[GRASS-dev] v.surf.bspline density and distance estimates

[Paulo van Breugel]

On 6/16/17 3:20 PM, Markus Metz wrote:
>
>
> On Fri, Jun 16, 2017 at 11:28 AM, Paulo van Breugel 
> <p.vanbreugel at gmail.com <mailto:p.vanbreugel at gmail.com>> wrote:
> >
> > Hi devs, can anybody tell how v.surf.bspline computes the point 
> density and mean distance.
>
> point density is the number of points divided by the size of the 
> bounding box of the points
> mean distance is the square root of the size of the bounding box 
> divided by the number of points
>
> > And what is the unit, pixels, as also used for length spline steps 
> or meters?
>
> the unit is map unit, you can then figure out a reasonable resolution 
> (in map units) for the current region

I think it would be good to add your explanation to the manual page. I 
was trying to come up with a text, but then I realized there is still 
some ambiguity left.

According to the manual page, the ns_step and ew_step parameters are in 
pixels (which I would interpret as 'number of pixels'). However, the 
example of 'Basic interpolation and raster output with a longer spline 
step' in the manual page talks about mapping units.

v.surf.bspline input=point_vector raster=interpolate_surface ew_step=25 
ns_step=25
A bilinear spline interpolation will be done with a spline step length 
of 25 map units.

So if the region's resolution is 100 meter, is the ns_step and ew_step 
2500 meter (25 pixels) or 25 meters? The former would be more conform 
common practice in grass I think.



>
> Markus M
>
> >
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