📄 qhull.txt
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the facet is greater than 'Vn'.
Without merging, the default value for 'Vn' is the
round-off error ('En'). With merging, the default
value is the pre-merge centrum ('C-n') in 2-d or
3--d, or three times that in other dimensions. If
the outside width is specified ('Wn'), the maximum,
default value for 'Vn' is 'Wn'.
Un Maximum distance below a facet for a point to be
coplanar to the facet. The default value is 'Vn'.
Wn Minimum outside width of the hull. Points are
added to the convex hull only if they are clearly
outside of a facet. A point is outside of a facet
if its distance to the facet is greater than 'Wn'.
The normal value for 'Wn' is 'En'. If the user
specifies pre-merging and does not set 'Wn', than
'Wn' is set to the premerge 'Cn' and maxco-
ord*(1-An).
Additional input/output formats
Fa Print area for each facet. For Delaunay triangula-
tions, the area is the area of the triangle. For
Voronoi diagrams, the area is the area of the dual
facet. Use 'PAn' for printing the n largest
facets, and option 'PFn' for printing facets larger
than 'n'.
The area for non-simplicial facets is the sum of
the areas for each ridge to the centrum. Vertices
far below the facet's hyperplane are ignored. The
reported area may be significantly less than the
actual area.
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FA Compute the total area and volume for option 's'.
It is an approximation for non-simplicial facets
(see 'Fa').
Fc Print coplanar points for each facet. The output
starts with the number of facets. Then each facet
is printed one per line. Each line is the number
of coplanar points followed by the point ids.
Option 'Qi' includes the interior points. Each
coplanar point (interior point) is assigned to the
facet it is furthest above (resp., least below).
FC Print centrums for each facet. The output starts
with the dimension followed by the number of
facets. Then each facet centrum is printed, one
per line.
Fd Read input in cdd format with homogeneous points.
The input starts with comments. The first comment
is reported in the summary. Data starts after a
"begin" line. The next line is the number of
points followed by the dimension+1 and "real" or
"integer". Then the points are listed with a
leading "1" or "1.0". The data ends with an "end"
line.
For halfspaces ('Fd Hn,n,...'), the input format is
the same. Each halfspace starts with its offset.
The sign of the offset is the opposite of Qhull's
convention.
FD Print normals ('n', 'Fo', 'Fi') or points ('p') in
cdd format. The first line is the command line
that invoked Qhull. Data starts with a "begin"
line. The next line is the number of normals or
points followed by the dimension+1 and "real".
Then the normals or points are listed with the
offset before the coefficients. The offset for
points is 1.0. The offset for normals has the
opposite sign. The data ends with an "end" line.
FF Print facets (as in 'f') without printing the
ridges.
Fi Print inner planes for each facet. The inner plane
is below all vertices.
Fi Print separating hyperplanes for bounded, inner
regions of the Voronoi diagram. The first line is
the number of ridges. Then each hyperplane is
printed, one per line. A line starts with the num-
ber of indices and floats. The first pair lists
adjacent input sites, the next d floats are the
normalized coefficients for the hyperplane, and the
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qhull(1) qhull(1)
last float is the offset. The hyperplane is ori-
ented toward verify that the hyperplanes are per-
pendicular bisectors. Use 'Fo' for unbounded
regions, and 'Fv' for the corresponding Voronoi
vertices.
FI Print facet identifiers.
Fm Print number of merges for each facet. At most 511
merges are reported for a facet. See 'PMn' for
printing the facets with the most merges.
Fn Print neighbors for each facet. The output starts
with the number of facets. Then each facet is
printed one per line. Each line is the number of
neighbors followed by an index for each neighbor.
The indices match the other facet output formats.
A negative index indicates an unprinted facet due
to printing only good facets ('Pg'). It is the
negation of the facet's id (option 'FI'). For
example, negative indices are used for facets "at
infinity" in the Delaunay triangulation.
FN Print vertex neighbors or coplanar facet for each
point. The first line is the number of points.
Then each point is printed, one per line. If the
point is coplanar, the line is "1" followed by the
facet's id. If the point is not a selected vertex,
the line is "0". Otherwise, each line is the num-
ber of neighbors followed by the corresponding
facet indices (see 'Fn').
Fo Print outer planes for each facet in the same for-
mat as 'n'. The outer plane is above all points.
Fo Print separating hyperplanes for unbounded, outer
regions of the Voronoi diagram. The first line is
the number of ridges. Then each hyperplane is
printed, one per line. A line starts with the num-
ber of indices and floats. The first pair lists
adjacent input sites, the next d floats are the
normalized coefficients for the hyperplane, and the
last float is the offset. The hyperplane is ori-
ented toward verify that the hyperplanes are per-
pendicular bisectors. Use 'Fi' for bounded
regions, and 'Fv' for the corresponding Voronoi
vertices.
FO List all options to stderr, including the default
values. Additional 'FO's are printed to stdout.
Fp Print points for halfspace intersections (option
'Hn,n,...'). Each intersection corresponds to a
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facet of the dual polytope. The "infinity" point
[-10.101,-10.101,...] indicates an unbounded
intersection.
FP For each coplanar point ('Qc') print the point id
of the nearest vertex, the point id, the facet id,
and the distance.
FQ Print command used for qhull and input.
Fs Print a summary. The first line consists of the
number of integers ("7"), followed by the dimen-
sion, the number of points, the number of vertices,
the number of facets, the number of vertices
selected for output, the number of facets selected
for output, the number of coplanar points selected
for output.
The second line consists of the number of reals
("2"), followed by the maxmimum offset to an outer
plane and and minimum offset to an inner plane.
Roundoff is included. Later versions of Qhull may
produce additional integers or reals.
FS Print the size of the hull. The first line con-
sists of the number of integers ("0"). The second
line consists of the number of reals ("2"), fol-
lowed by the total facet area, and the total vol-
ume. Later versions of Qhull may produce addi-
tional integers or reals.
The total volume measures the volume of the inter-
section of the halfspaces defined by each facet.
Both area and volume are approximations for non-
simplicial facets. See option 'Fa'.
Ft Print a triangulation with added points for non-
simplicial facets. The first line is the dimension
and the second line is the number of points and the
number of facets. The points follow, one per line,
then the facets follow as a list of point indices.
With option points include the point-at-infinity.
Fv Print vertices for each facet. The first line is
the number of facets. Then each facet is printed,
one per line. Each line is the number of vertices
followed by the corresponding point ids. Vertices
are listed in the order they were added to the hull
(the last one is first).
Fv Print all ridges of a Voronoi diagram. The first
line is the number of ridges. Then each ridge is
printed, one per line. A line starts with the num-
ber of indices. The first pair lists adjacent
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input sites, the remaining indices list Voronoi
vertices. Vertex '0' indicates the vertex-at-
infinity (i.e., an unbounded ray). In 3-d, the
vertices are listed in order. See 'Fi' and 'Fo'
for separating hyperplanes.
FV Print average vertex. The average vertex is a fea-
sible point for halfspace intersection.
Fx List extreme points (vertices) of the convex hull.
The first line is the number of points. The other
lines give the indices of the corresponding points.
The first point is '0'. In 2-d, the points occur
in counter-clockwise order; otherwise they occur in
input order. For Delaunay triangulations, 'Fx'
lists the extreme points of the input sites. The
points are unordered.
Geomview options
G Produce a file for viewing with Geomview. Without
other options, Qhull displays edges in 2-d, outer
planes in 3-d, and ridges in 4-d. A ridge can be
explicit or implicit. An explicit ridge is a dim-1
dimensional simplex between two facets. In 4-d,
the explicit ridges are triangles. When displaying
a ridge in 4-d, Qhull projects the ridge's vertices
to one of its facets' hyperplanes. Use 'Gh' to
project ridges to the intersection of both hyper-
planes.
Ga Display all input points as dots.
Gc Display the centrum for each facet in 3-d. The
centrum is defined by a green radius sitting on a
blue plane. The plane corresponds to the facet's
hyperplane. The radius is defined by 'C-n' or
'Cn'.
GDn Drop dimension n in 3-d or 4-d. The result is a
2-d or 3-d object.
Gh Display hyperplane intersections in 3-d and 4-d.
In 3-d, the intersection is a black line. It lies
on two neighboring hyperplanes (c.f., the blue
squares associated with centrums ('Gc')). In 4-d,
the ridges are projected to the intersection of
both hyperplanes.
Gi Display inner planes in 2-d and 3-d. The inner
plane of a facet is below all of its vertices. It
is parallel to the facet's hyperplane. The inner
plane's color is the opposite (1-r,1-g,1-b) of the
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outer plane. Its edges are determined by the ver-
tices.
Gn Do not display inner or outer planes. By default,
Geomview displays the precise plane (no merging) or
both inner and output planes (merging). Under
merging, Geomview does not display the inner plane
if the the difference between inner and outer is
too small.
Go Display outer planes in 2-d and 3-d. The outer
plane of a facet is above all input points. It is
parallel to the facet's hyperplane. Its color is
determined by the facet's normal, and its edges are
determined by the vertices.
Gp Display coplanar points and vertices as radii. A
radius defines a ball which corresponds to the
imprecision of the point. The imprecision is the
maximum of the roundoff error, the centrum radius,
and maxcoord * (1-An). It is at least 1/20'th of
the maximum coordinate, and ignores post-merging if
pre-merging is done.
Gr Display ridges in 3-d. A ridge connects the two
vertices that are shared by neighboring facets.
Ridges are always displayed in 4-d.
Gt A 3-d Delaunay triangulation looks like a convex
hull with interior facets. Option 'Gt' removes the
outside ridges to reveal the outermost facets. It
automatically sets options 'Gr' and 'GDn'.
Gv Display vertices as spheres. The radius of the
sphere corresponds to the imprecision of the data.
See 'Gp' for determining the radius.
Print options
PAn Only the n largest facets are marked good for
printing. Unless 'PG' is set, 'Pg' is automati-
cally set.
Pdk:n Drop facet from output if normal[k] <= n. The
option 'Pdk' uses the default value of 0 for n.
PDk:n Drop facet from output if normal[k] >= n. The
option 'PDk' uses the default value of 0 for n.
PFn Only facets with area at least 'n' are marked good
for printing. Unless 'PG' is set, 'Pg' is automat-
ically set.
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qhull(1) qhull(1)
Pg Print only good facets. A good facet is either
visible from a point (the 'QGn' option) or includes
a point (the 'QVn' option). It also meets the
requirements of 'Pdk' and 'PDk' options. Option
'Pg' is automatically set for options 'PAn' and
'PFn'.
PG Print neighbors of good facets.
PMn Only the n facets with the most merges are marked
good for printing. Unless 'PG' is set, 'Pg' is
automatically set.
Po Force output despite precision problems. The maxi-
mum outside distance is not determined
(qh_check_maxout). Verify ('Tv') does not check
coplanar points. Flipped facets are reported and
concave facets are counted. If 'Po' is used,
points are not partitioned into flipped facets and
a flipped facet is always visible to a point.
Also, if an error occurs before the completion of
Qhull and tracing is not active, 'Po' outputs a
neighborhood of the erroneous facets (if any).
Pp Do not report precision problems.
Qhull control options
Qbk:0Bk:0
Drop dimension k from the input points. This
allows the user to take convex hulls of sub-dimen-
sional objects. It happens before the Delaunay and
Voronoi transformation.
QbB Scale the input points to fit the unit cube. After
scaling, the lower bound will be -0.5 and the upper
bound +0.5 in all dimensions. For Delaunay and
Voronoi diagrams, scaling happens after projection
to the paraboloid. Under precise arithmetic, scal-
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