CC to UTM, one first transforms CC to CD and then transforms CD to UTM (separate procedure calls)
Some users want to go directly from CC to UTM without calling CC to CD, i.e., they want a single routine that transforms CC to UTM – this is a chain
- There are a 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 CC, 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