Link Light intensity to Camera Position

[Dan Ebberts]

It’s hard to picture exactly how you have things set up, but would it make sense to have the light dim when the angle formed by the camera, earth center null, and the light is greater than 90 degrees? Also, over what range should it dim (I mean, it doesn’t just turn off as soon as it crosses the threshold, right?)

Dan

[Ben Mason]

Thanks for getting back to me Dan, much appreciated.
That sounds like a very clever solution – hadn’t thought of that
re: set up
Here is a still

I plan to cut between multiple camera angles of the earth, which is why I am keen to have a solution that doesn’t involve keyframing multiple lights on and off for each shot.

Set up is…
Element 3D sphere – linked to master null for rotation, position, scale
Parented to that master null are 20 city location nulls (positioned and aligned to the earth’s surface)
Also parented to that master null are 20 lights, with same position data as each of the city nulls
Each light represents as a flare courtesy of Optical Flares
Problem is that lights on the far side of the planet show up on this side.
So I thought that if they reached the horizon line of the earth I could reduce the light’s intensity and they would effectively fade out before they cross the horizon line.
I found an expression for reducing a layer’s opacity based on distance from camera but this requires an anchor point for the layer and lights don’t have one? It’s in the box below


start = thisComp.layer("Control").effect("FadeStart")("Slider");

end = thisComp.layer("Control").effect("FadeEnd")("Slider");

CameraPos = thisComp.activeCamera.toWorld([0,0,0]);

LayerPos = toWorld(anchorPoint);

Difference = length(CameraPos, LayerPos);

linear(Difference, start, end,0,100);

Ben Mason
motionographer
London
UK

[Dan Ebberts]

For lights and cameras, just use [0,0,0] instead of anchorPoint.

Dan

[Dan Ebberts]

If you wanted to try the 90 degree angle thing, you could set it up like this:

thisComp.activeCamera.toWorld([0,0,0]);
LayerPos = toWorld([0,0,0]);
earthNull = thisComp.layer(“Earth Null”);
EarthPos = earthNull.toWorld(earthNull.anchorPoint);
v1 = CameraPos – EarthPos;
v2 = LayerPos – EarthPos;
angle = radiansToDegrees(Math.acos(dot(normalize(v1),normalize(v2))));
linear(angle,85,95,100,0)

(it assumes there’s a layer named “Earth Null” at the center of the earth). Adjust the last line to change the angle range where the fade occurs.

Dan

[Dan Ebberts]

Ooops… I messed up the first line. Should be like this:

CameraPos = thisComp.activeCamera.toWorld([0,0,0]);
LayerPos = toWorld([0,0,0]);
earthNull = thisComp.layer(“Earth Null”);
EarthPos = earthNull.toWorld(earthNull.anchorPoint);
v1 = CameraPos – EarthPos;
v2 = LayerPos – EarthPos;
angle = radiansToDegrees(Math.acos(dot(normalize(v1),normalize(v2))));
linear(angle,85,95,100,0)

Dan

[Ben Mason]

Thank you Dan, looks great – really appreciate you looking at this!

Do you mind if I get back to you tomorrow afternoon if I have any queries?
Currently on another project deadline for tomorrow.

Ben Mason
motionographer
London
UK

[Dan Ebberts]

Not a problem. Fire away.

Dan

[Ben Mason]

Hi Dan,

So I’ve renamed the main null as ‘Earth Null’ and applied the expression to one of the lights – is that correct? do I need to do anything else?

I’m getting an odd error message

any thoughts?

Ben Mason
motionographer
London
UK

[Dan Ebberts]

Sometimes expressions will break because the active camera is undefined at times before zero. See if either of these help:


if (time >= 0){
CameraPos = thisComp.activeCamera.toWorld([0,0,0]);
LayerPos = toWorld([0,0,0]);
earthNull = thisComp.layer("Earth Null");
EarthPos = earthNull.toWorld(earthNull.anchorPoint);
v1 = CameraPos - EarthPos;
v2 = LayerPos - EarthPos;
angle = radiansToDegrees(Math.acos(dot(normalize(v1),normalize(v2))));
linear(angle,85,95,100,0);
}else{
value;
}



try{
CameraPos = thisComp.activeCamera.toWorld([0,0,0]);
LayerPos = toWorld([0,0,0]);
earthNull = thisComp.layer("Earth Null");
EarthPos = earthNull.toWorld(earthNull.anchorPoint);
v1 = CameraPos - EarthPos;
v2 = LayerPos - EarthPos;
angle = radiansToDegrees(Math.acos(dot(normalize(v1),normalize(v2))));
linear(angle,85,95,100,0);
}catch(e){
value;
}


Dan

[Kalleheikki Kannisto]

As an alternate solution you can use a lightmap on a (hidden) duplicate layer of the Element 3D sphere as the source for Optical Flares. The lightmap is a texture that has white dots where you want light sources and otherwise black. With recent AE versions you can use the result directly or in earlier version you need to precompose with a linked camera. Use “Luminance” as source type in Optical flares and select the lighmap E3D layer. No expressions required with this method.

Kalleheikki Kannisto
Senior Graphic Designer