Jan Quets <jan.qu...@ua.ac.be> writes: > 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
If the 'predetermined set of marks' is a finite set of radii, then this is a special case of the multitype Strauss process, where you set the interaction distance between mark r1 and mark r2 to be r1+r2, and the interaction parameters gamma are all equal to zero. Suppose 'rvals' is a vector containing the desired radii, 'W' is the simulation window and 'b' is the base intensity. Then do m <- length(rvals) types <- 1:m rmat <- outer(rvals, rvals, "+") gmat <- matrix(0, m, m) mod <- rmhmodel(cif="straussm", par=list(beta=rep(b, m), gamma=gmat, radii=rmat), w=W) This defines the model. Then if you want simulations of exactly k points, sta <- rmhstart(n.start=k) con <- rmhcontrol(p=1) If you now call X <- rmh(mod, sta, con) you'll get a multitype point pattern with marks 1:m where mark j corresponds to radius rvals[j]. If you need to convert this to a marked point pattern with the radii as the marks, do something like marks(X) <- rvals[marks(X)] To use this in envelope(), set mapmarks <- function(X, v=rvals) { marks(X) <- v[marks(X)]; return(X) } expr <- expression(mapmarks(rmh(mod, sta, con))) then call envelope(....... simulate=expr) If the 'predetermined set of marks' is a continuous range of radii, then there does exist some code to do this, but it is not yet released in spatstat. Adrian Baddeley _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo