[R-sig-Geo] Help with anti-clockwise polygon in owin

Thu Jan 8 20:04:31 CET 2009

Dear list,
I have a point pattern that consists of  wells on an island.  I am  
interested doing some exploratory point pattern analysis on this data  
(such as Gest in spatstat).  The island as you can imagine is an  
irregular polygon defined by 1815 points.  When I try to create the  
observation window for the point pattern in spatstat using

owin(x=range(westcoords$X), y=range(westcoords$Y),  
poly=list(x=westcoords$X, y=westcoords$Y))
where westcoords are the coordinated of the polygon
I get:
Error in owin(x = range(westcoords$X), y = range(westcoords$Y), poly =  
list(x = westcoords$X,  :
   Area of polygon is negative - maybe traversed in wrong direction?

Since the origin of the coordinates is a shapefile I created myself,  
how can I get around this "traversed in the wrong direction" problem?   
I can make the data this is based on available if anyone would need it.

I'm using R 2.8.1 on a Mac with Leopard OS

Corey Sparks
Assistant Professor
Department of Demography and Organization Studies
University of Texas at San Antonio
One UTSA Circle
San Antonio, TX 78249
210 458 6858
corey.sparks at utsa.edu

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