[OSRS-PROJ] Converting from WGS-84 to Sweden's RT-90

[Clifford J Mugnier]

Complaining about 10-15 cm is NOT a cartographic problem.

At that level of precision, you are talking geodesy.

PROJ4 is not designed or intended for geodetic results with a 7-parameter
transformation for a national solution.

The Kingdom of Sweden has a series of software packages for their country
that yields excellent geodetic results.  I suggest that you use their very
special software for high accuracy results if that's what you need.  A
7-parameter datum shift (either the Bursa-Wolf or the Molodensky models)
will yield decimeter results for a area about the size of a United States
county, certainly NOT the entire country of Sweden.

PROJ4 is for cartographers doing cartography and remote sensing with GIS
tools.

Cliff Mugnier
LOUISIANA STATE UNIVERSITY
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On Mon, 9 Feb 2004, Alexander Isacson wrote:

> Hello list.
>
> I'm looking for a way to transform coordinates (WGS-84 lat, long) from a
> GPS receiver to RT-90 (N/E) which is local grid here in Sweden. I'm
> really new to all this and I'm just realizing that these transformations
> are allot harder than I thought. Hopefully PROJ.4 can help me out.
>
> To go form WGS-84 to RT-90 one has to preform the seven-parameter
> translation. http://www.geocities.com/mapref/prj/se/se.html
>
> How do I preform this transformation? Can it be done with cs2cs? Is
> there a +fromwgs84 parameter?

I found a 7-parameter transformation at this website:
http://crs.ifag.de/country_select.php?country=SE

The following command line gives OK results but they are some 10-15cm out
from the test point at
http://www.geocities.com/mapref/prj/se/se_rt90simp.html and I don't know
what's causing that. You should maybe try with some other software to
verify proj.4's result. The problem may simply be the small error
resulting from treating SWEREF93 and WGS84 as the same thing (they are
close enough for many purposes).

echo 18d7\'29.50084\" 66d19\'4.85672\" | \
cs2cs +proj=longlat +datum=WGS84 +to +proj=tmerc +lat_0=0 \
+lon_0=15d48\'29.8\" +x_0=1500000 +k_0=1 +ellps=bessel \
+towgs84=414.1,41.3,603.1,-0.855,2.141,-7.023,0
1604007.49      7359600.91 -31.26

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