Hi Roman,

you don't say which is the format of your roads covariate but, if you 
are able to convert it to a linnet or  psp object, you have several 
easy options to compute images. For example:

data(simplenet)
plot(simplenet)

plot(pixellate(as.psp(simplenet)))

plot(distmap(as.psp(simplenet)))


By the way, instead of a quadrature  scheme you could also use  rsyst 
to generate directly a grided ppp with "real" observations and then 
mark the points  at will.

HTH
MArcelino


At 13:33 04/05/2011, Roman Hornung wrote:
>Hello everyone,My data consists of marked points and several 
>covariates, whereby the marks are the time points of the 
>observations. The problem is, that one of the covariates is hard to 
>handle as an image. This covariate represents the type of roads. As 
>there aren't roads at every location of the map, one cannot specify 
>the value of the covariate at any point on a grid, which is 
>necessary to specify an image. To tackle this, I wanted to use a 
>quadrature scheme and use points on the roads as dummy points 
>instead of a data point pattern as the outcome variable. The problem 
>I now encounter is, that I can't give marks to the dummy points, 
>since they are no "real" observations (and omitting the marks gives 
>an error).Does somebody know, what to do in such a situation?Thank 
>you very much in advance! Any tips are appreciated much!RegardsRoman
>_______________________________________________
>R-sig-Geo mailing list
>R-sig-Geo@r-project.org
>https://stat.ethz.ch/mailman/listinfo/r-sig-geo

____________________________________

Marcelino de la Cruz Rot
Depto. Biologia Vegetal
EUIT Agricola
Universidad Politecnica de Madrid

tel: 34 + 913365435
____________________________________  
	[[alternative HTML version deleted]]

