What is the center of an HDRI environment map?

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#1

As an experiment in studying reflection using an HDRI environmental map. I encountered an expected behavior.

My object is a fixed sphere at world location 0,0,0. The camera is rotating around this sphere. But the animation gives the impression that the red sphere is moving. You can see the effect here.

Any clues, what happened.
Do I need to rotate the environment map instead? Including the sun light, which is the bright spot in the reflected clouds.

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#2

Hi,

This is interesting, I see what you tried to achieve here.

When you say that you are using an HDRI environmental map, do you mean you took an HDRI image to be the environment texture of the world’s background surface ?
World <This

If I recall right an HDRI picture is made by taking a 360° panoramic view at one place, so the center should be where the camera is. And that is the issue, it isn’t “physically” there. What I mean is, whenever you move the camera, the background’s center will move with it.

I picture it in my mind like so: You have a sphere with the background image projected on it, the camera is on the center of the sphere, you can rotate the camera to look up,down,left,right to see different part of that sphere, but when you translate the camera, the sphere translate with it.
What you can do to see what I mean is to go into camera view and move to the left or right and then rotate.

And you want the background to actually be centered on the sphere, right ?
Given that, it would be quite tricky to achieve what you are trying to do, won’t it ?

:thinking: Or … would it ?

The only way I see to cheat a little is to:

  1. Create a sphere centered on 0,0,0;
  2. Scale it by 100 or so to actually be inside it;
  3. Project the HDRI image on it (it may be tricky given the shape of the projection), be sure to flip normals;
  4. Apply an emissive material to recreate the natural lighting with the HDRI image on color factor;
  5. ???
  6. Profit :slight_smile:

Or maybe you did something else ? And already figured it out ?

I hope this will help.

Cheers !

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#3

Is your camera tracking set up properly? If the sphere is at 0,0,0 then it should not stay in the centre of the view, it would move the opposite way to the camera.

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