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Merge pull request #492 from RonaldoCMP/master

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Test for convexity of 3d polygons
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Revar Desmera 2021-04-07 00:25:36 -07:00 committed by GitHub
commit a1ae5a5057
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2 changed files with 19 additions and 16 deletions
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34
geometry.scad
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@ -1074,6 +1074,7 @@ function distance_from_plane(plane, point) =
let( plane = normalize_plane(plane) )
point3d(plane)* point - plane[3];
// Returns [POINT, U] if line intersects plane at one point.
// Returns [LINE, undef] if the line is on the plane.
// Returns undef if line is parallel to, but not on the given plane.
@ -1596,7 +1597,6 @@ function circle_circle_tangents(c1,r1,c2,r2,d1,d2) =
];
// Function: circle_line_intersection()
// Usage:
// isect = circle_line_intersection(c,r,line,<bounded>,<eps>);
@ -1629,7 +1629,6 @@ function circle_line_intersection(c,r,line,d,bounded=false,eps=EPSILON) =
let( offset = sqrt(r*r-d*d),
uvec=unit(line[1]-line[0])
) [closest-offset*uvec, closest+offset*uvec]
)
[for(p=isect)
if ((!bounded[0] || (p-line[0])*(line[1]-line[0])>=0)
@ -1637,7 +1636,6 @@ function circle_line_intersection(c,r,line,d,bounded=false,eps=EPSILON) =
// Section: Pointlists
@ -1758,27 +1756,31 @@ function polygon_area(poly, signed=false) =
// Usage:
// is_convex_polygon(poly);
// Description:
// Returns true if the given 2D polygon is convex. The result is meaningless if the polygon is not simple (self-intersecting).
// If the points are collinear the result is true.
// Returns true if the given 2D or 3D polygon is convex.
// The result is meaningless if the polygon is not simple (self-intersecting) or non coplanar.
// If the points are collinear an error is generated.
// Arguments:
// poly = Polygon to check.
// Example:
// is_convex_polygon(circle(d=50)); // Returns: true
// is_convex_polygon(rot([50,120,30], p=path3d(circle(1,$fn=50)))); // Returns: true
// Example:
// spiral = [for (i=[0:36]) let(a=-i*10) (10+i)*[cos(a),sin(a)]];
// is_convex_polygon(spiral); // Returns: false
function is_convex_polygon(poly) =
assert(is_path(poly,dim=2), "The input should be a 2D polygon." )
let( l = len(poly) )
len([for( i = l-1,
c = cross(poly[(i+1)%l]-poly[i], poly[(i+2)%l]-poly[(i+1)%l]),
s = sign(c);
i>=0 && sign(c)==s;
i = i-1,
c = i<0? 0: cross(poly[(i+1)%l]-poly[i],poly[(i+2)%l]-poly[(i+1)%l]),
s = s==0 ? sign(c) : s
) i
])== l;
assert(is_path(poly), "The input should be a 2D or 3D polygon." )
let( lp = len(poly),
p0 = poly[0] )
assert( lp>=3 , "A polygon must have at least 3 points" )
let( crosses = [for(i=[0:1:lp-1]) cross(poly[(i+1)%lp]-poly[i], poly[(i+2)%lp]-poly[(i+1)%lp]) ] )
len(p0)==2
? assert( !approx(max(crosses)) && !approx(min(crosses)), "The points are collinear" )
min(crosses) >=0 || max(crosses)<=0
: let( prod = crosses*sum(crosses),
minc = min(prod),
maxc = max(prod) )
assert( !approx(maxc-minc), "The points are collinear" )
minc>=0 || maxc<=0;
// Function: polygon_shift()

1
tests/test_geometry.scad
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@ -844,6 +844,7 @@ module test_polygon_area() {
module test_is_convex_polygon() {
assert(is_convex_polygon([[1,1],[-1,1],[-1,-1],[1,-1]]));
assert(is_convex_polygon(circle(r=50,$fn=1000)));
assert(is_convex_polygon(rot([50,120,30], p=path3d(circle(1,$fn=50)))));
assert(!is_convex_polygon([[1,1],[0,0],[-1,1],[-1,-1],[1,-1]]));
}
*test_is_convex_polygon();