How do I match an orthographic type camera to an orthographic image?

Question

There's a program called fSpy in which you can draw lines on an image, and it will in turn give you a camera position and rotation, however it doesn't seem to work with orthographic images.

I have an image I want to recreate to scale, but it's in a trimetric view, I know all the angles to it, but it requires a lot of math to set up the camera and I don't think I'm able experienced enough to figure it out on my own. I tried eyeballing it, and while I can get close enough, I'd rather get it as close to perfection as I can. Is there some easy math algorithm or software feature that I can use to set up the camera? Thank you.

Answer 1

If you want to match a camera in orthographic view, to cover exact dimensions of an image – here's one way of doing it:

1. Add your picture as an image plane. TLDR: I recommend using Blender's stock addon, Images as Planes for that.
2. Make sure you have a camera in the scene and that it's attached to the render output. TLDR: If you have multiple cams, select your preferred one and press Ctr+NumPad0 to make it the render cam.
3. In Object Mode, select the image plane by clicking on it. TLDR: Marquee-select won't work for next step.
4. Press N to bring up the sidebar (aka N-panel) if it isn't open already.
5. Select the Item tab in the N-panel.
6. Under Dimensions properties, copy the highest value (X or Y). TLDR: N.B. To get exact sizes, click on the properties.
7. Click/select the Camera and refer to its Item tab in the N-panel. TLDR: Make sure to zero out any values in the X/Y/Z Location and Rotation properties.
8. Set Camera's Scale X/Y/Z to 1.
9. Now, in the Camera's Location Z property: paste the largest size that you copied from step 6. TLDR: Remove the trailing unit (m in my case) before pressing Enter. The Camera will move in position.
10. Open the Camera's Object Data Properties in the Properties editor.
11. Set Type to Orthographic if you haven't already, and paste in the same value you copied from step 6. TLDR: Minus the trailing unit (m in my case).
12. Open the Output panel in the Properties editor.
13. Under Resolution, enter the same dimensions as the image plane's (see step 6), but you'll want to raise the decimals upwards to a desired size.
14. In the 3D Viewport, press NumPad0 to see the Camera view.

Now the Camera should snugly fit around the exact same proportions as the image!