[R] Using GIS data in R

[Zuofeng Shang]

Hi Rolf,

Thanks very much for suggestions! Sorry if I made my question not very 
clear.

The context is as follows. I have a set of locations with coordinates 
(latitude and longitude)
from Texas region. Some of the locations are within Texas while some of 
them are not.
I am trying to find those locations within Texas by looking at if the 
coordinate of each location
is within the boundary of Texas.

Now I agree with you that the boundary of Texas is polygon although it 
looks like "irregular".
I find your previous post very helpful. inside.owin() will do the job 
but I have to figure out
the boundary (as a polygon) of Texas. Since I do not have the shapefile 
of Texas, this will be
difficult for me. I am not sure if the shapefile of the US states are 
available in R. If it not,
how can I get the shapefiles? Thanks a lot for kind help!

Best regards,
Jeff




> On 21/11/11 08:01, JeffND wrote:
>> Hi Rolf,
>>
>> I have a similar question. I want to test whether a point with certain
>> coordinates is inside
>> a state, say Texas. It seems that inside.owin() only works for testing if a
>> point lies in a
>> regular region, say a polygon. Since Texas has irregular boundary, how do we
>> achieve this?
>> Or there is some alternative way we can use.
>>
>> Thanks!
>> Jeff
>>
>> --
>> View this message in context: http://r.789695.n4.nabble.com/Using-GIS-data-in-R-tp1748266p4089242.html
>> Sent from the R help mailing list archive at Nabble.com.
> It would be nice to have some context ... nabble strikes again.
>
> But to get to your question:  How do you think the boundary of Texas
> (irregular as it may be) is specified?  I expect that it is specified as
> a polygon!!!  It may be *very* ``poly'' --- i.e. have a large number of
> edges --- but it's still a polygon and inside.owin() will still work on it.
>
> Have a look at the data set "nbfires" in the spatstat package.  New
> Brunswick has an ``irregular boundary'' too!
>
> Have you *tried* making your specification of Texas into an owin object?
> Follow the instructions in the vignette given by:
>
>       vignette("shapefiles")
>
>       cheers,
>
>           Rolf Turner