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Mapped sphere 球天贴hdr的方式 http://bbs.hxsd.com.cn/showthread.php?t=9824396

For the most control it is best to map the HDR image onto the inside of a large flipped sphere that surrounds your scene. Create a sphere that surrounds your scene, next add a Normal modifier and check the Flip Normals option.

很多时候用球天来控制hdr贴图是个好办法。 创建球天的方法：建立一个大的sphere 来包裹注你的场景，给它一个法线修改，让贴图在球的内部显示出来。

Lastly add a UVW map modifier and choose the correct mapping type (see above).
增加一个uvw map修改，选择正确的贴图形式。

From fR-Properties make sure that the sphere is Sending GI, you can turn off send/receive shadows and also receive GI/Caustics as these are not needed.

从右键Object Properties属性面板（新版fr已经把fr-properties集成到了max的propties面板内部），设置球体发射光子，也可以关闭或者打开阴影生成，打开或者关闭焦散生成（如果不需要焦散效果）。

Next create an fR-Advanced material and apply the HDRI to the self-illumination slot. Apply this material to your sphere. By using an fR-Advanced material - you can tweak the Send GI multiplier as well as the HDR exposure amount.
最后创建一个 fR-Adanced 材质，把hdri（hdr图片）放置到自发光栏。将此材质赋予球天。通过控制材质，来掌控GI的发射和hdr的曝光度。

Note: Depending on the relative scales of the sphere to your scene you may need to use local GI settings on the sphere to avoid artefacts, do this from the fR-Properties menu if necessary.
注意：某些地方你需要控制局部参数来消除球天带来的人为的负面效果。

Once set-up I usually freeze the sphere and forget about it.
通常我把这个球天冻结，然后很少去关注它。
Pros: Full control of how much light is emitted. Full control over map rotation/placement. Full control over visibility to camera, reflections, refractions, etc.

优势：很方便控制光线的发射，也容易控制天空的方位，对所有产生效果的元素可见。

Cons: Additional geometry to deal with. Possible need to use local GI properties.
劣势：增加了几何体，需要控制局部的GI参数来消除影响。