# How to place a 3d object in a photo with correct measurements?

I want to make a Infographic, which shows how much water is flowing down a river per sec.

To do this I want to make a photo near the river and place the amount of water with imaginary 1m³ bricks.

But that infographic only works when the size of the bricks are correct to the scale of the image.

How do I do this, or what is the correct research term for this?

I imagine something like importing the image into a 3d program and add a two point perspective to the image? And then place the bricks within that perspective grid based on a 1m ruler I've put on the photograph?

• Yes well, several complications. One a 1 image shot does not work it gives no clues for 3d unless you have lots of straight lines even then its a wild guess. Your better of having several pictures to track from. Second camera tracking procducs a scaleless solution that is a camera works the same if the subject is near or far (well ok for a non ideal camera physical blur is dependent on the hole size), so you need something in the image you know the scale of to pinpoint the scale. See: ssontech.com/learning.htm Jul 27, 2014 at 21:32

I think you could do this placing a few guides on your image.

Since it is an outside scene, you should be able to get realistic results using a simple one-point perspective.

Photoshop has a Filter called `Vanishing Point` that can help you a lot.
There is also `Edit > Transform > Perspective`, but any free-transform tools should work for you.

The most important thing is to get some measurements of objects that are in the scene for reference. These could be:

• Road width or River span
• Benches, trashcans or any other objects you know the dimensions of
• Placing a large object into the picture like a 1x1m cardboard or measuring tape extended to a certain length. Ideally both

I think you'll get the best results taking 2 or more photos with a tripod.
The first photo is the one you'll use for your final image. The second photo has to be taken from the same perspective (hence the tripod) with anything that marks the size and position of the base of the brick like cardboard, paper, etc. The most important one is the brick closest to your camera!
If your brick is too large for one cardboard or paper you could place markers in each corner like sticks, pencils, anything bright or easily distinguishable from the ground and then take the second photo.

The Photoshop "Vanishing Point" filter is very convenient, since you can draw your first brick where you placed the marks in the photo and then, using the filter, you can clone the rest as deep and high as you need.
Otherwise you'd need to draw a grid based on the reference markers of your second photo to get the perspective right

I hope this gets you started!

• Thanks for your hints. I never used that vanishing-point in photoshop. I guess I should look into it.
– KSPR
Jul 29, 2014 at 7:34

You just need a point of reference. For example a trick for interior is using a doorway.

Your image is an outdoor shot, so it will be harder to use a reference, however, there is a way.

Since you're making this infographic, you must have the data. Therefore you can work backwards. If you know that the amount of water from you data is say 200m³ then you know you need to design the cube shapes to be 1/200 the size of the area they will fit.

(I believe FAR more water than this flows through most rivers if using a per second volume)