Swissgrid CH1903 is off by up to 3 meters (does not use data set of local corrections )

[bastiK]

To calculate CH1903, 2 steps are required:

(1) WSG84 -> CH1903+ (using a formula)

(2) CH1903+ -> CH1903 (using a grid / triangulation file)

Step (1) if fully implemented. However step (2) is missing. It introduces corrections of up to 3 meters (plus false easting/northing of 2000000/1000000) and accounts for the historical deviations from the modern system.

To fix this, we could:

• Use the "official" triangulation file and FINELTRA algorithm.
• Use the NTv2 grid file provided by swisstopo. This is an approximation, but should be in general good enough for osm use.

Link:
​http://www.swisstopo.admin.ch/internet/swisstopo/en/home/products/software/products/chenyx06.html

[bastiK]

see also #5327

[bastiK]

triagulation data (binary format)

[bastiK]

On the swisstopo website only NTv2 grid is available, but the link to the triangulation file is dead.

I sent an email to swisstopo and received the file in binary format. (The link is still not working.)

[bastiK]

@sbrunner: Do you like to pursue this? I haven't found any documentation on the low-level format of the binary file.

[sbrunner]

Hi,

Yes, I plan to see what is possible to do but not right now, (actually I'm working on better support of OSM file format in OpenLayers ;-) )

CU, Stéphane

[bastiK]

Ok, if you are able to decipher the binary format, let me know!

Sebastian

[Don-vip]

Ticket #8949 has been marked as a duplicate of this ticket.

[Don-vip]

There is now a free official Java library on Swisstopo website: ​https://shop.swisstopo.admin.ch/fr/products/geo_software/DLL_info

[Don-vip]

I started to play with the library (see attached jar, developer manual and not-working patch) but can't find the correct usage. bastiK can you please help me? :)

[bastiK]

I think you should convert to military LV03 (EPSG:21781) and not the civil which is no longer in use.

[bastiK]

They do have a download for the NTv2 grid file by now, so no extra code or library is needed. I couldn't find appropriate terms and on the current side, but ​this offer should still apply. This means The conditions are similar to those of the other grid files we distribute.

[Don-vip]

Ah, even better. Do we need the two NTv2 grids or only one?

Concerning the license it seems OK, to be sure we can include it in the SVN as the URLs are not stable. Even if not strictly required, we can also apply the first ​licence for free geodata obligation:

To add a clearly visible source reference with the following wording whenever geodata are published or passed on: “Source: Swiss Federal Office of Topography” (Article 30, Geoinformation Ordinance);

[bastiK]

The one labelled "NTv2 grid ETRF93/ETRS89 -> CH1903/LV95" should be enough to add full EPSG:21781 support. (I think CH1903/LV95 is a typo and they mean CH1903/LV03.)

It works with the cs2cs tools, so there should be no problem in JOSM:

$ echo "601000.0 197500.0 555.0" | cs2cs +proj=somerc +lat_0=46.95240555555556 +lon_0=7.439583333333333 +x_0=600000 +y_0=200000 +ellps=bessel +nadgrids=./CHENYX06_etrs.gsb +to +proj=lonlat +datum=WGS84
7d27'6.35"E	46d55'42.94"N 555.000

How do you plan to make the file available to the user as its 3 MB?

[Don-vip]

Good question. I think it would be worth to implement a NTV2 file management as official JOSM extension. If the default JOSM jar does not contain the required NTV2 files, the first time a user chooses a projection that requires ones, the grid is downloaded from JOSM server and stored in JOSM cache directory.

We could also still build a bigger jar file containing all grids for users who need JOSM to remain fully operational without Internet access.

@team: what you do think?

[stoecker]

Sounds like a good idea and makes the JAR smaller.

[Don-vip]

OK. I will first try to implement this system with existing NTV2 grids through #14422 before adding the Swiss grid.

[bastiK]

+1

[Don-vip]

I have sent an e-mail to SwissTopo to ask them clarifications about the redistribution/licence. I hope the grids will then be included into ​proj.4 as well.

[bastiK]

Aren't they already? What is missing from proj.4 is the German BETA2007.gsb.

[Don-vip]

Replying to bastiK:

Aren't they already?

No, see ​here.

What is missing from proj.4 is the German BETA2007.gsb.

Can you please create a ticket or even a PR? I'm not familiar with this one ;)

[sebastic]

The PROJ.4 documentation lists most common national grids, see:

​http://proj4.org/grids.html

[Don-vip]

#14422 was a lot easier than I thought :)

[bastiK]

Replying to Don-vip:

Replying to bastiK:

Aren't they already?

No, see ​here.

What is missing from proj.4 is the German BETA2007.gsb.

Okay, I falsely assumed the content of the proj-data Debian package is the same as what is in the proj.4 repository. Apparently the debian maintainer add the Swiss grid file when the package is built.

Can you please create a ticket or even a PR? I'm not familiar with this one ;)

I've sent an email to the contact person of the German agency to clarify the usage terms.

[Don-vip]

In 11660/josm:

see #5399 - Swissgrid: add NTv2 grid file provided by swisstopo

[Don-vip]

ProjectionRefTest needs an update but I cannot do it :(

[bastiK]

In 11661/josm:

see #5399 - update ProjectionRefTest

[bastiK]

Replying to Don-vip:

ProjectionRefTest needs an update but I cannot do it :(

I hoped others would be able to update it too ...

[Don-vip]

Thanks! I tried but cs2cs always replied "* *" and I didn't understand why.

[bastiK]

Maybe works now with changes from [11661] (try again next time...).

[Don-vip]

Replying to bastiK:

Maybe works now with changes from [11661] (try again next time...).

I tried again in order to add ESRI projections (#15880) and it works!