GAMGI Interfaces: Layer Modify

# Layer Modify

- Projection
- Position
- Visibility
- View

Change here the projection parameters of the layer (or list of layers, previously selected with Layer->Select, when Global is pressed). Parameters for empty entries or Local choices remain unchanged.

To change the layer name write the new name in the Layer entry, followed by the layer number (GAMGI only needs the number to identify the layer).

### Perspective, Orthographic

Change the type of projection of the layer. GAMGI projects the 3D space on the 2D screen using Perspective or Orthographic projections. The Perspective projection is better to simulate realistic views and gives users a depth feedback, but the Orthographic projection preserves object dimensions, as these are not distorted by perspective.

### Near, Far, Top

Change the dimensions of the space volume that is visible to the observer, after being projected into the window graphic area. This volume has six faces, and the front and back faces are always perpendicular to the viewing direction. Near and Far parameters set the distance from the view point to these front and back faces, respectively, corresponding to the minimum and maximum distances that the observer can see. Near must be smaller than Far.

In a Orthographic projection, the projection volume is a rectangular parallelepiped, so the 4 lateral faces are paralell and perpendicular to each other. In a Perspective projection, the projection volume is a truncated quandrangular pyramid, with the apex at the view point.

Top defines the half-height of the front face of the projection volume. The width is automatically determined from the ratio height / width of the window graphic area, so everytime users resize this window, the projection volume changes accordingly. Increasing Top increases the visible volume and decreases the size of the objects.

Each layer has its own projection 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.
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