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lack of support for South African projections #18
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Comment by neteler on 2 Jun 2009 21:05 UTC Testing in GRASS:
But the definition seems to be known by GeoTIFF: and is also listed in this file The Schwarzeck datum is described here: http://www.mme.gov.na/gsn/nam-map-system.htm:
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Comment by craigleat on 31 Jan 2010 19:45 UTC |
Comment by warmerdam on 1 Mar 2010 04:46 UTC |
Comment by warmerdam on 1 Mar 2010 21:07 UTC However, EPSG PCSs using TMSO (2046-2055, 22275-22293, and 29371-29385) all seem to use a false easting and northing of zero so the issue does not have an effect. If there is an issue we need to ensure that TMSO translation to proj=tmerc for proj.4 also negate the fe/fn values which it does not do now. |
Comment by craigleat on 2 Mar 2010 09:41 UTC
In my experience it is only land surveyors and engineers that use non zero false westings and southings. I have a number of dwg/dxf files using these offsets. Currently I translate (shift) the data inside the CAD app to remove the offsets and then export to a GIS format. For me it would be useful to have correct signs applied to the fw/fs values. |
Comment by warmerdam on 31 Jul 2010 14:43 UTC This ticket remains open only in the hopes of addressing the sign of false easting/northing issue. |
Comment by cyberworldukltd on 2 Feb 2012 06:52 UTC |
Comment by gfleming on 31 Aug 2013 14:46 UTC In the current implementation only the y value is being negated whereas both coordinates must be negated AND swap axes such that x => -y and y => -x. Refer to the attached 'south-oriented_TM_coords.csv'. To get it to draw correctly in QGIS 2.0 in EPSG:22287 CRS you have to swap the X and Y column headers. It is in north west Lesotho. |
Comment by warmerdam on 31 Aug 2013 15:18 UTC Could you give me a couple points in EPSG:22287 and what they ought to be in WGS84? |
Comment by gfleming on 1 Sep 2013 15:33 UTC If north-facing coordinates are defined by +axis=enu then the official South African TMSO CRS ("LO") should simply be +axis=swu and not +axis=wsu. I'm struggling to test this in QGIS now because of http://hub.qgis.org/issues/8487. If this is the case then all that needs to be changed is the +axis flag in all the "LO" definitions (odd numbers in 22293 and all numbers in 2055) |
Comment by warmerdam on 3 Sep 2013 02:01 UTC I have reviewed the EPSG 22287 description as reported in the Galdos produced EPSG registry web site. Unfortunately, it seems impossible to get a direct url to a report due to loads of javascript bullshit (I fondly remember when the web was html documents with urls!). However, I have attached an html capture of the report page which unfortunately Trac won't render nicely. The gist of it is that EPSG claims EPSG 22287 is supposed to be westing for the first coordinate axis, and southing for the second. I believe that the PROJ.4 definitions is created based on that. Of course, it isn't uncommon for folks not to necessarily honour the EPSG axis orders (ie. for EPSG:4326) but I'm not sure how I can know when I should or shouldn't do so. If you can give me a strong assurance that the order should be reversed for essentially all gis use of 22287 and similar PCS codes the I can introduce an override though I just hate doing that. I do agree that the issue is likely around creation of the PROJ.4 init strings from EPSG's dictionary rather than being breakage in the core PROJ.4 engine. |
Comment by gfleming on 3 Sep 2013 11:30 UTC As per http://trac.osgeo.org/proj/wiki/TMSO
and other discussion and references on that page, incl http://www.dwa.gov.za/iwqs/gauss/node7.html#SECTION00025000000000000000, I guess it depends on how the coordinates are ordered in the original geometry. I've attached test_TMSO_axis orientation.csv above to do some testing. What I call 2050_reversed should actually be 2050 according to the EPSG. But according to South African convention as I am familiar with it, what I call 2050 is how we work with TMSO. i.e. we reverse the EPSG axis ordering convention. But I will do a snap survey to confirm this before we jump to conclusions. And we should probably check how ESRI and others handle it so it's consistent. |
Comment by gfleming on 29 Sep 2013 12:39 UTC
Based on feedback from the community in SA I think we can lay this to rest: EPSG and proj.4 do define and implement the SA south-facing CRS correctly. Surveyors do use +axis=wsu. GIS practitioners just need to remember to ensure that the coordinate order matches; as you say, some people don't honour EPSG axis orders and use x,y when they should be using y,x (since the South African surveyors' westing is y and southing is x). |
Attachment added by gfleming on 17 Oct 2008 09:00 UTC |
Attachment added by gfleming on 17 Oct 2008 09:00 UTC |
Attachment added by gfleming on 30 Aug 2013 04:39 UTC |
Attachment added by gfleming on 1 Sep 2013 06:28 UTC |
Attachment added by warmerdam on 3 Sep 2013 01:56 UTC |
Attachment added by gfleming on 3 Sep 2013 11:08 UTC |
Reported by gfleming on 17 Oct 2008 08:59 UTC
South African Coordinate System zone xx (EPSG odd numbers from 22275 - 22293)
and
Hartebeesthoek94/ Loxx (EPSG 2046 - 2055)
are not supported / do not have standard definitions in proj4. South Africa users of proj4, QGIS, PostGIS and others are thus crippled.
Attached are the WKT and PROJ4 definitions as csvs from PostGIS spatial_ref_sys.
SA Hartebeesthoek datum.csv:
4148 is fine - that's the fundamental GEOGCS. The rest have default, invalid proj4 definitions, except for 2054 (the last one) where I have attempted a proj4 definition but I dont think its quite right - it doesn't work.
SA Cape datum.csv:
The proj4 definitions for the SA Cape datum projections are INCOMPLETE. They only include the datum specs, not the projection or central meridian or other parameters.
Apparently the problem is that proj4 does not support 'transverse_mercator_south_orientated'?
Migrated-From: https://trac.osgeo.org/proj/ticket/18
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