Approximate billboard scale give distance from camera when scaleByDistance is set

CesiumJS
1

Hello,

How can I calculate by what scale a billboard is getting reduced at a given distance from camera when scaleByDistance is set? I am trying to calculate if some billboards are over lapping in the current camera view. I have scaleByDistance set at NearFarScalar(1.0e6, 1.0, 5.0e7, 0.0) and I am trying to find out by what factor I should reduce width/height of a billboard to calculate the space it is occupying in the current view.

Thanks,

Tim

2

Hello Tim,

> How can I calculate by what scale a billboard is getting reduced at a
> given distance from camera when scaleByDistance is set? I am trying to
> calculate if some billboards are over lapping in the current camera
> view. I have scaleByDistance set at NearFarScalar(1.0e6, 1.0, 5.0e7,
> 0.0) and I am trying to find out by what factor I should reduce
> width/height of a billboard to calculate the space it is occupying in
> the current view.

the scale change is non-linear and calculated as:

  t = [(distance^2 - near^2)/(far^2 - near^2)]^0.2
  t = clamp(t, 0, 1);
  
  scale = nearValue*(1.0-t) + farValue*t;

See
  Source/Shaders/BuiltIn/Functions/nearFarScalar.glsl

for the details.

Manuel

3

Thanks Manuel!