cutSpace: separate a 3D-pointcloud by a hyperplane

In zarquon42b/Morpho: Calculations and Visualisations Related to Geometric Morphometrics

separate a 3D-pointcloud by a hyperplane

Description

separate a 3D-pointcloud by a hyperplane

Usage

cutSpace(pointcloud, v1, v2 = NULL, v3 = NULL, normal = NULL, upper = TRUE)

Arguments

pointcloud	numeric n x 3 matrix
v1	numeric vector of length=3 specifying a point on the separating plane
v2	numeric vector of length=3 specifying a point on the separating plane
v3	numeric vector of length=3 specifying a point on the separating plane
normal	plane normal (overrides specification by v2 and v3)
upper	logical specify whether the points above or below the plane are to be reported as TRUE.

Details

As above and below are specified by the normal calculated from (v2-v1) \times (v3-v1), where \times denotes the vector crossproduct. This means the normal points "upward" when viewed from the positon where v1, v2 and v3 are arranged counter-clockwise. Thus, which side is "up" depends on the ordering of v1, v2 and v3.

Value

logical vector of length n. Reporting for each point if it is above or below the hyperplane

Examples

data(nose)
v1 <- shortnose.lm[1,]
v2 <- shortnose.lm[2,]
v3 <- shortnose.lm[3,]
pointcloud <- vert2points(shortnose.mesh)
upper <- cutSpace(pointcloud, v1, v2, v3)
## Not run: 
require(rgl)
normal <- crossProduct(v2-v1,v3-v1)
zeroPro <- points2plane(rep(0,3),v1,normal)
## get sign of normal displacement from zero
sig <- sign(crossprod(-zeroPro,normal))
d <- sig*norm(zeroPro,"2")
planes3d(normal[1],normal[2],normal[3],d=d)
points3d(pointcloud[upper,])

## End(Not run)

zarquon42b/Morpho documentation built on Jan. 28, 2024, 2:11 p.m.