Orthographic projection

[istan]

What is the math to define the FOV value for an orthographic projection?

I want to fit a certain size to the render output. e.g. 20mm should exactly fit to the width of the render window.

[Anonymous]

unless iam misunderstanding the question. Orthographic doesnt really have a FOV.

It just has dimensions of height and width.

If your thinking about making a camera view behave like a orthographic view then you need the camera super far away like almost infinately far away with really small FOV like.25 of a degree or somthing smaller. All depends on how much distortion you can tolerate but closer the camera the more distortion. The further away the more like an orthographic view but never a pure orthographic view.

[istan]

The 3dsMax orthographic camera uses FOV and "Target distance" for zooming. What I want to achieve is a geometrical correct rendering for later measurements. I.e. when I render to a 1000x1000 pixel image, one pixel shall have for instance 1mm or 0.5mm square size.

[Anonymous]

intended pixel square size X size of object your rendering (assuming its taking up full screen)

so an intended pixel size of .5 mm squares X width of your object say its 35 mm would  mean you want to render an image .5x35  = 17.5 pixel wide image
i think you would want to decide in advance what size each pixel would represent in advance and let that determine your render size. In my example the intended pixel size was probably to small

[istan]

Yes, somehow like that. Actually it makes the most sense for me, when I could specify the pixel size and define the render size depending on the scene data I have to export. Lets make an example: I need a resolution of 0.1mm and the object has an extent of about 50mm. Then I would set the render size to 600x600 (just to be on the safe side). Now I need to calculate the FOV and/or distance value for the camera..

[istan · Accepted solution]

this is the calc I was missing:
render_width = 2 * target_distance * tan( fov / 2 )

[Anonymous]

@istan Just made an Account to say many many thanks! You made my day so much easier :]

[istan]

you're welcome 😉