# Tracking moving points on a reconstructed plane

I would like to track animals moving on a plane from an aerial video. I'm very new to Blender, but believe that there is a way to do this. Up until now, I have managed to solve the camera motion from tracked points on the ground, and reconstructed the plane on which the animals are moving - this is set as the Floor of the scene, since it really is just a plane. Now I would like to track the animals - they are small in the footage, so every animal can be tracked by one marker.

My question is as follows: Can I tell somehow Blender that the animal object is located on the floor, and thus, can I solve its motion from only one track?

When you have a point that you have tracked in the Movie Clip Editor, you generally use it to solve camera motion. Occasionally, like in a VFX scenario, one might deploy a style called Two-point Motion Tracking. This uses two tracked points, reconstructed as empties that will move on an X/Y Plane. In the linked video, the narrator goes on to show that if you have a dowel rod with sharpie at the top and bottom (points for tracking), and you track those points, you can stretch a glowing cylinder between them and make it look like the person is wielding a lightsaber.

In your case, you will probably be looking at a type of One-point Motion Tracking, except with multiple one points for each scenario.

1. You will want to be happy with your camera track. After tracking the animals, re-solving the camera motion will be a pain to not possible.
2. Track an animal.
3. Go to Bottom toolbar > Reconstruction menu > Link Empty to Track. There should now be a Plain Axes Empty connected to the Camera by a dotted blue line.
4. In the 3D Viewport, switch to Local Transform Orientation.
5. Move the Empty as close or as far away from the camera as needed (probably along Local Z).
6. Parent your animal (I assume) to the Empty.

Hope this helps and happy Blending!

• It helped, thanks! :) Now the marker of the tracked animal appears on the 3D viewport, and moves more or less on the Floor plane. Is it possible to fix the Empty to the Floor, because I think that the distance between the Empty and Camera are fixed now, and - since the height of the camera changes slightly - the Empty goes sometimes below the plane and sometimes above a bit. – Katalin Ozogany Aug 17 '16 at 20:24
• @KatalinOzogany Glad to help! If you liked my answer, please consider accepting it by selecting the checkmark in its upper, left-hand corner. It would help me greatly and make me very happy! – Shady Puck Aug 17 '16 at 20:25
• Is it possible to fix the Empty to the Floor? The height of the camera changes slightly, and the Empty goes sometimes below the plane and sometimes above a bit, since the distance of the Empty and the Camera are fixed. – Katalin Ozogany Aug 17 '16 at 22:42
• @KatalinOzogany You could go to the Properties panel > Object Constraints tab > Follow Track constraint and click Constraint to F-Curve. Then, to to a frame in the Timeline where you like the Z-Axis Position of the empty in question. After that, key N to toggle open/close the 3D Viewport Properties Panel and go to the Transform tab. Right click on the Z: Location Field and choose Clear Single Keyframes. – Shady Puck Aug 17 '16 at 22:56
• @KatalinOzogany Glad to help! – Shady Puck Aug 18 '16 at 14:15