[MetaCRS] A Question About The Typical Method Of CRS Transformations

[Landon Blake]

I had a question about the typical method used by existing CRS code in
different projects to perform transformations from one CRS to another.

 

Does most code search for the definition of a transformation algorithm,
with no real knowledge of the projection geometry of the source and
destination CRS, to perform the transformation?

 

Or does most code, on the contrary, use knowledge of the projection
geometry of the source and destination CRS to determine the
transformation algorithm on its own?

 

I imagine there are distinct advantages and disadvantages to each
approach. As an example, in the first scenario I might leave CRS
definitions out of the picture altogether, and instead implement a
system in which support for a CRS was added by a single programming
interface that performed transformations to and from the subject CRS and
a pivot CRS. In this scenario the CRS code performing the transformation
would need almost no knowledge of the subject CRS, all of the burden
would be placed on the person implementing the programming interface.

 

In the second scenario I eliminate the programming interface altogether,
and I place all of the emphasis on the definition of the subject CRS. I
then place logic in the CRS code that performs the correct
transformation operations based on the parameters in the definition. (I
do these three (3) steps for a cylindrical projection, while I do these
five (5) steps for a conical projection.)

 

I'd think the first scenario is the easiest to program, but the most
difficult to add CRS definitions too. (To add a definition would require
knowledge of the particular programming language used to implement the
library.)

 

In the second scenario the CRS code would be more complex, but a CRS
definition could be added with a simple text file.

 

Are there any thoughts on which approach is superior? Which approach is
used by existing CRS solutions?

 

Is a hybrid approach possible?

 

Landon

 

 

 



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