[GRASSLIST:9462] Re: V.sample - what does the column parameter refer to?

[Markus Neteler]

Eric,

it's an existing column.
I have updated description in CVS and added this example
(I hope I got it right):

Comparison of "elevation.dem" and "elevation.10m" Spearfish maps
at random places:

#generate random points:
 v.random output=random n=100
#add table with one column:
 v.db.addtable random col="el10 double"
#transfer elevations at random points into table:
 v.what.rast rast=elevation.10m vect=random col=el10
#verify:
 v.db.select random

#generate sampling from other elevation map:
 v.sample in=random col=el10 rast=elevation.dem out=elev_sample

#verify:
 v.db.select elev_sample

#univariate statistics of differences between elevation maps:
 v.univar elev_sample col=diff

cheers

 Markus
On Fri, Dec 09, 2005 at 11:29:27AM -0400, Patton, Eric wrote:
> Is the column parameter of v.sample referring to an empty column in the
> vector attribute file, or - a new column that will be created during the
> sampling of the raster, or - an existing column?
> 
> I've tried sampling a raster using an empty column I created using
> v.db.addcol (type was DOUBLE), and I got nothing but zeros populated in the
> column in question. Region was good, it was set to that of the sampling
> vector. 
> 
> ~ Eric.
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  
> Eric Patton
>  
> Technologist, Geo-Spatial Data Services
> Geological Survey of Canada (Atlantic)
> Natural Resources Canada
> Bedford Institute of Oceanography
> Dartmouth, Nova Scotia, Canada B2Y 4A2
>  
> Postal address: P.O. Box 1006
> Courier address: 1 Challenger Drive
>  
> Telephone: (902)426-7732
> Facsimile:  (902)426-4104
> E-mail:       epatton at NRCan.gc.ca
>  
> 

-- 
Markus Neteler     <neteler itc it>       http://mpa.itc.it
ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
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