RTAREA(1)

NAME

rtarea - compute exposed and presented surface areas of geometry from a view

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SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO
AUTHOR
COPYRIGHT
BUG REPORTS

SYNOPSIS

rtarea [options] model.g [objects...]

The rtarea program uses librt(3) to ray trace the listed objects in the database model.g from a single view direction and reports the projected surface area of each region, each assembly (combination containing regions), and overall totals. The view is set with the -a (azimuth) and -e (elevation) options, or by feeding a model-to-view matrix on standard input with -M. All results are written to standard output as text.

If no objects are listed, rtarea uses the same automatic default-object selection described in rt(1). If no single usable default can be resolved, it aborts before computing areas.

Two areas are reported. The exposed area is the occluded 2D projection: what an observer would see if every object were opaque, so an object hidden behind another contributes only its visible fraction. The presented area is the unoccluded 2D projection: each region is considered in isolation and reports its full silhouette regardless of what lies in front. When totaling presented area for a group, area covered by more than one region is counted only once (the union of the regions), not the cumulative sum.

Only surfaces whose normal has a component facing back toward the ray are counted, so back faces are not reported as presented area.

Accuracy depends on the grid resolution: finer cell spacing (smaller -g/-G or larger -s) yields more accurate areas. Area centers are off by default and can be enabled with -c "set cc=1".

|----------------| rear region          |----------------| rear region
|                |                      |****************|
|        |--------------| front region  |****************-------| front region
|        |**************|               |***********************|
|--------|**************|               |--------|**************|
         |**************|                        |**************|
         |--------------|                        |--------------|

  exposed = presented area of front       exposed = presented area for groups
  region (fully visible)                  (e.g. comb of both visible regions)

|----------------| rear region          |----------------| rear region
|****************|                      |****************|
|********|--------------| front region  |****************-------| front region
|********|              |               |****************       |
|--------|              |               |--------|              |
         |              |                        |              |
         |--------------|                        |--------------|
  exposed area of rear                    presented area of rear
  region (partially occluded)             region (partically occluded)

Warning

The terminology and output format of rtarea may change in future releases.

OPTIONS

-a azimuth: Set the view azimuth in degrees and enable auto-sizing. Use with -e; conflicts with -M.
-e elevation: Set the view elevation in degrees and enable auto-sizing. Use with -a; conflicts with -M.
-M: Read a model-to-view transformation matrix (and optional animation script) from standard input instead of using -a/-e.
-s #: Set the square grid size to # rays on a side (default 512). More rays improve area accuracy.
-w #: Set the grid width in rays.
-n #: Set the grid height in rays (scanlines).
-g mm: Set the grid cell width in millimeters. If set without -G, cell height defaults to the same value (e.g. -g 25.4 gives 1 inch ray spacing).
-G mm: Set the grid cell height in millimeters.
-p deg: Set the perspective angle in degrees (0 ⇐ deg < 180; 0 is orthographic, the default).
-V [:]: Set the view aspect ratio width/height (e.g. 1.33 or 4:3).
-u units: Report areas in the named units (default mm). Use -u model for the database’s local units.
-U #: Set whether air-coded regions are retained (0 = discard, 1 = keep, the default for rtarea).
-P #: Set the maximum number of processor cores to use (negative = all but #).
-c command: Run an rt script command before ray tracing; may be repeated. rtarea recognizes set compute_centers= (or the alias set cc=) where 1 enables and 0 disables (default) computation and reporting of area centers.
-x #: Set librt debug flags as a hexadecimal bit vector (see raytrace.h).
-X #: Set rt program/optical debug flags as a hexadecimal bit vector.
-? or -h: Print a usage summary and exit.

EXAMPLES

Example 1. Areas of a group with centers, in inches

rtarea -u in -a 35 -e 25 -s 1024 -c "set cc=1" model.g all

Ray traces the group all in model.g from azimuth 35, elevation 25 degrees on a 1024x1024 grid, reporting exposed and presented areas in square inches along with the center of each area. Increasing the grid size and naming explicit units gives a more accurate, readable report than the defaults.

Example 2. Front-view area from a saved MGED view

rtarea -M model.g component < saveview.rt

Reuses the camera from an mged(1) saveview script (the matrix is read from standard input via -M) so the area of component is measured from exactly the view that was set up interactively.