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Thank you Adrian for your message (and the shortcut ! I haven't been
through) but the add of axes=F didn't change anything to me (R 2.9.0
and spatstat_1.15-4). <br>
So I'm still wondering if there is an existing implemented function in
R that could convert a binary mask to a polygon (which would be more
"handy" for me).<br>
<br>
So here is the goal of the work. If anyone has an idea of how this can
be done with an R package...<br>
<br>
I have a dataset on Golden Eagle breeding in the Alps. Along with data
on the breeding success of almost all territories each year, I have the
location of those territories' nests (a point pattern). Since the
population has increased (from 80 to 142 breeding pairs) and since I
have no accurate idea of home range sizes, I would have been interested
in getting an approximate territory size by a Dirichlet tesselation
(one of the reason why I used spatstat)<br>
.<br>
But, I cannot simply draw an arbitrary line around the study area (my
observation window) in order to "cut" the tesselation. Since the
population has increased, the shape of such polygon would fit with the
last years data but won't do it at the beginning of the survey. So I
wanted, for each year, to determine a treshold for the intensity of the
point pattern (with biologically relevant sigma values), retrieve all
the datas below that treshold, create an observation window with the
rest of it and calculate the tesselation on the point pattern.<br>
Then, use this tesselation along with data on habitat (vegetation,
temperatures, snow covers, etc.) under those polygons in order to
understand the settlement pattern and its consequences on breeding
pairs.<br>
<br>
If there is no other ways, I'll do that on ArcGis (sorry for swearing
on a list dedicated to free softwares) but with a 25 years or so
dataset, my lazyness would have had prefered to loop with R.<br>
<br>
Thanks again for your assistance.<br>
<br>
Alex<br>
<br>
<br>
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Adrian.Baddeley@csiro.au">Adrian.Baddeley@csiro.au</a> a écrit :
<blockquote
cite="mid:57DC18C299094D4299F837570C5DF1C502AA3B9522@EXWA-MBX01.nexus.csiro.au"
type="cite">
<pre wrap="">Alexandre VILLERS wrote:
</pre>
<blockquote type="cite">
<pre wrap="">I would like to create a new window for a point pattern in order to get
a tess object (dirichlet tessellation) from that same point pattern.
For the moment, here is an example of what I do:
</pre>
</blockquote>
<pre wrap=""><!---->
</pre>
<blockquote type="cite">
<pre wrap="">PPP<- rpoispp(100) #generate a point pattern
wind1<-density(PPP, sigma=0.1) #smoothed object of class im
wind2<-wind1 #copy the object
wind2$v<-ifelse(wind2$v<150, NA, wind1$v) #replace with NAs the value
# of pixel I don't want to keep (those whose intensity is < 150)
M<-as.owin(wind2) #convert the im object to a window
PPPd<-ppp(PPP$x,PPP$y, window=M) #the new point pattern with the new window
plot(dirichlet(PPPd)) #the result which did not convince me !
</pre>
</blockquote>
<pre wrap=""><!---->
This is a bug in plot.tess. The dirichlet command has correctly computed a tessellation, but the plot method for tessellations has included some strange black lines. To suppress the lines, use
plot(dirichlet(PPPd), axes=FALSE)
However it will take some more work to get a nice appearance for this plot. I will repair plot.tess in the next version (1.16-0) which will be out soon.
Incidentally, the following lines ...
</pre>
<blockquote type="cite">
<pre wrap="">wind2 <- wind1
wind2$v<-ifelse(wind2$v<150, NA, wind1$v)
M<-as.owin(wind2) #convert the im object to a window
</pre>
</blockquote>
<pre wrap=""><!---->
... could be replaced by
M <- levelset(wind1, 150, "<")
Adrian Baddeley
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</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Alexandre Villers
PhD Student
Team "Biodiversity"
Centre d'Etudes Biologiques de Chizé-CNRS UPR1934
79360 Beauvoir sur Niort
Phone +33 (0)5 49 09 96 13
Fax +33 (0)5 49 09 65 26</pre>
<br>
<br>
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