gpc-polyfile: Read/Write polygon data

In rgeos: Interface to Geometry Engine - Open Source ('GEOS')

Read/Write polygon data

Description

Read/Write polygon and contour information from/to a text file.

Usage

read.polyfile(filename, nohole = TRUE)
write.polyfile(poly, filename = "GPCpoly.txt")

Arguments

filename	the name of the file (a character string) from/to which data should be read/written.
nohole	Is this a polygon without holes?
poly	an object of class "gpc.poly"

Details

The text file representation of a polygon is of the following format:

<number of contours>
<number of points in first contour>
x1 y1
x2 y2
...
<number of points in second contour>
x1 y1
x2 y2
...

For example, a data file for a polygon with 2 contours (a four-sided object and a triangle) might look like:

2
4
1.0 1.0
1.0 2.0
3.4 3.21
10 11.2
3
21.0 11.2
22.3 99.2
4.5 5.4

The vertices of the polygon can be ordered either clockwise or counter-clockwise.

If a polygon has contours which are holes, then the format is slightly different. Basically, a flag is set to indicate that a particular contour is a hole. The format is

<number of contours>
<number of points in first contour>
<hole flag>
x1 y1
x2 y2
...
<number of points in second contour>
<hole flag>
x1 y1
x2 y2
...

The hole flag is either 1 to indicate a hole, or 0 for a regular contour. For example, a four-sided polygon with a triangular hole would be written as:

2
3
1
4.0 4.0
6.0 5.0
5.0 6.0
4
0
2.0 1.0
8.0 2.0
7.0 9.0
1.0 7.0

Value

If nohole is TRUE (the default) read.polyfile returns an object of class "gpc.poly.nohole". This object has the hole flag set to FALSE for all contours. If nohole is FALSE, then an object of class "gpc.poly" is returned.

write.polyfile does not return anything useful.

Author(s)

Roger D. Peng

See Also

gpc.poly-class, gpc.poly.nohole-class

Examples

## None right now.

rgeos documentation built on July 9, 2023, 3:08 p.m.