[Proj] Oblique Mercator problem?

Frank Warmerdam warmerdam at pobox.com
Fri Sep 6 18:24:21 EST 2013


We have been through a morass with oblique mercator and it's different
forms over recent years, and I'm afraid I don't recall all the details.
There is some discussion at:


I observe that you get the old results if the +no_rot flag is omitted:

invproj +proj=omerc  +lat_0=33 +lonc=-116 +alpha=45 +ellps=WGS84
0 0
116dW    33dN

I think at least part of the issue had to do with where the +no_rot flag
was interpreted relative to but I'm not inclined to investigate deeply.
Ticket #104 has points to some other tickets that might help.

It might be nice for us to prepare an FAQ entry explaining the changes and
when they came into effect if someone can summarize simply.

Best regards,

On Fri, Sep 6, 2013 at 3:58 PM, Duncan Agnew <agnew at cahuilla.ucsd.edu>wrote:

> Under proj 4.7.1, if I input   0 0    to
> invproj +proj=omerc +no_rot +lat_0=33 +lonc=-116 +alpha=45 +ellps=WGS84
> I get     116dW   33dN   as output. However, doing the same for proj4.8.0
> gives
>         144d29'13.013"W 0d4'39.96"S
> I've been using proj for some time; this has me baffled. (I should note
> that the inverse and forward are consistent in both versions).
> proj 4.7.1 was installed on Mac OSX 10.5, 4.8.0 on MacOSX 10.8
> installed from MacPorts
> Thanks
> Duncan Agnew
> dagnew at ucsd.edu
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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 Software Developer
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