[postgis-users] transform() does not do work for NGO1948 zone III-> WGS84 longlat (epsg:27393->epsg:4326)

Tue Jan 3 10:55:36 PST 2006

Just to close this...

I have tested some more, and it seems as if transform() in
PostGIS 1.0.x is working as expected. When I changed +lon_0
in proj4text of the NGO projections in the spatial_ref_sys
to the correct values, the result is consistent with proj.4
cs2cs.
I have also checked with an independent tranformation
service (Norwegian Mapping Authority), and it gives about
the same results.

As soon as the epsg-file bug of proj.4 has been fixed,
PostGIS users with NGO1948 data should be happy.

Sorry about the noice...

Havard Tveite wrote:
> An important omission in my earlier emails (sorry...):
> The proj.4 epsg +lon_0 parameters (longitude offset) for the NGO
> projections have been strange for the last couple of proj.4
> releases. This has been reported as a bug in proj.4 bugzilla.
> I have fixed the proj.4 epgs parameter file by hand to overcome
> the problems.
> 
> I guess that the PostGIS spatial_ref_sys table is not
> generated from the local proj.4 epsg file...
> The longitude offset probably stems from this.
> 
> The epsg parameter file changes seems to have been made some
> time after proj-4.4.7 (I think this version had correct values
> for both latitude offset and towgs84).
> Where the epsg "errors" come from, I don't know. It could be
> an error introduced when generating the proj.4 epsg file, or
> it could be an error in the EPSG sources. The fact that "NGO 1948"
> and "NGO 1948 (Oslo)" use different prime meridians (Greenwich
> and Oslo respectively) might be one of the sources of confusion.
> 
> I can still not explain the datum shift problems (or what
> ever problem it might be).
> 
> Here are my local values for PostGIS 0.8 and 1.1:
> 
> select * from spatial_ref_sys where srid = 27393;
> 
> 741, postgis 0.8:
>  > 27393 | EPSG      |     27393 | 
> PROJCS["NGO_1948_Oslo_Norway_Zone_3",GEOGCS["GCS_NGO_1948_Oslo",DATUM["D_NGO_1948",SPHEROID["Bessel_Modified",6377492.018,299.1528128]],PRIMEM["Oslo",10.72291666666667],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",0],PARAMETER["Scale_Factor",1],PARAMETER["Latitude_Of_Origin",58],UNIT["Meter",1]] 
> | +proj=tmerc +lat_0=58 +lon_0=10.72291666666667 +k=1.000000 +x_0=0 
> +y_0=0 +a=6377492.018 +b=6356173.508712696 +pm=10.72291666666667 +units=m
> 
> 82 cvs, postgis cvs:
>  > 27393 | EPSG      |     27393 | PROJCS["NGO 1948 (Oslo) / NGO zone 
> III",GEOGCS["NGO 1948 (Oslo)",DATUM["NGO_1948_Oslo",SPHEROID["Bessel 
> Modified",6377492.018,299.1528128,AUTHORITY["EPSG","7005"]],TOWGS84[278.3,93,474.5,7.889,0.05,-6.61,6.21],AUTHORITY["EPSG","6817"]],PRIMEM["Oslo",10.72291666666667,AUTHORITY["EPSG","8913"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4817"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",58],PARAMETER["central_meridian",0],PARAMETER["scale_factor",1],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","27393"]] 
> | +proj=tmerc +lat_0=58 +lon_0=-10.72291666666667 +k=1.000000 +x_0=0 
> +y_0=0 +a=6377492.018 +b=6356173.508712696 
> +towgs84=278.3,93,474.5,7.889,0.05,-6.61,6.21 +pm=oslo +units=m +no_defs
> 
> My share/proj/epsg (assuming that +lon_0 is supposed to give
> the offset from +pm):
> # NGO 1948 (Oslo) / NGO zone III
> <27393> +proj=tmerc +lat_0=58 +lon_0=0 +k=1.000000 +x_0=0 +y_0=0 
> +a=6377492.018 +b=6356173.508712696 
> +towgs84=278.3,93,474.5,7.889,0.05,-6.61,6.21 +pm=oslo +units=m 
> +no_defs  <>
> 
> Michael Fuhr suggested to run cs2cs. With the correct lon_0
> (0 for NGO 1984 zone 3), the results are:
> echo 2836.394208896 185526.991186176 |
> cs2cs +proj=tmerc +lat_0=58 +lon_0=0 \
>       +k=1.000000 +x_0=0 +y_0=0 +a=6377492.018 +b=6356173.508712696 \
>       +towgs84=278.3,93,474.5,7.889,0.05,-6.61,6.21 \
>       +pm=oslo \
>       +units=m +no_defs \
>       +to \
>       +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs \
>       -f "%.8f"
>  > 10.76845023     59.66650218 0.30776738
> 
> Which still seems to be quite far (a few hundred meters) off.
> 
> Very strange that my UMN Mapserver (4.6.1) seems to perform a much
> better transformation (within a couple of meteres)... (I have
> checked visually how the NGO 1948 zone 3 dataset lines up with
> datasets with other coordinate systems when transformed to WGS84
> longlat).
> 
> Perhaps I will have to do some more homework before pursuing this
> further...
> 
> Thank you for your efforts!
> 
> 
> Haavard
> 
> Frank Warmerdam wrote:
> 
>> On 12/22/05, Havard Tveite <havard.tveite at umb.no> wrote:
>>
>>> It is nice to provide warnings, but for epsg:27393 -> epsg:4326
>>> the following problems persist:
>>>
>>> 1) Longitude of origin (+lon_0=-10.72291666666667) is ignored
>>>    (as demonstrated by strk's query).
>>
>>
>>
>> Havard,
>>
>> Are you sure that the the +lon_0 is being ignored?  It seems more
>> likely that it is being undone by the +pm=oslo.  There are a variety of
>> problems with prime meridian handling in the EPSG->proj.4 translation
>> process.  I would suggest modifying the PROJ.4 definition to not
>> include the +pm=oslo and see if that helps.
>>
>>
>>> 2) No datum shift seems to be performed.
>>>
>>> Since the transformation runs smoothly using UMN Mapserver (
>>> with dynamically linked proj - so it should be 4.4.9), there
>>> is probably a problem somewhere.
>>
>>
>>
>> You are likely right, I'm not sure what the story is.
>>
>> Best regards,
>> -- 
>> ---------------------------------------+-------------------------------------- 
>>
>> I set the clouds in motion - turn up   | Frank Warmerdam, 
>> warmerdam at pobox.com
>> light and sound - activate the windows | http://pobox.com/~warmerdam
>> and watch the world go round - Rush    | Geospatial Programmer for Rent
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>>
> 

-- 
Håvard Tveite
Department of Mathematical Sciences and Technology, UMB
Drøbakveien 14, POBox 5003, N-1432 Ås, NORWAY
Phone: +47 64965483 Fax: +47 64965401 http://www.umb.no/imt