[GRASSLIST:5787] Re: GRASS Novice Needs Help

[Ian MacMillan]

John,
I think your problem is that your Irish grid is in transverse mercator, 
which means the units of measurement is meters, not degrees.  Typically 
your coordinates will be measured in several hundred thousand to 
millions of meters.  Latlong locations measure everything in degrees 
(like you have).  Somehow, you will need to get the correct coordinates 
in meters for your irish grid first, and then r.proj into your latlong 
grid.  Or mebbe you can try to just go straight into your latlong grid? 
  Not sure if this is super helpful but mebbe this can help get you 
started.

G'luck
-Ian

On Feb 15, 2005, at 2:48 AM, John Ronan wrote:

> Morning,
>
>
> I recently came across Grass when I posted on another list asking the 
> question on how to convert scanned images into georeferenced images 
> that could be used in xastir (www.xastir.org). So in fact Im not quite 
> knowledgeable enough to call myself a novice even.
>
> Thus far I've managed to convert the tiffs to unprojected lat/long 
> rasters that xastir (www.xastir.org) can use and in fairness they seem 
> to be pretty accurate.  This was only possible by the extra-ordinary 
> patience of Gerry Creager and Tom Russo. Who pretty much walked me 
> through it step by step, thanks guys.
>
> Anyways my problem now is trying to get rid of the 'fluff' that gets 
> created around the edges by gdalwarp when it does the 'warping'. I've 
> been attempting to use r.patch followed by r.proj to reproject the 
> patched raster into another lat/long database but I've thus far not 
> been successful.
>
> I'm currently getting the error 'Input map is outside current region', 
>  here are the regions,
>
>
> Firstly the Irish Grid.
> projection: 99 (Transverse Mercator)
> zone:       0
> datum:      ire65
> ellipsoid:  modif_airy
> north:      52.3
> south:      52.15
> west:       -7.4
> east:       -6.85
> nsres:      0.15
> ewres:      0.55
> rows:       1
> cols:       1
>
> The Lat/Long region (bigger than the one above I think)
> g.region -p
> projection: 3 (Latitude-Longitude)
> zone:       0
> datum:      wgs84
> ellipsoid:  wgs84
> north:      54N
> south:      52N
> west:       9W
> east:       5W
> nsres:      0:00:00.187198
> ewres:      0:00:00.1872
> rows:       38462
> cols:       76923
>
> So I've done a r.patch of two 'tiles' in the Irish Grid Database 
> called ubermap. I exit grass, open it in the 'latlong' location and 
> try to do r.proj
>
> r.proj input=ubermap location=Ireland mapset=osmaps output=waterford1 
> method=nearest
>
> Input Projection Parameters: +proj=tmerc +lat_0=53.5000000000 
> +lon_0=-8.0000000000 +k_0=1.0000350000 +x_0=200000.0000000000 
> +y_0=250000.0000000000 +a=6377340.189 +rf=299.3249646 +no_defs 
> +towgs84=482.530,-130.596,564.557,-1.042,-0.214,-0.631,8.15
> Input Unit Factor: 1
>
> Output Projection Parameters: +proj=latlong +a=6378137 
> +rf=298.257223563 +no_defs +towgs84=0.000,0.000,0.000
> Output Unit Factor: 1
> ERROR: Input map is outside current region
>
> And I'm stuck... as I've really got no idea what I'm doing here any 
> help would be appreciated.
>
> Regards
> de John
> EI7IG
>