[PROJ] Swiss geoid file (now free)

[Javier Jimenez Shaw]

Hi all

Since March 1st 2021, Swisstopo makes all their products "free of charge
and for open access use":
https://www.swisstopo.admin.ch/en/swisstopo/free-geodata.html (for French,
German or Italian native speakers, select your preferred official version).

That includes the Geoid file for CHGeo2004.

I was considering to include it in PROJ-data via PR. Before doing that I
have some questions:

-- License --
I do not know if their definition of the free access is enough for PROJ
requirements. In that page, in 'Frequently Asked Questions (FAQ)', in
question 'Under what licence is the geodata supplied by swisstopo?' they
say:

*swisstopo geodata is supplied with conditions of use which comply with the
legal basis. The conditions of use enable free use for all purposes and
oblige the user to indicate the source as “Source: Federal Office of
Topography swisstopo” or “© swisstopo”.*

In https://www.swisstopo.admin.ch/en/home/meta/conditions/geodata/ogd.html
the say as well:

*The free geodata and geoservices of swisstopo may be used, distributed and
made accessible. Furthermore, they may be enriched and processed and also
used commercially.*

Should I move forward? Is that enough for PROJ?

-- Source CRS --
The geoid file is provided in
https://www.swisstopo.admin.ch/en/knowledge-facts/surveying-geodesy/geoid.html
in 4 different "flavors": LV95/LHN95, LV95/LN02, ETRS89/LHN95, ETRS89/LN02
(I will now concentrate on LHN95, as LN02 is older).

LV95 (short version of "CH1903+ / LV95") is a projected CRS (EPSG:2056).
The geographic system "under" it is CH1903+ (EPSG:4150)
I was expecting a version like "CH1903+/LHN95" (the Swiss geographic CRS
with the Swiss vertical CRS), but there is not AFAIK.

What should we include in PROJ-data?
a) ETRS89/LHN95
b) LV95/LHN95
c) CH1903+/LHN95 computed from LV95/LHN95
d) something else
e) multiple of the above

Note that there are already two Swiss horizontal grids in PROJ-data:
"CH1903 (EPSG:4149) to CH1903+ (EPSG:4150)" and "CH1903 (EPSG:4149) to
ETRS89 (EPSG:4258)"

-- Transformation --
There is no such a transformation in EPSG like "ETRS89 to LHN95 height" or
"LV95 to LHN95 height" or "CH1903+ to LHN95 height". I was considering
asking Swisstopo to "create" them (via a proper EPSG request), but, which
one(s)? (this is probably related to the previous question, I guess).

In case they do not consider including themselves the transformation in
EPSG, should we create one as PROJ auth_name? Which one(s)?

Thank you.
.___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.
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