[Proj] apply plane rotation after transverse Mercator projection

Fri Oct 14 02:47:31 PDT 2011

Garret Duffy wrote:

> So this leads to two question and one request:
> 
> Q1) does omerc take the gamma parameter now? I am running v. 4.5

Depends on what you mean by "now". I think the status remains as
it was reported in the thread you linked to.  That is, there is 
no official release that supports omerc with gamma, but the trunk
does, and apparently you can get the proj.4 trunk from OSGeo4W 
(I haven't tried to use gamma in OSGeo4W.)

> Q2) what are the limits of alpha?

Don't know, but I would think that two alpha values that differ 
by 180 degrees give equivalent results. I mean, it should not matter
if you say that the initial line goes southwest or northeast from
the projection center; it is the same line that is specified. 
(I haven't tested this either.)

> R3) Would it be possible to design a new CRS similar to tmerc
>     but taking a gamma parameter?

I have implemented something similar in Carmenta Engine: the
RotatedProjection takes a base projection and modifies it by rotating
the projected plane a specified angle around a specified projected point.
I don't know if something similar would fit in the Proj.4 framework.  
But a gamma parameter could be added to any projection in Proj.4, I believe.  

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

-----Original Message-----
From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of Garret Duffy
Sent: Thursday, October 13, 2011 11:09 AM
To: proj at lists.maptools.org
Subject: Re: [Proj] apply plane rotation after transverse Mercator projection

Yes, I've tried the omerc projection with +rot_conv and +no_uoff but the issue is the alpha azimuth parameter is actually the angle of the rotated cylinder about the ellipsoid (I think the limits are +/- 90?  Can anyone
confirm??) and this angle bears little or no relation to the azimuth of the projected y-axis relative to true north.  I tried making a bunch of projections with different alpha angles and +rot_conv and +no_uoff but is was very hard to precisely control the rotation of the linear features I was interested in measuring.

I think this thread involving Mikael and Frank discusses it well

http://osgeo-org.1803224.n2.nabble.com/looking-for-the-right-params-for-RSO-td5468455.html

It appears that the gamma parameter should actuate an XY_PLANE_ROTATION...

So this leads to two question and one request:

Q1) does omerc take the gamma parameter now? I am running v. 4.5

Q2) what are the limits of alpha?

R3) Would it be possible to design a new CRS similar to tmerc but taking a gamma parameter?

Thanks everyone for your advice.

Garret
"Mikael Rittri" <Mikael.Rittri at carmenta.com> wrote in message news:11AC4CEB-F5B7-45A1-BE18-730A3FABD1C2 at carmenta.com...
The Rosenmund projection is called +proj=somerc (Swiss Oblique Mercator), but I don't see why that should be better than the RSO (+proj=omerc) for this purpose.

I don't think there is any built-in support in Proj.4 to do an arbitrary rotation of the projected plane.
However, if you just need to rotate 90, 180 or 270 degrees, then you could perhaps use the +axis parameter.

Best regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

Den 12 okt 2011 kl. 15:53 skrev "Clifford J Mugnier" <cjmce at lsu.edu>:

I don't know if PROJ4 has it, but the Rosenmund projection as used in Switzerland sounds like what you want.

Clifford J. Mugnier, C.P., C.M.S.
Chief of Geodesy,
Center for GeoInformatics
Department of Civil Engineering
Patrick F. Taylor Hall 3531
LOUISIANA STATE UNIVERSITY
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic] Voice and Facsimile:  (225) 578-4578 [Research]
Cell: (225) 328-8975 [Academic & Research] Honorary Life Member of the Louisiana Society of Professional Surveyors Fellow Emeritus of the ASPRS Member of the Americas Petroleum Survey Group

From: proj-bounces at lists.maptools.org on behalf of Duffy, Garret
Sent: Wed 12-Oct-11 06:13
To: proj at lists.maptools.org
Subject: [Proj] apply plane rotation after transverse Mercator projection

Hi,
I would like to design a projection that is similar to a TM projection except append the parameter "XY_Plane_Rotation", i.e. rotate the XY axes.
Is this possible to do in PROJ4?  I note the tmerc doesn't have an alpha parameter or similar.  I already tried using RSO but it's overkill for what I want to do, all I want to do is apply a simple cartesian rotation to the projected XY axes.
Another thing I tried was editing a PRJ file for a TM projected data and then appending "PARAMETER["XY_Plane_Rotation",XX]" to the file but that doesn't seem to work.
Do I have to define a custom PROJCS that is based on tmerc but allows for the XY_Plane_Rotation parameter?
Any suggestions gratefully would be (very) gratefully received as I have been trying to do this supposedly simple thing all week.
Regards,
Garret
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