#3362 closed defect (fixed)
gcs.override.csv has wrong datum shift for Belge 1972
Reported by: | mikrit | Owned by: | warmerdam |
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Priority: | normal | Milestone: | |
Component: | OGR_SRS | Version: | unspecified |
Severity: | normal | Keywords: | datum shift |
Cc: |
Description
The file
http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/gcs.override.csv
contains the lines
# From Jan: http://bugzilla.remotesensing.org/show_bug.cgi?id=1336 # 4313,Belge 1972, [- stuff deleted -] ,9606,106.868628,-52.297783,103.723893,-0.336570,0.456955,-1.842183,1.0000012747
However, this is wrong. The error can be 190 meters (at least). The correct line should end with
... ,9607,-106.8686,52.2978,-103.7239,-0.3366,0.457,-1.8422,-1.2747
For more details, see http://trac.osgeo.org/proj/ticket/65 and http://lists.maptools.org/pipermail/proj/2010-January/thread.html
Best regards,
Change History (7)
comment:1 by , 14 years ago
Component: | default → OGR_SRS |
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Keywords: | datum shift added |
Status: | new → assigned |
comment:2 by , 14 years ago
Yes, I used a Belgian converter tool, downloaded via http://www.ngi.be/FR/FR4-4.shtm , to obtain the following test point in west Belgium:
WGS84: 2°30' E, 51° N
Belge 1972: 2°30'04.37266" E, 50°59'58.09273" N
Actually, I am not quite sure whether I made the tool to use the 7-parameter shift or some grid shift file. But the standard deviation between the two possibilities is supposed to be only 0.2 meters.
(And strictly speaking, the 2°30' E, 51° N coordinates are really ETRS89 instead of WGS84. But the differences are mainly caused by the continental drift since 1989.)
comment:3 by , 14 years ago
Hmm, I tried this test point with what I now believe to be the correct parameters and I did not get the expected values:
cs2cs +proj=longlat +ellps=WGS84 +datum=WGS84 +to \ +proj=longlat +ellps=intl +towgs84=-106.869,52.2978,-103.724,0.3366,-0.457,1.8422,1.2747 \ +no_defs -2.5 51 2d30'3.846"W 51d0'1.824"N -54.814
Any thoughts on why this might not be giving the expected results?
comment:4 by , 14 years ago
You've got the parameters right - as far as I can see - but you prepended a minus sign to the test point longitude. I guess it comes automatic when you live on the western hemisphere.
By the way, you can find test points for European datums on http://www.crs-geo.eu , although the site it a bit awkward to navigate. Go to "CRS Description", then go to "national CRS", then go to "Belgium", then on row BE_BD72 / LAMB72, click the link in the column "Descr. of Transf." (which gives a somewhat older datum shift, by the way), then scroll down to the bottom and go to "Verification Data".
comment:5 by , 14 years ago
Resolution: | → fixed |
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Status: | assigned → closed |
Hmm, with the correct direction for East, I get:
2.5 51 2d29'55.627"E 51d0'1.909"N -57.688
Still not very close to what you quote as correct results, and going in the wrong direction.
Using the first test point from the verification data on the site you mention:
BE_BD72 (DMS) ETRS89 (DMS) ------------------------------------------------------------------ Lat Lon (E is +) Lat Lon (E is +) ------------------------------------------------------------------ 51 6 40.6800 3 3 28.4400 51 6 38.77 3 3 32.87 49 41 38.0400 5 38 29.7600 49 41 35.94 5 38 34.38
I get:
input: 3d3'32.87 51d6'38.77 output: 3d3'28.434"E 51d6'40.678"N -57.899
which is accurate to a small fraction of a second (treating WGS84==ETRS89). So I suppose the result is ok.
comment:6 by , 14 years ago
Oops, I'm sorry. I confused WGS84 and BD72 when I reported my test point above. It is the point 2°30' E, 51° N that is in BD72, and the point 2°30'04.37266" E, 50°59'58.09273" N is in WGS84. ( See http://lists.maptools.org/pipermail/proj/2010-January/005030.html )
comment:7 by , 14 years ago
OK, I'm gettinggood agreement now.
2.5 51 2d30'4.373"E 50d59'58.091"N 57.690
This is really a libgeotiff issue. I have committed http://trac.osgeo.org/geotiff/changeset/1801 with the suggested change.
I would like to have a test point in this GCS and it's corresponding WGS84 point that I could add to a test suite. Could you please supply one?