[GRASSLIST:7760] RE: cross validation on v.srf.rst. Does it work?

[Jaime Carrera]

Hi Tom

But I think that the values I get from running
v.srf.rst and the difference between the interpolated
map and the real value should be the same no matter
what value I use for smoothing. Am I right?

Jaime

 --- Tom Colson <tom_colson at ncsu.edu> escribió:

> Just for grins..try smooth=.01 or .02. My first
> suspicion would be that
> there is too much smoothing. How many points are in
> the rainfall data
> set...and what is the average distance between
> points? 
> 
> 
> Thomas Colson
> North Carolina State University
> Department of Forestry and Environmental Resources
> (919) 673 8023
> tom_colson at ncsu.edu
> 
> Calendar:
> www4.ncsu.edu/~tpcolson
>  
> 
> -----Original Message-----
> From: owner-GRASSLIST at baylor.edu
> [mailto:owner-GRASSLIST at baylor.edu] On
> Behalf Of Jaime Carrera
> Sent: Tuesday, August 02, 2005 8:57 AM
> To: grasslist at baylor.edu
> Subject: [GRASSLIST:7758] cross validation on
> v.srf.rst. Does it work?
> 
> Hi all,
> 
> I'm trying to use the cross validation option on
> both v.srf.rst and
> v.vol.rst. However I'm getting some strange results
> for the slovakia
> rainfall data set. 
> 1) I ran v.srf.rst as follows: 
> GRASS 6.0.0 (slovakia3d):~ > v.surf.rst input=rain3d
> zcolumn=int_1 cvdev=cv1 -v mask=mask at PERMANENT
> 
> Which wrote a table with difference values on
> Postgres.
> 
> 2) Then I created another table without the gauging
> station #122 (which I
> called rain3d_2) and interpolated using the same
> parameters as above:
> GRASS 6.0.0 (slovakia3d):~ > v.surf.rst
> input=rain3d_2 zcolumn=rain
> mask=mask at PERMANENT elev=vsurf1_wo122
> 
> AFAIK cross validation removes one point at a time,
> interpolates using the
> remainder points and computes the difference between
> the interpolated value
> at a certain location (i.e. station 122) and the
> real value (record at
> station 122).  Accordingly if I query the raster map
> vsurf1_wo122 at the
> coordinates of station
> 122 and substract the interpolated value to the real
> value I should get the
> value that was written to the cross validation table
> for station 122, so I
> query the
> map:
> GRASS 6.0.0 (slovakia3d):~ > r.what
> input=vsurf1_wo122
> east_north=4416904,5414029
> 4416904|5414029||1057.9642333984
> 
> The real value at station 122 is 798 mm; according
> to these values the
> difference is: 1057.96-798 = 259.96.
> The value that was written by the v.srf.rst module
> on the cross-validation
> table is -5.31.
> 
> Can someone tell me what's going on here?
> 
> Cheers,
> 
> Jaime
> 
> 
> 
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> 


__________________________________________________
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Espacio para todos tus mensajes, antivirus y antispam ¡gratis! 
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