1CLIP(1gv) CLIP(1gv)
2
6 clip - Clip an OOGL object against planes or other surfaces
7
9 clip [-v axisx,y,z,...]
10 [-g value-or-point] [-l value-or-point]
11 [-s nstrips[,fraction]] [-e]
12 [-sph centerx,y,z,...] [-cyl centerx,y,z,...]
13 [ooglfile]
14
16 Clip, adapted from Daeron Meyer's ginsu module, allows clipping an OOGL
17 object against planes, spheres, or cylinders from the UNIX command
18 line. Its input can come from a file or standard input; output is
19 written to standard output.
20 Options specify a function of space position; the output is the portion
22 of the object where the function is greater or less than some given
23 value, or the portion lying between two values. Alternatively, an
24 object can be sliced into equally-spaced strips. Objects may be of any
25 dimension (but see the BUGS section).
26 Options are:
28 -g value-or-point
30 -l value-or-point
32 Select the portion of the object where the function is greater
33 than (-g) or less than (-l) the given value. If both are speci‐
34 fied, the result is the portion of the object satisfying both
35 conditions.
36 If, rather than a single number, the argument to -l or -g is a
38 point (a series of x,y,z,... values separated by commas, with no
39 embedded blanks), then the clipping surface is one chosen to
40 pass through that point.
41 -v axisx,y,z,...
43 Specifies a direction in space. For planar clipping (the
44 default), it's the plane normal direction; the clipping function
45 is the inner product between the direction vector and the point
46 on the object. For cylindrical clipping, -v specifies the
47 direction of the cylinder's axis; the clipping function is the
48 distance from the axis.
49 -sph centerx,y,z,...
51 Clip against spheres centered on x,y,z,.... The clipping func‐
52 tion is the distance from the given center. Coordinates must be
53 separated by commas without intervening spaces.
54 -cyl centerx,y,z,...
56 Clip against cylinders with an axis passing through cen‐
57 terx,y,z,..., with axis direction given by the -v option. The
58 clipping function is the distance from the axis.
59 -s nslices[,fraction]
61 Clip an object into a series of nslices ribbons spanning its
62 entire extent -- the range of function-values over the object.
63 Part of each ribbon is omitted; the fraction, default .5, sets
64 the width of the visible part of a ribbon compared to the ribbon
65 period. There are a total of (nslices+fraction-1) ribbon peri‐
66 ods across the object, so e.g. -s 2,.5 slices the object into
67 equal thirds, omitting the middle third. The output OOGL object
68 is a LIST of OFFs, one per ribbon.
69 -e Don't emit a clipped OOGL object, just print two numbers, list‐
71 ing the minimum and maximum function values for the object. If
72 -g or -l clipping options are specified, the object is clipped
73 before determining the function range. If none of the object
74 remains, clip prints "0 0".
75
77 To extract the portion of an object lying below the x+y+z=1 plane:
78 clip -l 1 -v 1,1,1 file.oogl > portion.oogl
80 To extract the portion of an object lying in the positive octant and
82 below the x+y+z=1 plane, we can pipe multiple instances of clip
83 together to find the intersection of several half-spaces:
84 clip -g 0 -v 1,0,0 file.oogl | \
86 clip -g 0 -v 0,1,0 | \
87 clip -g 0 -v 0,0,1 | \
88 clip -l 1 -v 1,1,1 > portion.oogl
89 To find the region lying between two surfaces (either above one and
91 below the other, or below the first and above the second), say the
92 planes 2x + y -.5z = 1 and y + 2z = 0:
93 echo "{ LIST"
95 clip -v 2,1,-.5 -g 1 file.oogl | clip -v 0,1,2 -l 0
96 clip -v 2,1,-.5 -l 1 file.oogl | clip -v 0,1,2 -g 0
97 echo "}"
98 We use pipelines to compute intersections, and a LIST to form their
100 union.
101
103 ginsu(1)
104
106 Uses anytooff(1) to convert input data to OFF format internally; this
107 can lose information. The only arbitrary-dimensional form accepted at
108 present is nOFF, not nSKEL or nMESH. However the four-dimensional
109 4OFF, 4QUAD, 4MESH, 4VECT, etc. formats should work.
110 Clip really only clips edges. If a curved clipping surface cuts an
112 edge twice, or removes only an interior portion of some polygon, clip
113 misses it entirely. Clipping against a curved surface yields a
114 straight edge (a chord of the ideal curved edge segment). This latter
115 failing might be fixed someday.
116Geometry Center 23 November 1994 CLIP(1gv)