&FIELD: angle
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.
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.
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.
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.
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.
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.
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.
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.]
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.