&FIELD: angle


light

  When plotting 3-dimensional impressions, each panel of the
  solids is shaded in a more or less dark variant of its basic
  colour. Deliberately, a much simplified model, described below,
  has been chosen for the visualisation of 3-dimensional objects
  as many excellent programs for this purpose are on the market.

  A panel can become visible in two ways:
  - by reflection of light from the surface in the direction
    of the observer
  - by diffuse scattering of light at the surface

  Reflection is assumed to be perfect, light that is not reflected
  is assumed to be scattered - and it is assumed that losses can
  occur in the process.

  The darkness of the colour is therefore determined by the
  following factors:
  - the location of the light source, which can be set with the
    LIGHT-ORIGIN keyword followed by polar angle coordinates of
    the light source with respect to the viewing direction, by
    default 30 degrees in theta and in phi
  - the fraction of light that is reflected rather than scattered
    is set with the REFLECTED-FRACTION, by default 30 %
  - the fraction of scattered light that is not absorbed can be
    set with the SCATTERED-FRACTION keyword, by default 90 %

  Reflected light is assumed to be best visible when the normal
  vector of the panel is nearly equal to half the sum of the
  viewing direction and the light direction. A 1-sigma tolerance
  of 18 degrees is assumed for this process.

  A surface illuminated by scattering is assumed visible
  irrespective of the viewing angle, i.e. it is assumed that the
  outgoing light is fully random with respect to the incidence
  angle of the light. However, illumination is assumed to be
  strongest for nearly normal incidence with a 1-sigma tolerance
  of 60 degrees.

FULL-BOX-TICKMARKS

  Three dimensional impressions have the 3 backmost panels of
  the AREA as background, with a wire frame to indicate the 3
  coordinate axes.

  By default, only the coordinate axes on the periphery of these
  3 panels are shown so as to avoid ending up with an overcrowded
  plot, but you can obtain the 3 remaining axes by specifying the
  FULL-BOX-TICKMARKS option.

FULL-PLANES

  By default, the planes that are seen from the "inside" of the
  chamber are fully shown, while those seen from the "back" are
  merely outlined.

  On request, by specifying FULL-PLANES, the planes seen from the
  back will be shown fully,

  This option is meaningful only with 3D impressions.

FULL-TUBE

  By default, the parts of the tube that are seen from the
  "inside" of the chamber are fully shown, while those seen
  from the "back" are merely outlined.

  On request, by specifying FULL-TUBE, the parts seen from
  the back will be shown fully,

  This option is meaningful only with 3D impressions.

SPLIT-INTERSECTING-PLANES

  When plotting 3-dimensional impressions, an elaborate
  attempt is made to remove parts of solids that are hidden
  by others. Given the highly degenerate nature of some
  overlaps, this process can be very time consuming,
  in particular when many solids are present and when the
  solids intersect.

  Unfortunately, plots made with this option switched off
  are rarely meaningful. In a few rare cases, an acceptable
  result can be obtained with the SORT-PLANES option.

  The cutting procedure is complex and presumably still
  contains errors. Please contact the author in case of
  poor results and warnings from the PLASPL procedure.

  This option is meaningful only with 3D impressions.

SORT-PLANES

  As a slightly faster alternative to SPLIT-INTERSECTING-PLANES,
  one may request a sort of the panels.

  A panel that is partially hidden by another panel will be
  plotted first. There is however no order relation for hiding:
  if A hides part of B, and B hides part of C, then C can very
  well hide part of A. Hence, only very simple cases can be
  treated with this option.

  The main use of this option is to remedy cases where the
  SPLIT-INTERSECTING-PLANES procedure fails partially.

  The option is off by default.

OUTLINE

  Requests the outer edges of the solids to be emphasised with
  a line.

  Meaningful with 3D plots. Can also be used with CUT plots
  although, in this kind of diagram, the outer lines of the
  solids and the borders of the cut through the solids do not
  as a rule match.

  The lines are drawn according to the OUTLINE representation.

PLOT-MAP

  Requests the materials present in the field map to be shown.
  The option has no effect if the field is not taken from a
  field map.

  The materials are distinguished by their dielectric constant,
  which must therefore have been entered with the FIELD-MAP
  command. This can be done with an explicit map of dielectric
  constants, but also by a comparison of maps of E and D.

  Irrespective of the projection method (3D, CUT, X-Y etc), the
  materials are shown in the viewing plane - no attempt is made
  for instance to create a 3D impression.

  [This option is by default on if the dielectric constants are
  known.]

STEP

  Waits for a user response after plotting each panel of which at
  least part is visible. When the panel has been displayed, one can
  either simply hit return to proceed with the next panel, or type
  SHOW to see the coordinates, memory references and colour of the
  panel.

  Only active in 3D views.

  This is a debugging option.

  [This option is switched off initially.]

Keyword index. Formatted on 10/11/98.