[Proj] vertical projection

[Vincent Mora]

Hi,

I need to draw terrain sections for several projects (hydrology, geology).

The vertical section is defined by a linestring in the (x,y) plane (e.g.
+proj=lcc). Data in the vicinity of the section are ortho-projected on
the folded plane with coordinates (s,z), where s is the point location
on the line (meters or feet).

For the moment the CRS part of the QGis plugin we are developping is a
bit of a hack, and I'd like to introduce that kind of projection in
proj4 since I believe it belongs there.

A projection on a folded plane is rather common, but in this case:
- the folds are sharp,
- the projection is not well defined for points that lie on the bisector
of two line-segments
- the projection is meaninigless for points that are not in the plane
vicinity.

The proj4 string should contain:
- the line definition (e.g. +wkt=LINESTRING(...))
- the classical definition of the CRS of the line,
- and a thickness (vicinity of the plane)

Questions:
- has such a CRS it's place in proj4 ?
- do you see obvious errors/misconceptions ?

Cheers,

V.



Some details here
<https://github.com/vmora/qgis_section/blob/master/docs/source/design.rst>
along with the current implementation of section in a QGis plugin.