[Qgis-user] qgis random points in layer bounds not all points created

[Newcomb, Doug]

Newcomb, Doug wrote
>>* I have 81 points that I buffer by 25m. I then run the random points in
*>>* layer bounds tool to generate 100 points. I get 43 and a message that not
*>>* all points were created.
*>>* I ask for 300 points, and I get 160 .
*
>The algorithm tries to randomly place each point for up to 200 attempts. So,
>more points to be created, more attempts.

>Obviously, did you specify the same minimum distance value in both your test
>for 100 and 300 points?

>The chance to place the whole number of requested points depends on the
>geometric characteristics of the polygons ad how are distributed in the
>space and the constraint of the minimum distance between each point. If this
>value is too large (e.g. in your case, > 50 m) then the problem may have no
>solution.

>By the way, it seems to me that the description of the algorithm in the user
>manual is not accurate and should be improved.
>It states that the tool creates random points within the _extent_ of a given
>layer, but it is not so.

>Regards.

>Andrea

Andrea,

Thank you.  Double checking the minimum distance got me on the right track.

One thing to note. I used the buffer layer to clip a soil polygon
layer that was multipart. The clipped layer needed to be converted to
single part to place a single point in each polygon derived from the
buffered layer clip.

Are there any plans to make the number of tries to be a user
accessible variable in the GUI?


Doug



-- 
Doug Newcomb - Cartographer
USFWS
551F Pylon Dr
Raleigh, NC
919-856-4520 ext. 14 doug_newcomb at fws.gov
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