[GRASS-user] RE: reprojection issue, using grass6.2

[Duffy, Garret]

Hi,

After doing some more investigating, it appears g.proj  is not reading
all the parameters in :

proj=omerc +ellps=WGS84 +k_0=1.0 +lat_0=53.25 +no_uoff +rot_conv
+alpha=-88 +lonc=-5.7

For example, the above command projects (-5.7d, 53.25d) correctly to
(X,Y)=(-5901478, 7901021).  But after g.proj, the same point projects to
(X,Y)=(0,0).

Can someone help with this?

Thanks,

Garret


Dr. Garret Duffy
______________________
Department of Earth and Ocean Sciences

National University of Ireland, Galway
University Road
Galway
IRELAND

Office:  +353 (0)91 492169
Fax:  +353 (0)91 750533



> _____________________________________________ 
> From: 	Duffy, Garret  
> Sent:	12-Oct-11 12:29 PM
> To:	'grass-user at lists.osgeo.org'
> Subject:	reprojection issue, using grass6.2
> 
> Hi,
> 
> I have three locations defined, one in Geographic 'projection', one
> UTM and the other described below.  When I try to reproject data, e.g.
> a vector rectangle from either Geographic or UTM to the Oblique
> Mercator projection defined below, the rectangle isn't rotated as I
> expect.  The origin of the projected coordinates looks to be in the
> correct location but there is no rotation applied (geographic north is
> supposed to ~45 deg from the y axis).  BTW, is it even possible to
> display a geodetic grid for a non-rectified projection?
> 
> output from g.proj -p:
> -PROJ_INFO-------------------------------------------------
> name       : Oblique Mercator
> proj       : omerc
> a          : 6378137
> es         : 0.006694379990141316
> lat_0      : 53.25
> lonc       : -5.7
> alpha      : -88
> k          : 1
> x_0        : 0
> y_0        : 0
> towgs84    : 0,0,0,0,0,0,0
> no_defs    : defined
> -PROJ_UNITS------------------------------------------------
> unit       : meter
> units      : meters
> meters     : 1
> 
> 
> The command I used to specify the oblique projection is:
> 
> proj +proj=omerc +ellps=WGS84 +k_0=1.0 +lat_0=53.25 +no_uoff +rot_conv
> +alpha=-88 +lonc=-5.7
> 
> I must emphasize that I have checked the proj.4 parameters using the
> command-line proj.4 and the *parameters are correct*.  I applied these
> parameters in GlobalMapper to get the final map to the state that I
> would like eventually in GRASS.
> 
> Any advice would be *greatly* appreciated, I have spent a lot of time
> on this.
> 
> Regards,
> 
> Garret
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