use authid instead of proj.4 strings

[jef]

Currently we try to use the proj.4 strings to store references to coordinate systems (eg. for the default project crs). Unfortunately the proj.4 string isn't unique in our database:

sqlite> select count(*),parameters from tbl_srs group by parameters order by count(*) desc limit 10;
54|+proj=longlat +ellps=intl +no_defs
27|+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs
21|+proj=longlat +ellps=clrk80 +no_defs
17|+proj=longlat +ellps=bessel +no_defs
15|+proj=longlat +ellps=clrk66 +no_defs
13|+proj=longlat +a=6378249.2 +b=6356515 +no_defs
11|+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs
9|+proj=longlat +ellps=GRS80 +no_defs
9|+proj=longlat +ellps=krass +no_defs
9|+proj=tmerc +lat_0=0 +lon_0=105 +k=1 +x_0=500000 +y_0=0 +ellps=krass +units=m +no_defs
sqlite> select auth_name,auth_id,description,parameters from tbl_srs where parameters='+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs' limit 1;
EPSG|4148|Hartebeesthoek94|+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

So selecting 'EPSG:4326' as default CRS results in 'EPSG:4148 - Hartebeesthoek94' - which obviously is irritating.

The attached patch switches to the use of authid instead of proj.4 strings. Any objections to commit it for 1.7?

[jef]

use authid instead of proj.4 strings to identify CRS

[mhugent]

Looks good to me. +1 for commit.

Marco

[borysiasty]

I've slightly modified your patch:

1. Also save the authid to QSettings, not only read ;-) (qgsoptions.cpp 642 and 646)

2. Use layerDefaultCrs Qsettings key instead of misleading defaultCrs. As the patch breaks this setting anyway, I take a opportunity to clean up a bit. (qgsoptions.cpp 191 and 642; qgisapp.cpp 361)

By the way. Seems it works not only with epsg ids. Is the note in api doc out of date? ​http://doc.qgis.org/head/classQgsCoordinateReferenceSystem.html#5789a11684af1415ffc74d7ce9ab91f0

[borysiasty]

small modifications

[jef]

Replying to borysiasty:

1. Also save the authid to QSettings, not only read ;-) (qgsoptions.cpp 642 and 646)

if you insist ;)

By the way. Seems it works not only with epsg ids. Is the note in api doc out of date? ​http://doc.qgis.org/head/classQgsCoordinateReferenceSystem.html#5789a11684af1415ffc74d7ce9ab91f0

Oh, yes. That note was probably already there, when we added the auth_name column to tbl_srs...

[jef]

applied in r15419.

[borysiasty]

But what with project files? Both authid and proj string are saved.

JEF, could you please confirm that authid is higher prriority and hopefully close the ticket again?

[jef]

Replying to borysiasty:

But what with project files? Both authid and proj string are saved.

JEF, could you please confirm that authid is higher prriority and hopefully close the ticket again?

looks like it. order is authid, epsg, proj.4 and as last resort a CRS initialized with all the values from the node. Otherwise we should have hit the 'Hartebeesthoek94' problem earlier...