Simulating PAPI/VASI lights

[renato.semadeni]

Hi there

 

We are currently implementing PAPI and VASI lights for our airports and we observe an interesting behavior of the light. We are using ObjectVolumesphere for the lights.

 

It seems as the lights get covered by the ground, when the camera's height increases. We observe that for around every 100m in the height, the light needs a z-axis offset around 5m. Otherwise it isn't visible anymore. Due to the geometry, we expect a small decrease of shining, but not as strong as we observe. Is this due to z-Buffer fighting?

 

Thanks for any help,

Renato

 

 

[sebastianbah]

Hi,

If you have light scattering enabled try to enable Post scattering option in Object Volume* material (Material window -> Common tab -> Post scattering).

 

For more specific advices, I'm afraid we need a simple test scene.

[renato.semadeni]

Hi there,

 

Thanks a lot for your reply. The post scattering is enabled, but what I found is that I have to set the polygon offset. So I suppose due to interpolating the ground model at farther distances, the light point get covered, right? Is the offset's unit in pixel?

 

Kind regards,

Renato

[sebastianbah]

Hi,

 

It's not totally clear, does the ObjectVolume located above Object Terrain or other object? Does it intersect with the ground of not?

 

Polygon offset can cause an inaccurate rendering of the intersection point, so it may be the cause of the visibility of volume object.

 

Also, if you need to lift the object depending on the distance from the camera, it would be better to use Word Expression object. It let you include such logic for a single object/group of objects.

[renato.semadeni]

Hi

 

Sorry, I try to explain our situation in more detail.

 

Our ObjectVolumeSphere is located slightly above Object ground and there are no other objects around. The poly offset is set to default, which means 0, I suppose. If we move now the camera horizontaly away, the light just gets smaller, but if we then increase the height of the camera the light disappears quite fast. Due to a spheric light model, we would expect that the resulting distance between light and camera defines if the light is seen or not. But the light is not acting this way. The height of the camera seems to affect the visibility of the light much stronger than the horizontal distance. I suppose now that the terrain gets simplified and therefore it covers the light.

 

I tried allready to lift the object with increasing vertical distance of the camera by means of expression. This is working so far but I have to lift the light up to 50m or so! The poly offset is set to default in this case.

 

My second approach was to change the poly offset. A polygon offset of 1 gives the same or even better results, without lifting the object.

 

Do you propose to lift the lights due to the camera vertical distance? This means every light calculates its z-position. What are the drawbacks using a small poly offset?

 

Thanks a lot,

Renato

[sebastianbah]

Hi,

 

I'm afraid, we can't reproduce such behavior, so it may be caused by your current terrain.

 

As for offset, it seems that there should be no problems with this solution.

[renato.semadeni]

Hi,

 

this is interesting, since we are using a migrated Washington scenery as base.

 

I attached some screen shots to the post.

 

Thanks for your help

Renato

[renato.semadeni]

And here a screen shot with poly offset 1 from high above.