Mostly photos - 3D modelling the photoshop way ...

Lately I am trying to work out a nice way to shape a common estate, lying between our neighbourhood's houses.

So, I have to find out, how the rest would look like if we placed some trees or bushes there.
For now, I've played around with Gimp and some planes and fitted images of trees there in the right proportions...

That is exactly the tricky bit - knowing, how big a tree was according to its position and thereby its distance.
The easiest way would be to have a good 3D image with the right scale.
.... soooo .... let's get one.

The task ahead is to get this image as easy as possible with the least amount of equipment.
Smartphones are omnipresent and have quite some processing power, so it would be a shame, if you needed much more.

Problems and solutions

To get a 3D image you just have to make two photos of the same scene from slightly different perspectives.
To get the scale right (without knowing anything further) you would have to know quite much about the camera's lens system and configuration.
A much easier way is to place two folding rules into the scenery before you take the photos.

The right way to get the shift and direction between the photos right would be to use a tripod and some special gears for the linear shift.
A much easier way is to use the G-sensors and hope that an integration of the movements leads to the right position etc.

To get a real 3D image, the underlying images would have to be rectified. Another time .... knowing the lenses well enough to cope with their faults.
A much easier way is to see how it fails... Taking to pictures from the same position but with slightly different directions...
If the lens has no fish eye whatsoever, the pictures would be the same apart from a shift to the right for example... But you will have a fish eye and you (or the software) will have a hard time finding the corresponding pixels.

The rectification of the camera lenses can be done in a preliminary step and it would be strange if such an application/library wasn't already available...

And then ...?

You would only have to provide a good library of scaled and cropped images, you can blend in as an overlay...