[R] spatstat regression troubles

Gregory Ryslik rsaber at comcast.net
Sat Apr 16 05:50:25 CEST 2011

Hi Everyone,

I am trying to figure out the spatstat package for the first time and am having some trouble. Unfortunately, I can't post my data set but I'll hopefully post enough details for some help.

I want to model the intensity of a spatial point process using 2 covariates from my data. After reading through the documentation, I have successfully created 2 "ppp" objects. The first ppp object is a list of coordinates where people exist and the second is where people do not exist as follows:

> people_exist
 planar point pattern: 944 points 
window: rectangle = [73, 135] x [18, 54] units  
> people_empty
 planar point pattern: 2828 points 
window: rectangle = [73, 135] x [18, 54] units  

Now, I also have observed values for two covariates, Z1 and Z2 for both the 944 and 2828 points in dataframe form. Finally, following the documentation, I was able to create one quadrature Q, with 944 points and 2828 dummy points that correctly takes the points where we had an event (people_exist) and the points where we don't have an event (people_empty).

> people_quadrature
Quadrature scheme
944 data points,  2828 dummy points
Total weight  1098.64 

How do I use the Quadrature to model my intensity based off of those two covariates and an intercept term alpha? In mathematical terms, if \lambda is my intensity function, I want to estimate \lambda(s;b) = exp(alpha + b_1 * Z_1 + b_2 * Z_2).

Thank you for your help! I really appreciate it.

Kind regards,
Greg R.

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