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RW Background Won't Display


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A little help, please: with everything being equal in the two VPs shown in attached image, except perspective vs. orthogonal (front elevation) in the Projection setting (see screenshots of OIPs) why won't the RW Background (HDRI Sky...) display in the elevation view? It will display if Background render is set to OpenGL, but grays out using the Custom Renderworks Background Setting, which is exactly the same as the perspective view.

Screen Shot 2021-08-20 at 5.23.22 PM.jpg

Screen Shot 2021-08-20 at 5.26.15 PM.png

Screen Shot 2021-08-20 at 5.26.26 PM.png

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I do not know the answer for sure, but I believe you are seeing the HDRI background, just a very small portion of the sphere. This is typical in other software too when using HDRI backgrounds, which are essentially spherical backgrounds.  You can use a regular 2D rectilinear background for your orthographic views though.


So why does this happen... I believe this is due to the nature of orthographic projection.  The "camera" used in orthographic projection has a mathematically infinitely long lens value to depict edges without foreshortening / perspective effect, it's like the world's most powerful telephoto lense.  A perspective projection on the other hand uses a simulated real world lens length to calculate how the background looks.  So, when an orthographic camera calculates a curved HDRI background, it is infinitely far away and you end up seeing a single pixel of the HDRI background.  You can verify this by changing to different HDRI backgrounds and see the color changes.  All of this is an educated guess though based on how cameras in the real world behave.  The computer makes views using virtual cameras, so it stands to reason that orthographic projection interpreting spherical backgrounds could create a bit of a problem.

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Thanks, Jeff. I do believe you are right. I can use a 2D background in my RW-rendered Elevation views (see attached example, using a Google Earth image). Of course I wonder if this is explained anywhere in the KBase, or anywhere else easy to find? It sure would be good to know this without having to spend hours fruitlessly tinkering with settings! (Maybe I used the wrong search terms?)

Screen Shot 2021-08-23 at 7.54.36 PM.jpg

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