On 28/05/2010, at 8:53 AM, Quets Jan wrote:
>
> Hi,
>
> I am looking for a specific non-overlapping marked spatial model for use as a
> null model for monte carle simulations with use of the 'envelope' function in
> spatstat.
>
> the specific marked spatial model should:
> -----------------
> *generate a spatial random pattern with a predetermined number of points
> (with conditions set below)
>
> *each point should be assigned a mark randomly out of a predetermined set of
> marks
>
> *these marks represent the radia of circular discs which should be drawn
> around these points (which act as centres)
>
> *no discs should overlap
> -----------------
>
> Does anybody has knowledge of a such a built in model in spatstat or another
> R package?
>
> For now, I have built this model by myself, but it turns out to have a very
> time-consuming running time, especially when used as a null model in a monte
> carlo simulation. Also I have multiple monte carlo simulations to perform.
>
> It will be of great help,
The only way I can think of doing this is sequentially. I.e. select a radius,
then repetitively select a point to add, rejecting the selected point if its
circle (with the chosen radius) intersects any of the existing circles. If
after ``giveup'' attempts the function has failed to find an acceptable point,
it gives up (and throws an error).
I cobbled together some code to effect this; it took one minute of user time
to do 100 replications of choosing 100 points with non-overlapping circles
in the unit square, with the radii selected uniform-randomly from (1:5)/100
and giveup=1000.
I believe that it would require a lot of work and great cleverness to get
anything substantially faster. Of course, I could be wrong --- I was once,
back in 1968 when I thought I'd made a mistake and I hadn't. :-)
cheers,
Rolf Turner
P. S. Let me know if you want my code. I suspect it's not much different
from what you have built yourself.
R.
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