Save .proj4 strings used for georeferencation

[dg0yt]

mlerjen reported on Sourceforge [tickets:#489]:

It would be comfortable to have the few .proj4 I most often use directly available when creating a new map. That way one only would have to look up these strings if mapping in a new reference system. My preference would be a combined enter/drop-down field to enter the reference specification, with the ones used before as drop-down-menu options.

[dg0yt]

• Milestone: 0.6.0 --> 1.0

[dg0yt]

Collecting the strings locally is a valid request. But it is only one option (and probably easy to simulate if you know how to use Proj's init files). You may also report particular configurations with name and country/region here if you think that they are common. We can add new coordinate reference systems easily without breaking things.

[dg0yt]

krticka posted on Sourceforge:

Yes, this would be useful, especially for beginners. Show whole CRS name and EPSG code in list, there can be several variants of the CRS.
So, please add into list most used Czech system S-JTSK / Krovak East North (EPSG: 5514)
Proj4 specification:
+proj=krovak +lat_0=49.5 +lon_0=24.83333333333333 +alpha=30.28813972222222 +k=0.9999 +x_0=0 +y_0=0 +ellps=bessel +pm=greenwich +units=m +no_defs +towgs84=570.8,85.7,462.8,4.998,1.587,5.261,3.56

Thank you!

[M0OJM]

Please add Ordnance Survey GB
+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs

[dg0yt]

@M0OJM Is there an EPSG number for this?

[mpickering]

I believe it is 27700?

[M0OJM]

There is a more accurate transformation for OSGB called OSTN02 but not sure if it is easy to implement. Explained here https://digimap.edina.ac.uk/webhelp/digimapgis/projections_and_transformations/transformations_in_gdalogr.htm
This seems the key bit
2) Unzip and put the gsb file into the ‘projlib’ folder in the GDAL installation (or somewhere else but you will need to specify the location).

[dg0yt]

into the ‘projlib’ folder in the GDAL installation

This would be the proj folder in the Windows package, and Resources\proj on macOS, for Mapper.
If you want, you might create a personal file next to the exisiting files, and use it as custom PROJ.4 spec in a simplified way: +init=personal:12345. On a mapper update, you would just copy this file to the new installation.

BTW, proj.4 might be upgraded from 4.9.3 to 5.0.1 with the next release. Proj development is moving very well. They already provide more data then we bundle ATM.

[M0OJM]

Hi Kai
Thanks for your help but as this is new to me I am having difficulty understanding some of your comments.

1. Selecting CRS as 'by EPSG code' and '27700' seems to do the same as Proj.4 with the string I provided. If I then select CRS 'Proj.4' it shows Specification as +init=epsg:27700
   I note the epsg file already contains an entry '27700 British National Grid'. To make it the default do I need to create a personal text file with a name of my choosing? If so, does it just contain the text +init=epsg:27700 ? I also note that the world file contains list of several proj +init references including <bng> # British National Grid.
2. I have placed the OSTNS2_NTv2.gsb file in the proj folder. I assume that it requires something more complicated to make OOM use it. It appears that it only improves the accuracy by 0.5m so it's not a problem if I can't get it to work.
   John

[dg0yt]

Hi John, these are alternative options when you edit a map's georeferencing:

• Just use 'by EPSG code' : '27700'. This is what will also be supported by OCD export soon.
• Copy the OSTN02 file and enter the full PROJ.4 specification as given in the linked page.
• For convenient use of the OSTN02 file, put in the full specification in a PROJ.4 file (e.g. personal) and just refer to that file (+init=personal:12345) where personal is the name of the file and 12345 is the code number which identifies the specification within the file. (The file needs to use the same syntax as epsg etc.)
  I just recommend against editing the existing PROJ.4 files. This would create confusion when reporting bugs, and changes are prone to be lost on updates.

There is no way to set a default georeferencing (for new maps) at the moment.