| Title: | Calculate Area of Triangles and Polygons |
| Version: | 0.2.0 |
| Description: | Calculate the area of triangles and polygons using the shoelace formula. Area may be signed, taking into account path orientation, or unsigned, ignoring path orientation. The shoelace formula is described at https://en.wikipedia.org/wiki/Shoelace_formula. |
| License: | GPL-3 |
| Encoding: | UTF-8 |
| LazyData: | true |
| RoxygenNote: | 7.2.3 |
| Depends: | R (≥ 4.1.0) |
| URL: | https://github.com/hypertidy/area |
| BugReports: | https://github.com/hypertidy/area/issues |
| LinkingTo: | cpp11 |
| Suggests: | testthat |
| NeedsCompilation: | yes |
| Packaged: | 2023-12-21 10:53:54 UTC; gdal |
| Author: | Michael Sumner 
[aut, cre, cph] |
| Maintainer: | Michael Sumner <mdsumner@gmail.com> |
| Repository: | CRAN |
| Date/Publication: | 2023-12-21 11:20:02 UTC |
area: Calculate Area of Triangles and Polygons
Description
Calculate the area of triangles and polygons using the shoelace formula. Area may be signed, taking into account path orientation, or unsigned, ignoring path orientation. The shoelace formula is described at https://en.wikipedia.org/wiki/Shoelace_formula.
Author(s)
Maintainer: Michael Sumner mdsumner@gmail.com (ORCID) [copyright holder]
See Also
Useful links:
Planar straight line graphs and triangulations
Description
A minimal mesh with one hole mm and a map of Tasmania with multiple
holes in planar straight line graph format from the RTriangle package.
Details
mm_tri is a triangulated form of mm in RTriangle triangulation format.
The HOLE property is not yet set WIP.
Examples
str(mm)
Area of polygon
Description
Calculate polygon area from a matrix of a closed polygon. Closed means that the first coordinate is the same as the last.
Usage
polygon_area(x, signed = FALSE)
Arguments
x |
polygon in xy matrix |
signed |
defaults to |
Details
Only one polygon can be input. We are using the normal definition of polygon which is a plane figure described by straight line segments.
Currently inputs are not checked but are assumed to have the last coordinate as a copy of the first aka 'closed'.
If signed = FALSE the absolute value of area is returned, otherwise the
sign reflects path orientation. Positive means counter-clockwise orientation.
The algorithm used was once on the internet at "w w w .cs.tufts.edu/comp/163/OrientationTests.pdf"
Value
numeric vector of area
Examples
x <- c(2, 10, 8, 11, 7, 2)
y <- c(7, 1, 6, 7, 10, 7)
polygon_area(cbind(x, y), signed = TRUE)
xy <-
cbind(x = c(2.3, 1.5, 2.4, 4.5, 4.6, 5.4, 7.6, 8.6, 7.4, 5.1, 2.3),
y = c(-1.4, 7.3, 22.2, 22.5, 14.4, 11.8, 16.4, 5, 0.8, -1.6, -1.4))
polygon_area(xy)
## xy is clockwise so area is negative
polygon_area(xy, signed = TRUE)
polygon_area(xy[nrow(xy):1, ], signed = TRUE)
## Rosetta code example
## https://rosettacode.org/wiki/Shoelace_formula_for_polygonal_area
m <- rbind(c(3,4), c(5,11), c(12,8), c(9,5), c(5,6))
p <- m[c(1:nrow(m), 1), ] ## close it
polygon_area(p)
Area of triangles
Description
Calculate triangle area from a matrix of coordinates. Triangles are composed of three coordinates, so the matrix should have this as triplets of rows one after the other.
Usage
triangle_area(x, signed = FALSE)
Arguments
x |
coordinates x,y triplets matrix where 'nrow(x) = ntriangles*3' |
signed |
defaults to |
Details
If signed = FALSE the absolute value of area is returned, otherwise the
sign reflects path orientation. Positive means counter-clockwise orientation.
The algorithm was once documented at 'w w w cs.tufts.edu/comp/163/OrientationTests.pdf'
Value
numeric vector of area
Examples
sum(triangle_area(mm_tri$P[t(mm_tri$T), ]))