# [OSRS-PROJ] Oblique Mercator, and Swiss Oblique Cylindrical

Clifford J Mugnier cjmce at lsu.edu
Wed Dec 11 17:18:22 EST 2002

```Frank,

Try:

Latitude = 48º 44' 35.8774" N
Longitude = 8º 47' 55.1112" E
X = Northing = 400000.000
Y = Easting = 700000.000
Convergence Angle = +0º 59' 37.5"
Scale Factor = 1.0004915

Latitude = 48º 00' 00.0000" N
Longitude = 9º 00' 00.0000" E
X = Northing = 317623.181
Y = Easting = 716458.038
Convergence Angle = +1º 08' 26.1"
Scale Factor = 1.0001700

Latitude = 48º 00' 00.0000" N
Longitude = 8º 00' 00.0000" E
X = Northing = 316613.532
Y = Easting = 641836.510
Convergence Angle = +0º 24' 35.0"
Scale Factor = 1.0001671

However, the Swiss Office of Topography DOES have a web site, and when I
checked a few years ago, they had TWO papers on their Datum and their
Rossenmund projection in English in ".pdf" format.  I don't have the files
with me at the moment, but you should be able to get them easily.

I published my column on the Grids and Datums of the Swiss Confederation in
"Photogrammetric Engineering and Remote Sensing" in August, 2001, pp.

Note that the Swiss, Hotine, and Laborde (Madagascar) implementations are
each different from each other.

Regards,

Cliff Mugnier
LOUISIANA STATE UNIVERSITY

------------------------------------------

Folks,

I am working on getting Swiss Oblique Cylindrical working properly in a
higher level tool build on PROJ.4, and am running into a number of
problems.

1) The omerc projection in PROJ.4 does not let me select an azimuth of 90
degrees.  My understanding is that Swiss Oblique Cylindrical is
essentially
Oblique Mercator with an azimuth of 90 but that is clearly considered a
degenerate case in the PJ_omerc code (and it reports an error).  Is
this
just due to the mathematical formulation of the omerc code?

2) I have tried setting the azimuth quite close to 90 (ie. 89.99) and
PROJ.4 seems to work but the results do not match what I am expecting.
Off by a few thousand meters in my test case.  My test point was
derived
by using FME to reproject some swiss data into lat/long on the same
datum.
Does anyone have a sample point I could use in swiss oblique
cylindrical?
That is, the location in lat/long and soc?

3) Just to ensure I had a known starting point, I tried reprojecting the
example point from the EPSG note on oblique mercator.  This is
described
in section 1.4.7 of their "Guidance Note # 7".  The section is
available at:

http://www.remotesensing.org/geotiff/proj_list/epsg_om.html

However, I could get my results to agree.  Basically I tried:

proj +proj=omerc +lat_0=4 +lonc=115 +alpha=53.31582047222222
+k=0.99984
+x_0=590476.87 +y_0=442857.65 +ellps=evrstSS +units=m < rso_eg.dat

where rso_eg.dat contains:

115d48'19.8196"E 5d23'14.1129"N
# 679245.73 596562.78 expected

But instead of getting the expected results I get:
679743.48       596274.24

It is in the right ballpark, but still on the order of 600 meters off.
Can anyone suggest where things are going wrong?

Actually, looking over things, there doesn't seem to be a
"rectified to skewed grid" argument in my proj.4 formulation.  Is that
an issue?  I don't really follow the purpose of this parameter as
opposed
to the azimuth.

Best regards,

--
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I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent

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```