the Bertin 1953 projection #1133
Conversation
There was a problem hiding this comment.
Thanks for opening this PR.
I have added some inline comments which I think will improve the quality of this PR. In addition I a few general comments/changes I'd like to see before this gets merged:
- We need tests.
- I'd prefer if the code didn't use camelCase variable names. Generally speaking (there are exceptions), PROJ uses snake_case.
I would like to see a more formal mathematical description of this projection. As I understand it, the projection is basically the Hammer projected subjected to a rotation and some inital warping. I'd be interested to see if we couldn't to the same thing by constructing a pipeline of some more basic operations. This is just me thinking aloud, not something that should be pursued in this PR :-)
| Further reading | ||
| ################################################################################ | ||
|
|
||
| #. Philippe Rivière (2017). `Bertin Projection (1953) <https://visionscarto.net/bertin-projection-1953>`, Visionscarto.net. |
There was a problem hiding this comment.
Is this the best reference we have? If possible, I'd like to have a reference to the mathematical description as well, preferably an academic paper.
There was a problem hiding this comment.
Well if you read that modest blog post, you'll know :)
(I wish I had time and resources to publish this as an academic paper.)
There was a problem hiding this comment.
I did, but it wasn't clear to me if something else was published.
You are welcome to use the PROJ docs as a platform for describing the mathematics behind the projection.
There was a problem hiding this comment.
PS: I agree that my construction is totally ad-hoc, and that another formula might be much nicer mathematically (esp. with second and third derivatives). It's the best I could come up with as a first approximation, and I'm very open to making an upgraded formula at some point (provided it still respects the original drawing).
| phi -= 0.8 * d * sin(phi + M_PI / 2.); | ||
| } | ||
|
|
||
| /* Project with Hammer (1.68,2) */ |
There was a problem hiding this comment.
So this is the same Hammer projection as defined in PJ_hammer.c, yes? Why not use that directly by instantiating a Hammer specific PJ object with Q->P_hammer = proj_create(P->ctx, '+proj=hammer ...') in the projection setup and call pj_fwd(Q->P_hammer, lp) here?
This avoids duplicate code and potential bugs in Hammer will be fixed both places if necessary.
There was a problem hiding this comment.
Yes I wanted to do that, but couldn't find an example in the src/
There was a problem hiding this comment.
Something similar is done in PJ_deformationc.:
You'll have to adjust it a bit but the general idea is there. Also notice that you need to create a custom descructor for the PJ object. There's an example for that in the same file as well.
There was a problem hiding this comment.
Feel free to add this! It's my first contribution to Proj.4 and it had been a looong time since I coded anything in C :-)
- classification - tests - coding style
|
thank you! |
closes #1120