Dear Glynn Clements<div><br></div><div>Is there a command r.grow.distance on GRASS?</div><div>I tryed to find it on Native WinGrass, but it appears not be available, almost on 6.3 version.</div><div><br></div><div>Best wishes</div>
<div><br></div><div>miltinho<br><br><div class="gmail_quote">2009/2/14 Glynn Clements <span dir="ltr"><<a href="mailto:glynn@gclements.plus.com">glynn@gclements.plus.com</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="Ih2E3d"><br>
Jan Hartmann wrote:<br>
<br>
> With that in mind, if the algorithm you propose would be indeed an<br>
> approximation to weighted Voronoi polygons, *and* it wouldn't be all to<br>
> hard to implement (I have no idea about that), would it make sense to<br>
> propose this as a new RFC for GRASS?<br>
<br>
</div>Oops; I spoke too soon.<br>
<br>
In retrospect, this won't work. r.grow.distance relies upon the fact<br>
that once a cell falls out of consideration, it stays out. It will<br>
only consider cells which either are from the current row, or were<br>
used on the previous row.<br>
<br>
With distance scaling, this doesn't hold. A cell could be temporarily<br>
overriden by much nearer cells with increased scale factors (lower<br>
weights), then regain its influence once the distance increases.<br>
<br>
IOW, this isn't something which can implemented given the algorithm<br>
used by r.grow.distance. Any algorithm which implemented distance<br>
scaling would inevitably have worst-case memory usage proportional to<br>
the number of non-null input cells, as you can never "forget" a cell<br>
whose scale factor is lower than those currently being considered, as<br>
it will eventually regain its influence.<br>
<div><div></div><div class="Wj3C7c"><br>
--<br>
Glynn Clements <<a href="mailto:glynn@gclements.plus.com">glynn@gclements.plus.com</a>><br>
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</div></div></blockquote></div><br></div>