[GRASS-dev] Re: v.generalize and interpolation, dmax problem

[Helena Mitasova]

On Aug 17, 2007, at 5:21 AM, Paul Kelly wrote:

> On Fri, 17 Aug 2007, Helena Mitasova wrote:
>
> [Interesting/impressive test results...]
>
>> which brings me to the main question - are there any objections to  
>> make dmax default value
>> as large as the region to make sure that it does not add any points
>> (currently it is set to 1.25 resolution value which is obviously  
>> not enough)?
>> I have been trying to eliminate this parameter for years
>> as it usually causes more problems than it solves.
>
> For 7.x perhaps you could drop both the dmin and dmax parameters,  
> and add a note to the man page suggesting that the user preprocess  
> their contour data with v.generalize to resolve issues with closely- 
> spaced points, before running v.surf.rst?

I will eliminate dmax in GRASS7 (if I still remember it) but dmin  
needs to stay.
v.generalize applies only to lines or area boundaries
so the preprocessing can be used only for contours -
dmax applies only to contours (it does the same thing as v.to.point - 
vi )
- it does nothing if your input are scattered points.
We still need dmin for preprocessing of scattered points and for  
elimination of points
that may be too close to each other due to density of contours on  
steep slopes.

Profiles that you may get from real time kinematic survey or single  
beam sonar
have similar problem as contours with points being much denser along  
the profile compared
to the distance between profiles, but they would require  
generalization in vertical plane rather
than the horizontal plane.

v.generalize should also help with v.surf.idw and kriging in case  
somebody wants to use
those methods to grid from contours or isolines.

Helena




>
> Just a thought
>
> Paul