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# Qhull print options (P)

This section lists the print options for Qhull. These options are indicated by 'P' followed by a letter. See Output, Geomview, and Format for other output options.

Copyright © 1995-2020 C.B. Barber

» Programs • Options • Output • Formats • Geomview • Print • Qhull • Precision • Trace • Functions (local)

## Print options

> Po
>   force output despite precision problems
> Po
>   if error, output neighborhood of facet
> Pp
>   do not report precision problems
>   Selection options
> PAn
>   print n largest facets by area
> Pdk:n
>   print facets with normal[k] >= n (default 0.0)
> PDk:n
>   print facets with normal[k] <= n
> PFn
>   print facets whose area is at least n
> Pg
>   print good facets only (needs 'QGn' or 'QVn')
> PG
>   print neighbors of good facets
> PMn
>   print n facets with most merges

### »PAn - keep n largest facets by area

The n largest facets are marked good for printing. This may be useful for approximating a hull. Unless 'PG' is set, 'Pg' is automatically set.

### »Pdk:n - print facet if normal[k] >= n

For a given output, print only those facets with normal[k] >= n and drop the others. For example, 'Pd0:0.5' prints facets with normal[0] >= 0.5 . The default value of n is zero. For example in 3-d, 'Pd0d1d2' prints facets in the positive octant.

If no facets match, use option 'Pg' to print the closest facet.

On Windows 95, do not combine multiple options. A 'd' is considered part of a number. For example, use 'Pd0:0.5 Pd1:0.5' instead of 'Pd0:0.5d1:0.5'.

### »PDk:n - print facet if normal[k] <= n

For a given output, print only those facets with normal[k] <= n and drop the others. For example, 'PD0:0.5' prints facets with normal[0] <= 0.5 . The default value of n is zero. For example in 3-d, 'PD0D1D2' displays facets in the negative octant.

If no facets match, use option 'Pg' to print the closest facet.

In 2-d, 'd G PD2' displays the Delaunay triangulation instead of the corresponding paraboloid.

Be careful of placing 'Dk' or 'dk' immediately after a real number. Some compilers treat the 'D' as a double precision exponent.

### »PFn - keep facets whose area is at least n

The facets with area at least n are marked good for printing. This may be useful for approximating a hull. Unless 'PG' is set, 'Pg' is automatically set.

### »Pg - print good facets

Qhull can mark facets as "good". This is used to

- mark the lower convex hull for Delaunay triangulations and Voronoi diagrams
- mark the facets that are visible from a point (option 'QGn')
- mark the facets that contain a point (option 'QVn').
- indicate facets with a large enough area (options 'PAn' and 'PFn')
- indicate facets with many merges (option 'PMn')

Option 'Pg' only prints good facets that also meet 'Pdk' and 'PDk' options. It is automatically set for options 'd', 'PAn', 'PFn', 'PMn', 'QGn', and 'QVn'.

### »PG - print neighbors of good facets

Option 'PG' can be used with or without option 'Pg' to print the neighbors of good facets. For example, options 'QGn' and 'QVn' print the horizon facets for point n.

### »PMn - keep n facets with most merges

The n facets with the most merges are marked good for printing. This may be useful for approximating a hull. Unless 'PG' is set, 'Pg' is automatically set.

Use option 'Fm' to print merges per facet.

### »Po - force output despite precision problems

Use options 'Po' and 'Q0' if you can not merge facets, triangulate the output ('Qt'), or joggle the input (QJ).

Option 'Po' can not force output when duplicate ridges or duplicate facets occur. It may produce erroneous results. For these reasons, merged facets, joggled input, or exact arithmetic are better.

If you need a simplicial Delaunay triangulation, use joggled input 'QJ' or triangulated output 'Ft'.

Option 'Po' may be used without 'Q0' to remove some steps from Qhull or to output the neighborhood of an error.

Option 'Po' may be used with option 'Q5') to skip qh_check_maxout (i.e., do not determine the maximum outside distance). This can save a significant amount of time.

If option 'Po' is used,

- most precision errors allow Qhull to continue.
- verify ('Tv') does not check coplanar points.
- points are not partitioned into flipped facets and a flipped facet is always visible to a point. This may delete flipped facets from the output.

### »Po - if error, output neighborhood of facet

If an error occurs before the completion of Qhull and tracing is not active, 'Po' outputs a neighborhood of the erroneous facets (if any). It uses the current output options.

See 'Po' - force output despite precision problems.

### »Pp - do not report precision problems

With option 'Pp', Qhull does not print statistics about precision problems, and it removes some of the warnings. It removes the narrow hull warning.

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Created: Sept. 25, 1995 --- Last modified: see top