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Thank you for your info.

Rotating the environment light indeed changes the orientation of HDRI image. I don't know why this method was not effective at that time.

I also find a way to interactively manipulate HDRI not only the orientation, but also HSV and other effects as long as you can do in COP.

First, in the obj that you want to use HDRI (say for chrome effect),
make a COP. Use File node to import the HDRI and add a transform node.

To change the orientation of HDRI, in transform node, set Image Wrap to “Repeat”. By changing the “tx”, you can change the orientation of HDRI.

Finally put a null node at the end of the COP node tree.

Second, in Environment Light node, type “opbj/OBJ_NAME/COP_NAME/NULL_NAME” in Area Map Parameter.

Apply material (say chrome) to obj.

Now, with Render View, you can interactively change the orientation and other features by tweaking parameters in obj's COP.

I tried to make the same COP network in SHOP material and use the envmap VEX node linking to COP (in material) with “op: MATERIAL_Name/COP_NAME/NULL_NAME” but with no success.

If making COP in SHOP Material and use the “op:” to link envmap VEX node to COP node is feasible, it may be a lot easier applying to obj.

This is my first post on Houdini forum, quite exciting.

I started learning Houdini from last December. Before that I took one-week lesson on Maya in 2007, but then never touch any 3D apps again until last Dec. So I think I can say that Houdini is my first real 3D application experience, and it is very interesting learning Houdini.

I made a HDRI test, and this is the result:
http://www.vimeo.com/10496215 [vimeo.com]

I have three questions, and hope someone can kindly give me some suggestions:

Question 1: I can't figure out how to change the orientation of the environment map in chrome material.

Actually the reddish light should come from right side and the blueish from left side.

Using chrome material for torus, I noticed that in Surface Tab -> Reflections Tab -> Environment Map Tab, there is an “Env Map Space”.
After trying to change it to “Use Other Object” and create a null in Scene, there is no reaction when altering the rotation value of the null object.

Using environment light node was tried, but changing the rotation value of environment light doesn't change anything.

I also tried to use light template with VEX Global Illumination node in SHOP. In Irradiance Tab, there is a Null Object operator chooser. I tried to link to the null I created in Scene and there is no reaction as I adjusting the rotation of the null.

Is there anything I did wrong? or I have to change panoramic HDRI orientation instead of adjusting it afterward in Houdini?

Question 2: The reflection pass is strange and not correct.
I guess there maybe some relation with environment light orientation but not very sure.

Question 3: The shadow of the leftmost torus is strange at the moment it fell on the table and stop moving. It looks like the shadow suddenly disappeared. I totally have no idea if it's correct or not, but it looks strange to me.

This is my HDRI workflow:
1. The mirror ball you see in the video is used.
2. After panoramic HDRI was made, it was converted to cube map (vertical cross) using HDRShop.
3. The .hdr cube map was converted to .rat format using isixpack.

Thanks for any suggestions.

p.s. I use Mac Pro (Early 2008), Mac OS 10.5.8