I think it is OK, as long as it is a part of the setup. I like to think about the Match Photo process as reverse-engineering the spot from where the camera was when the shot was taken. Not only that, but the perspective lines allow for the focal length of the lens to be reverse engineered. While it is not necessarily procedural in that things need to happen in a certain order, I like to use the grid as the last step to reverse engineer the scale. After a few pieces are modeled, a ceiling height for example, I then use the model itself rather than the grid to match the scale of the photo to my virtual 3D environment. The photo is never really scaled, just the world and view relative to it.
Two potential issues to be aware of are this: If you scale (or move) the model after, and then return to the MP scene, it will no longer align to the imported MP photo. I used to skip the grid-aligning step and just use the measure tool to scale a known length. That is a bad practice, unless you absolutely no longer need the imported MP photo and it’s scene. The other thing to consider is that if the grid is moved while in MP edit mode, any textures projected from the image will remain from the view that they were projected from.
Think of it as comparing two camera locations, one in the real world and one in the virtual world. Moving perspective grid lines, axes locations (yellow box) and grid lines in the MP edit mode is really just moving the virtual world camera location to a spot that may or may not be closer to the relative position of the real world camera that took the photo.
- matt