Spot light on off
Function Name(s) :
SPOT LIGHT ON
This function allows you to artificially illuminate the data displayed on the screen with a camera relative light. Surface rendering and shading will be applied to triobjects (DTMs) which have been drawn and strings which have been drawn as polygons. This adds another level of complexity to the viewing system and can add some time to the process of re-displaying a new view but the result achieved is generally worth it.
The camera relative light that is inserted into the scene always shines from the camera location (your eye point) towards the target (the viewing point) regardless of how the scene or rotated or scaled. This provides consistent illumination without the dimming effect created by the lights provided by the LIGHT ON function whose lights always shine from the same absolute direction.
The colour of the camera relative spot light and the illumination code can be controlled to achieve specific lighting effects.
Illumination code (degrees)
The width of the illumination cone can be defined as a number of degrees of arc. The illumination cone may be any value greater than 0 and less than 180. A cone of 180 degrees of arc will illuminate everything in front of the camera. Small values for the illumination cone will provide a tightly focussed light that only shines on a portion of the scene.
Sharpness cone (degrees)
The sharpness cone defines a ring inside the illumination cone inside which the light is at full intensity. Note that the value for the sharpness cone must be equal to or less than that of the illumination cone.
The light intensity reduces linearly between the extent of the sharpness cone (at full intensity) to the extent of the illumination cone where it is at zero intensity.
Spot light colour
Define the colour for the light source. Colour names may be simple names, for example `red', `green', `blue' or complex names, for example `light green', `dark red', `greenish blue'.
Offset angle from camera->target (degrees)
The spot light is a camera relative light that shines directly from the camera position towards the target position. On surfaces that are predominately flat this can cause excessive glare when in plan view. This offset angle causes the camera to be offset from the camera position by an amount that is dependent upon the distance between the camera and target positions. The effect will be the same regardless of the scale of the data.
Often a small offset angle will give superior results by reducing the glare.
Rendering method
Any objects which have been drawn using the DRAW SHELLS function will respond to different types of lighting interpolation. Lighting interpolation is an advanced rendering option which enhances the presentation of images.
The available choices are:
- None - No lighting interpolation. The colour of a triangle face is fixed for the entire triangle face.
- Gouraud - Gouraud shading. This is a technique which is used to vary the colour across the triangle faces. This is done by determining the colour at each vertex and then interpolating this colour across the triangle.
- Phong - Phong shading. This is a technique similar to Gouraud shading which is used to vary the colour across the triangle faces. It generally gives more realistic results at the expense of increased processing time.
Both Gouraud and Phong shading tend to smooth the rough edges from objects and give a far superior graphic presentation of the data. Often Gouraud shading is implemented in hardware thus making it even faster than Phong.
Edge Lighting
Any objects which have been drawn using the DRAW SHELLS function can have lighting applied to just the faces or to both the faces and edges.
Result
If the picture contains polygons or triobjects (DTMs) and the faces are visible then the view will alter to show the surface shading effects of the defined illumination sources.
SPOT LIGHT OFF
Function: SPOT LIGHT OFF
Illumination provided by the spot light is turned off and the display will alter accordingly.