Change here the volume parameters for a single layer or a list of layers.
To modify a layer, click over the graphic area to open a menu and choose a layer,
or write its identification (name and number) on the
Layer entry. To modify
a list of layers, press the button
List (after creating the list of layers
with
Layer->Select). Parameters for empty entries or
Local choices
remain unchanged.
To change a layer name write the new name in the
Layer entry,
followed by the layer number (GAMGI needs the number to identify the layer).
To change the name for a list of layers, press
List first
and then write the new common name in the
Name entry.
Eye
Change the user position, in the layer space. Any position in 3D space
is valid. Initially, the user is at (0, 0, +z), looking down to
(0, 0, 0), and the up direction is (0, 1, 0), so the x axis
points to the right, the y axis points to the top, and the z
axis points to the user.
Center
Change the position to where the user is looking. The distance from
Eye to
Center must be within the limits of visibility
(from
Near to
Far).
Up
Change the direction in layer space that points up, to the top of the
screen. This direction is converted internally to a unit vector
normal to the direction
Eye ->
Center, so any non-zero
vector that is not parallel to that direction is valid.
The user position and orientation can be defined by a (X,Y,Z)
layer referential, pointing from the middle of the screen to: the
right (X), the top (Y), the user (Z).
Eye is the origin,
Eye <-
Center defines the Z axis, and
Up
the Y axis, permiting to get the X axis by the cross product
of the other two axes. Initially, the axes are orientated along
(1,0,0) for X, (0,1,0) for Y and (0,0,1) for Z, but this is no
longer the case when the layer referential is rotated.
To move the user around the objects,
Eye,
Center
and
Up must change. A simple, interactive way to do this
is to press
Axes in the window toolbar and then either drag
the mouse or use the ruler, as described in
Introduction Mouse
and
Introduction Tools.
Each layer has its own position parameters, so in a window with
multiple visible layers, the image rendered in the graphic area
is the superposition of the various, totally independent, layer
views.