[R] Determine if a set of x and y-latitude points are inside of a polygon using R

[David L Carlson]

Give us reproducible data using dput(). There are easier ways to accomplish what you want in R. The overwriting problem stems from the fact that you have a double loop so each iteration of the outer loop overwrites the data produced in the inner loop. 

Also your if/else specification should be producing the following error message:

Error: unexpected 'else' in "else"

Since else needs to be on the same line as the closing curly brace for if:

if (M>1) {
        Bounds$T[i] = M
        } else
        {
        Bounds$T[i] = M
        }

And why use if/else at all since you execute Bounds$T[i] = M either way?

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Shawn Adderly
Sent: Wednesday, April 27, 2016 3:08 AM
To: r-help at r-project.org
Subject: [R] Determine if a set of x and y-latitude points are inside of a polygon using R

Objective: Determine if a set of x and y-latitude points are inside of
a polygon using R.

Lets say I have 9 polygons. Where I have labeled the polygons to be
checked from 1-9. The problem I’m running into is running the
point.in.polygon to check if those points are in one of several
polygons, as my code overwrites the result.

To accomplish this I am using the R-built in function called
point.in.polygon. Point.in.polygon takes the x, and y lat/lon points,
and the polygon boundaries.

Here is the code I've written thus far:

 require("SDMTools")
 require("sp")

 #b is the polygon that I'm referring
 for (b in 1:9)
 {
    D <- subset(Bounds, Polygon == b)
    for (i in 1:length(Bounds$latitude))
    {
    M = point.in.polygon(Bounds$latitude[i], Bounds$longitude[i], D$PY,D$PX)
       if (M>1) {
        Bounds$T[i] = M
        }
        else
        {
        Bounds$T[i] = M
        }
        }
    }


Minimal Dataset:

 Latitude Longitude Polygon Latitude Polygon Longitude Polygon
 38.65485 -121.4965 38.43768 -121.4018 1
 38.562 -121.4768 38.56559 -121.4018 1
 38.7011 -121.3018 38.57065 -121.5141 1
 38.62568 -121.3198 38.56559 -121.5141 1
 38.60253 -121.2899 38.563459 -121.5141 2
 38.28272 -121.2969 38.56359 -121.5141 2
 38.64286 -121.2204 38.54065 -121.515 2
 38.67442 -121.5105 38.57065 -121.515

______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.