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Correction of some coplanarity tests and reorganization

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RonaldoCMP 2021-04-11 09:02:08 +01:00
parent 2dcbfeee11
commit 5c6181d4d4
1 changed files with 38 additions and 31 deletions
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geometry.scad
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@ -912,36 +912,40 @@ function _eigenvals_symm_3(M) =
[ e1, e2, e3 ];
// i-th normalized eigenvector of 3x3 symmetrical matrix M from its eigenvalues
// the i-th normalized eigenvector of a 3x3 symmetrical matrix M from its eigenvalues
// using Cayley–Hamilton theorem according to:
// https://en.wikipedia.org/wiki/Eigenvalue_algorithm
function _eigenvec_symm_3(M,evals,i=0) =
let( A = (M - evals[(i+1)%3]*ident(3)) * (M - evals[(i+2)%3]*ident(3)) ,
k = max_index( [for(i=[0:2]) norm(A[i]) ])
)
norm(A[k])<EPSILON ? ident(3)[k] : A[k]/norm(A[k]);
let(
I = ident(3),
A = (M - evals[(i+1)%3]*I) * (M - evals[(i+2)%3]*I) ,
k = max_index( [for(i=[0:2]) norm(A[i]) ])
)
norm(A[k])<EPSILON ? I[k] : A[k]/norm(A[k]);
// eigenvalues of the covariance matrix of points
function _covariance_evals(points) =
let( pm = sum(points)/len(points), // mean point
Y = [ for(i=[0:len(points)-1]) points[i] - pm ],
M = transpose(Y)*Y , // covariance matrix
evals = _eigenvals_symm_3(M) )
[pm, evals, M ];
// finds the eigenvector corresponding to the smallest eigenvalue of the covariance matrix of a pointlist
// returns the mean of the points, the eigenvector and the greatest eigenvalue
function _covariance_evec_eval(points) =
let( pm = sum(points)/len(points), // mean point
Y = [ for(i=[0:len(points)-1]) points[i] - pm ],
M = transpose(Y)*Y , // covariance matrix
evals = _eigenvals_symm_3(M), // eigenvalues in decreasing order
evec = _eigenvec_symm_3(M,evals,i=2) )
[pm, evec, evals[0] ];
// Function: plane_from_points()
// Usage:
// plane_from_points(points, <fast>, <eps>);
// Description:
// Given a list of 3 or more coplanar 3D points, returns the coefficients of the normalized cartesian equation of a plane,
// that is [A,B,C,D] where Ax+By+Cz=D is the equation of the plane where norm([A,B,C])=1.
// that is [A,B,C,D] where Ax+By+Cz=D is the equation of the plane and norm([A,B,C])=1.
// If `fast` is false and the points in the list are collinear or not coplanar, then `undef` is returned.
// If `fast` is true, the polygon coplanarity check is skipped and a best fitted plane is returned.
// Arguments:
// points = The list of points to find the plane of.
// fast = If true, don't verify that all points in the list are coplanar. Default: false
// fast = If true, don't verify the point coplanarity. Default: false
// eps = Tolerance in geometric comparisons. Default: `EPSILON` (1e-9)
// Example(3D):
// xyzpath = rot(45, v=[-0.3,1,0], p=path3d(star(n=6,id=70,d=100), 70));
@ -956,14 +960,13 @@ function plane_from_points(points, fast=false, eps=EPSILON) =
? let( plane = plane3pt(points[0],points[1],points[2]) )
plane==[] ? undef : plane
: let(
cov_evals = _covariance_evals(points),
pm = cov_evals[0],
evals = cov_evals[1],
M = cov_evals[2],
evec = _eigenvec_symm_3(M,evals,i=2) )
// echo(error_points_plane= abs(max(points*evec)-pm*evec), limit=eps)
!fast && abs(max(points*evec)-pm*evec)>eps*evals[0] ? undef :
[ each evec, pm*evec] ;
covmix = _covariance_evec_eval(points),
pm = covmix[0],
evec = covmix[1],
eval0 = covmix[2],
plane = [ each evec, pm*evec] )
!fast && _pointlist_greatest_distance(points,plane)>eps*eval0 ? undef :
plane ;
// Function: plane_from_polygon()
@ -1291,11 +1294,17 @@ function coplanar(points, eps=EPSILON) =
len(points)<=2 ? false
: let( ip = noncollinear_triple(points,error=false,eps=eps) )
ip == [] ? false :
let(
plane = plane3pt(points[ip[0]],points[ip[1]],points[ip[2]]),
normal = point3d(plane),
pt_nrm = points*normal )
abs(max(max(pt_nrm)-plane[3], -min(pt_nrm)+plane[3])) < eps;
let( plane = plane3pt(points[ip[0]],points[ip[1]],points[ip[2]]) )
_pointlist_greatest_distance(points,plane) < eps;
// the maximum distance from points to the plane
function _pointlist_greatest_distance(points,plane) =
let(
normal = point3d(plane),
pt_nrm = points*normal
)
abs(max( max(pt_nrm) - plane[3], -min(pt_nrm)+plane[3])) / norm(normal);
// Function: points_on_plane()
@ -1311,9 +1320,7 @@ function points_on_plane(points, plane, eps=EPSILON) =
assert( _valid_plane(plane), "Invalid plane." )
assert( is_matrix(points,undef,3) && len(points)>0, "Invalid pointlist." ) // using is_matrix it accepts len(points)==1
assert( is_finite(eps) && eps>=0, "The tolerance should be a positive number." )
let( normal = point3d(plane),
pt_nrm = points*normal )
abs(max( max(pt_nrm) - plane[3], -min(pt_nrm)+plane[3]))< eps*norm(normal);
_pointlist_greatest_distance(points,plane) < eps;
// Function: in_front_of_plane()