[R-sig-Geo] existance of a specific non-overlapping marked spatial model in spatstat or other R package?

[Rolf Turner]

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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