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doc tweaks for skin(), faster 2d hull()
This commit is contained in:
Adrian Mariano
parent
5ce8ba4728
commit
863c410404
2 changed files with 71 additions and 68 deletions
85
hull.scad
85
hull.scad
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@ -74,6 +74,15 @@ module hull_points(points, fast=false) {
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}
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function _backtracking(i,points,h,t,m) =
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m<t || _is_cw(points[i], points[h[m-1]], points[h[m-2]]) ? m :
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_backtracking(i,points,h,t,m-1) ;
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// clockwise check (2d)
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function _is_cw(a,b,c) = cross(a-c,b-c)<=0;
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// Function: hull2d_path()
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// Usage:
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// hull2d_path(points)
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@ -85,34 +94,42 @@ module hull_points(points, fast=false) {
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// path = hull2d_path(pts);
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// move_copies(pts) color("red") sphere(1);
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// polygon(points=pts, paths=[path]);
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// Code based on this method:
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// https://www.hackerearth.com/practice/math/geometry/line-sweep-technique/tutorial/
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//
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function hull2d_path(points) =
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assert(is_path(points,2),"Invalid input to hull2d_path")
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len(points) < 2 ? []
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: len(points) == 2 ? [0,1]
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: let(tri=noncollinear_triple(points, error=false))
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tri == [] ? _hull_collinear(points)
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: let(
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remaining = [ for (i = [0:1:len(points)-1]) if (i != tri[0] && i!=tri[1] && i!=tri[2]) i ],
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ccw = triangle_area(points[tri[0]], points[tri[1]], points[tri[2]]) > 0,
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polygon = ccw ? [tri[0],tri[1],tri[2]] : [tri[0],tri[2],tri[1]]
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) _hull2d_iterative(points, polygon, remaining);
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// Adds the remaining points one by one to the convex hull
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function _hull2d_iterative(points, polygon, remaining, _i=0) =
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(_i >= len(remaining))? polygon : let (
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// pick a point
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i = remaining[_i],
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// find the segments that are in conflict with the point (point not inside)
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conflicts = _find_conflicting_segments(points, polygon, points[i])
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// no conflicts, skip point and move on
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) (len(conflicts) == 0)? _hull2d_iterative(points, polygon, remaining, _i+1) : let(
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// find the first conflicting segment and the first not conflicting
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// conflict will be sorted, if not wrapping around, do it the easy way
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polygon = _remove_conflicts_and_insert_point(polygon, conflicts, i)
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) _hull2d_iterative(points, polygon, remaining, _i+1);
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:
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assert(is_path(points,2))
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assert(len(points)>=3, "Point list must contain at least 3 points.")
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let( n = len(points),
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ip = sortidx(points) )
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// lower hull points
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let( lh =
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[ for( i = 2,
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k = 2,
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h = [ip[0],ip[1]]; // current list of hull point indices
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i <= n;
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k = i<n ? _backtracking(ip[i],points,h,2,k)+1 : k,
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h = i<n ? [for(j=[0:1:k-2]) h[j], ip[i]] : [],
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i = i+1
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) if( i==n ) h ][0] )
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// concat lower hull points with upper hull ones
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[ for( i = n-2,
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k = len(lh),
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t = k+1,
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h = lh; // current list of hull point indices
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i >= -1;
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k = i>=0 ? _backtracking(ip[i],points,h,t,k)+1 : k,
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h = [for(j=[0:1:k-2]) h[j], if(i>0) ip[i]],
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i = i-1
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) if( i==-1 ) h ][0] ;
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function _hull_collinear(points) =
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let(
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@ -124,30 +141,6 @@ function _hull_collinear(points) =
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) [min_i, max_i];
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function _find_conflicting_segments(points, polygon, point) = [
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for (i = [0:1:len(polygon)-1]) let(
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j = (i+1) % len(polygon),
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p1 = points[polygon[i]],
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p2 = points[polygon[j]],
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area = triangle_area(p1, p2, point)
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) if (area < 0) i
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];
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// remove the conflicting segments from the polygon
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function _remove_conflicts_and_insert_point(polygon, conflicts, point) =
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(conflicts[0] == 0)? let(
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nonconflicting = [ for(i = [0:1:len(polygon)-1]) if (!in_list(i, conflicts)) i ],
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new_indices = concat(nonconflicting, (nonconflicting[len(nonconflicting)-1]+1) % len(polygon)),
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polygon = concat([ for (i = new_indices) polygon[i] ], point)
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) polygon : let(
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before_conflicts = [ for(i = [0:1:min(conflicts)]) polygon[i] ],
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after_conflicts = (max(conflicts) >= (len(polygon)-1))? [] : [ for(i = [max(conflicts)+1:1:len(polygon)-1]) polygon[i] ],
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polygon = concat(before_conflicts, point, after_conflicts)
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) polygon;
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// Function: hull3d_faces()
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// Usage:
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// hull3d_faces(points)
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54
skin.scad
54
skin.scad
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@ -47,31 +47,29 @@
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// profiles that you specify. It is generally best if the triangles forming your polyhedron
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// are approximately equilateral. The `slices` parameter specifies the number of slices to insert
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// between each pair of profiles, either a scalar to insert the same number everywhere, or a vector
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// to insert a different number between each pair. To resample the profiles you can use set
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// `refine=N` which will place `N` points on each edge of your profile. This has the effect of
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// multiplying the number of points by N, so a profile with 8 points will have 8*N points after
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// refinement. Note that when dealing with continuous curves it is always better to adjust the
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// to insert a different number between each pair.
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// .
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// Resampling may occur, depending on the `method` parameter, to make profiles compatible.
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// To force (possibly additional) resampling of the profiles to increase the point density you can set `refine=N`, which
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// will multiply the number of points on your profile by `N`. You can choose between two resampling
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// schemes using the `sampling` option, which you can set to `"length"` or `"segment"`.
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// The length resampling method resamples proportional to length.
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// The segment method divides each segment of a profile into the same number of points.
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// This means that if you refine a profile with the "segment" method you will get N points
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// on each edge, but if you refine a profile with the "length" method you will get new points
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// distributed around the profile based on length, so small segments will get fewer new points than longer ones.
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// A uniform division may be impossible, in which case the code computes an approximation, which may result
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// in arbitrary distribution of extra points. See `subdivide_path` for more details.
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// Note that when dealing with continuous curves it is always better to adjust the
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// sampling in your code to generate the desired sampling rather than using the `refine` argument.
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// .
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// Two methods are available for resampling, `"length"` and `"segment"`. Specify them using
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// the `sampling` argument. The length resampling method resamples proportional to length.
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// The segment method divides each segment of a profile into the same number of points.
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// A uniform division may be impossible, in which case the code computes an approximation.
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// See `subdivide_path` for more details.
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//
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// You can choose from four methods for specifying alignment for incommensurate profiles.
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// The available methods are `"distance"`, `"tangent"`, `"direct"` and `"reindex"`.
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// It is useful to distinguish between continuous curves like a circle and discrete profiles
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// like a hexagon or star, because the algorithms' suitability depend on this distinction.
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// .
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// The "direct" and "reindex" methods work by resampling the profiles if necessary. As noted above,
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// for continuous input curves, it is better to generate your curves directly at the desired sample size,
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// but for mapping between a discrete profile like a hexagon and a circle, the hexagon must be resampled
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// to match the circle. You can do this in two different ways using the `sampling` parameter. The default
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// of `sampling="length"` approximates a uniform length sampling of the profile. The other option
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// is `sampling="segment"` which attempts to place the same number of new points on each segment.
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// If the segments are of varying length, this will produce a different result. Note that "direct" is
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// the default method. If you simply supply a list of compatible profiles it will link them up
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// The default method for aligning profiles is `method="direct"`.
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// If you simply supply a list of compatible profiles it will link them up
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// exactly as you have provided them. You may find that profiles you want to connect define the
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// right shapes but the point lists don't start from points that you want aligned in your skinned
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// polyhedron. You can correct this yourself using `reindex_polygon`, or you can use the "reindex"
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@ -79,12 +77,25 @@
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// in the polyhedron---in will produce the least twisted possible result. This algorithm has quadratic
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// run time so it can be slow with very large profiles.
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// .
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// When the profiles are incommensurate, the "direct" and "reindex" resampling them to match. As noted above,
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// for continuous input curves, it is better to generate your curves directly at the desired sample size,
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// but for mapping between a discrete profile like a hexagon and a circle, the hexagon must be resampled
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// to match the circle. When you use "direct" or "reindex" the default `sampling` value is
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// of `sampling="length"` to approximate a uniform length sampling of the profile. This will generally
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// produce the natural result for connecting two continuously sampled profiles or a continuous
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// profile and a polygonal one. However depending on your particular case,
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// `sampling="segment"` may produce a more pleasing result. These two approaches differ only when
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// the segments of your input profiles have unequal length.
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// .
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// The "distance" and "tangent" methods work by duplicating vertices to create
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// triangular faces. The "distance" method finds the global minimum distance method for connecting two
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// profiles. This algorithm generally produces a good result when both profiles are discrete ones with
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// a small number of vertices. It is computationally intensive (O(N^3)) and may be
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// slow on large inputs. The resulting surfaces generally have curved faces, so be
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// sure to select a sufficiently large value for `slices` and `refine`.
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// sure to select a sufficiently large value for `slices` and `refine`. Note that for
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// this method, `sampling` must be set to `"segment"`, and hence this is the default setting.
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// Using sampling by length would ignore the repeated vertices and ruin the alignment.
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// .
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// The `"tangent"` method generally produces good results when
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// connecting a discrete polygon to a convex, finely sampled curve. It works by finding
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// a plane that passed through each edge of the polygon that is tangent to
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@ -92,9 +103,8 @@
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// all of the tangent points from each other. It connects all of the points of the curve to the corners of the discrete
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// polygon using triangular faces. Using `refine` with this method will have little effect on the model, so
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// you should do it only for agreement with other profiles, and these models are linear, so extra slices also
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// have no effect. For best efficiency set `refine=1` and `slices=0`. When you use refinement with either
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// of these methods, it is always the "segment" based resampling described above. This is necessary because
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// sampling by length will ignore the repeated vertices and break the alignment.
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// have no effect. For best efficiency set `refine=1` and `slices=0`. As with the "distance" method, refinement
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// must be done using the "segment" sampling scheme to preserve alignment across duplicated points.
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// .
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// It is possible to specify `method` and `refine` as arrays, but it is important to observe
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// matching rules when you do this. If a pair of profiles is connected using "tangent" or "distance"
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