[PROJ] Is your the geoid model from your country in PROJ?

[Howard Butler]

> On Apr 12, 2024, at 5:56 AM, Javier Jimenez Shaw via PROJ <proj at lists.osgeo.org> wrote:
> 
> Maybe you want to talk with your local agency to fix this ;)

It is not always clear as a motivated-but-unconnected individual which local agency and person inside it to contact to sort things out. It is also often the case that some government officials might not feel they have the power to change the license or releasability of a model. Finally, getting an official grid to PROJ CDN might require navigation of the procedures of a specialized geospatial standard body (EPSG) and standards conformance of those grids before official registration. 

A step-by-step process document written by people who have completed it would be a helpful guide of all the various starting points and steps. 

> Mainly local companies and surveyors will have an easy workflow if the needed geoid model is really easy to use, better if it is automatic in their tools.

As a frequent user of grid transformations in PROJ, I do not fondly remember the days before PROJ_NETWORK. It is very powerful for PROJ to be able to conveniently compute its best transformation, apply it to the data with very little manual intervention, and not require the management of gigabytes of grid content to do it. By making it possible and convenient to be more precise, many software and tools across the PROJ-using dependency graph have benefitted greatly.

Even's COG-based GTG [1] approach for PROJ supports both an incremental network and a local cache distribution model at the same time. I've found it frustrating the OGC CRS Standards Working Group didn't value a similar approach when it developed the GGXF standard. Not only is GGXF content going to require yet another transformation for use as an incremental network, its complexity in comparison to GTG is going to be challenging for grid producers. 

I suspect GTG's simpler model for grid producers and PROJ_NETWORK's distribution channel for grid consumers will close the loop for many. The challenge is one is labeled a standard but has no? public software implementations, while the other one is unlabeled but has four years of implementation experience in a widely used open source software. Maybe there are some in the community who would support bringing GTG forward as an OGC Community Standard if such a label is important to them.

[1] https://proj.org/en/latest/specifications/geodetictiffgrids.html