[GRASSLIST:5699] Re: r.in.gdal problem?

[Glynn Clements]

David Orme wrote:

> I'm using the r.in.gdal module to import ARCINFO GRID format raster  
> files and I seem to be getting a shift in the extent of the data on  
> import:
> 
> The files contain 1 by 1 degree resolution raster data. In Arc, the NS  
> extent of the raster data is:
> 
> bottom edge of southernmost grid square = 90S
> topmost edge of northernmost square = 77N
> 
> The raster therefore contains 167 rows of data.
> 
> When I import this, the file extent is as follows:

> >  |        Projection: UTM (zone 13)                                             |
> >  |            N:       77.5    S:      -89.5   Res:     1                       |
> >  |            E:      330.5    W:     -226.5   Res:     1                       |

> The number of rows (and columns) are correct but the extent is peculiar  
> - I'm guessing that r.info returns the centre points of the grid cells  
> but if this is the case then the centre of the northernmost cell should  
> be at 76.5N not 77.5N.  This also makes the reported southern extent  
> odd since the 89.5 S implies that there is still a gridsquare that has  
> 90S as a bottom edge. Using d.where to inspect the location visually  
> shows that the top of the northernmost cell in grass is now at 78N and  
> the bottom of the lowermost cell is at 89S.
> 
> Something doesn't add up - I'm expecting to find that it may be me but  
> can anyone clear this up?

The GRASS region refers to cell corners, not centres; it seems that
r.in.gdal is misinterpreting the region information in the grid file.

You can fix the resulting map manually using r.region, e.g.

	r.region map=... n=77 s=-90 ...

However, you appear to have imported the data into a UTM location,
when the data is actually lat/lon.

-- 
Glynn Clements <glynn.clements at virgin.net>