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Positioning BGL lights

T

trfsd

Messages
149
Starting with the excellent PAPI tutorial, I have successfully created VASI, REIL, and MIRL lighting using BGL lights. That said, I have been struggling to properly position the light balls relative to nearby scenery objects.

In the PAPI tutorial, the BGL lights are positioned using small boxes in front of the model of the PAPI lighting box. I am using essentially the same approach for my VASI light boxes. When I slew the plane backwards away from the VASI box, however, the light ball appears to move leftward and upward relative to the visible model of the VASI box.

My observations lead me to believe that the position of a BGL NAV light in XYZ space is not centered in the middle of the bitmap that represents the light ball. Also, when you back away from the light, the light ball stays roughly the same size on screen while the background model shrinks. Since the light ball bitmap is not centered on its position in 3D space, it appears to shift up and to the left relative to the shrinking VASI box.

The consequence of this is that I cannot position the BGL light relative to the visible model of the lighting fixture in a way that looks right at all distances. Am I missing some critical step here, or is this a known bug for which there is no complete solution?

Taylor
 
Hi Taylor,

The size of the light is indeed changed by the engine, depending on your distance. So the light seems to grow a bit.

For the positioning problem, I must say I did not mention it before myself. I assume you are aware that it is the centre of your reference object in GMax that determines the position of the light?
 
Yes, I know that the position of the light is based on the center of the reference object in gmax. But no amount of moving that point around will change the basic behavior of the light. When you slew backwards, the light appears to move up and to the left relative to any nearby visible objects.
 
I finally figured out what was going on with the movement of my lights. I have ActiveSky 6.5 installed. ActiveSky Graphics replaces many textures, including halo.bmp. It turns out that 3 out of the 5 versions of halo.bmp that ship with ASG are very poorly aligned with the center of the light. So the reason that my lights appear to shift up and to the left when I back away is that most of the ASG versions of halo.bmp have the light ball in the wrong spot. Versions 4 and 4b that come with ASG work just fine. But versions 1,2, and 3 are a real problem. I have now locked in version 4 as my choice of halo.bmp in ASG, and all is well again.

Now I just need to go back and reposition my lights in gmax to properly center them on my VASI box model.

Taylor
 
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