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<div class="moz-cite-prefix">On 6/25/17 11:09 PM, Markus Metz wrote:<br>
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cite="mid:CAG+h=FHNyk9iU5JHfw7S85b0O=LAtiW5hfRGA1SE7z3wL0pOKQ@mail.gmail.com">
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On Sat, Jun 24, 2017 at 11:23 AM, Paulo van Breugel <<a
href="mailto:p.vanbreugel@gmail.com"
moz-do-not-send="true">p.vanbreugel@gmail.com</a>>
wrote:<br>
><br>
><br>
> On 6/16/17 3:20 PM, Markus Metz wrote:<br>
><br>
><br>
><br>
> On Fri, Jun 16, 2017 at 11:28 AM, Paulo van Breugel
<<a href="mailto:p.vanbreugel@gmail.com"
moz-do-not-send="true">p.vanbreugel@gmail.com</a>>
wrote:<br>
> ><br>
> > Hi devs, can anybody tell how v.surf.bspline
computes the point density and mean distance.<br>
><br>
> point density is the number of points divided by the
size of the bounding box of the points<br>
> mean distance is the square root of the size of the
bounding box divided by the number of points<br>
><br>
> > And what is the unit, pixels, as also used for
length spline steps or meters?<br>
><br>
> the unit is map unit, you can then figure out a
reasonable resolution (in map units) for the current region<br>
><br>
><br>
> 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.<br>
><br>
> 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.<br>
><br>
> v.surf.bspline input=point_vector
raster=interpolate_surface ew_step=25 ns_step=25<br>
> A bilinear spline interpolation will be done with a
spline step length of 25 map units.<br>
><br>
> 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.<br>
<br>
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The unit of ns_step and ew_step is map units, but that does
not really make sense, the unit of the spline steps should
rather be pixels. However, the unit of the spline step options
can not be changed because it would break compatibility.<br>
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<br>
In the manual page, in the first paragraph of the Notes, may I
suggest to change the text:<br>
<p>The length of each spline step
is defined by <b>ew_step</b> for the east-west direction and
<b>ns_step</b> for the north-south direction. Step is defined in
number of pixels. </p>
<p>to something along the lines:<br>
</p>
The length (in mapping units) of each spline step
is defined by <b>ew_step</b> for the east-west direction and
<b>ns_step</b> for the north-south direction.<br>
<br>
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Markus M<br>
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