[GRASS-user] Projection Units and Values Negatively Affect r.topidx Results

[Rich Shepard]

On Tue, 16 Feb 2010, Rich Shepard wrote:

>  I discovered what I believe is a problem with the projection units on my
> source DEM. They're in International Feet so the projection listing shows
> 32.81948362. That's the feet equivalent of 10m. What I'd like to learn is
> how to change that value to 10.0 to match the PROJ_UNITS in meters.

   Here's what r.info reports for the source and resampled DEMs:

Source:

  |---------------------------------------------------------------------------|
  |   Type of Map:  raster               Number of Categories: 5729	     |
  |   Data Type:    CELL							     |
  |   Data Units:   meters               Vertical datum: feet	             |
  |   Rows:         1684							     |
  |   Columns:      1525							     |
  |   Total Cells:  2568100						     |
  |        Projection: Lambert Conformal Conic				     |
  |            N: 1334419.25160578    S: 1279151.24118496   Res: 32.81948362  |
  |            E: 819255.92362222    W: 769192.9282895   Res: 32.82819366     |
  |   Range of data:    min = 7  max = 1473				     |
  |									     |
  |   Data Description:							     |
  |    generated by r.in.gdal						     |
  |   Comments:								     |
  |    r.in.gdal input="/usr4/dem10m-or/hdr.adf" output="dem" title="Northw\  |
  |    est Oregon 10m DEM"						     |

   Note that the _horizontal_ data units are meters but the resolution is
32.81948362 which is approximately the English (feet) equivalent of 10
meters. So, when I resample this map to 5 meters resolution r.info reports:

  |   Type of Map:  raster               Number of Categories: 255	     |
  |   Data Type:    DCELL						     |
  |   Rows:         11054						     |
  |   Columns:      10013						     |
  |   Total Cells:  110683702						     |
  |        Projection: Lambert Conformal Conic				     |
  |            N: 1334419.25160578    S: 1279151.24118496   Res: 4.99982001   |
  |            E: 819255.92362222    W: 769192.9282895   Res: 4.99979979      |
  |   Range of data:    min = 7.000000  max = 1472.900398		     |
  |   Data Source:							     |
  |    aberDEM								     |
  |    Source map NS res: 32.81948362   EW res: 32.82819366		     |
  |   Data Description:							     |
  |    generated by r.resamp.interp					     |
  |   Comments:								     |
  |    r.resamp.interp input="aberDEM" output="aber5m" method="bilinear"      |

   In the latter I see the 'res' as approximately 5 meters based on a source
map resolution of approximately 10 meters expressed in feet.

   My questions are:

   1) how do I change the source map's resoluttion to 10 meters to match the
units?

   2) Do I need to recreate the resampled, 5 meter resolution map after doing
#1?

Thanks,

Rich