9 Replies Latest reply on Mar 29, 2011 11:58 PM by Mylenium

    Scientific Motion Tracking?

    djdadi

      Hi all,

      Is it possible to use the motion tracking feature to track a point in a time lapse and "draw" the tracked point's path to be used in scientific research?  Or even better is there a way to measure a distance of drawn particles or angle's of the lines created?

       

      I know there are many software packages out just for this type of stuff (ImagePro), but we don't have those packages readily available at my university.

       

      Thanks!

        • 1. Re: Scientific Motion Tracking?
          Dave LaRonde Level 6

          I can think of a way to do it, but it's not very scientific.

          • Create a comp and a solid that have the same horizontal & vertical dimensions and pixel aspect ratio as the footage to be tracked.
          • Create a null object.
          • Add the footage and do the track.
          • Apply the track to the null object.
          • Create a simple mask path on the solid, and make a mask shape keyframe for it.
          • Copy the null's position keyframes, and paste them into the solid's keyframe
          • Use the Stroke effect to create the line

          I've never done it personally, but it ought to work.  You may have to play around with the duration of the solid's mask shape keyframes, but you can do that.

          • 2. Re: Scientific Motion Tracking?
            Mylenium Most Valuable Participant

            Visualizing a track is easy a proverbial pie - simply emit a particle every frame and let it live forever. Even AE's Particle Playground can do that with a cannon. Plotting and analyzing values would be possible by ways of expressions which, depending on the situation, could be simple or infinitely complex... You'd have to be more specific about that.

             

            Mylenium

            • 3. Re: Scientific Motion Tracking?
              djdadi Level 1

              Thanks guys that seems easy enough trace a tracked point.  As for the analyzing, it would be fairly simple, such as change in verticle distance or change in angle between a fixed point and the point being tracked.  I'm not very experienced with AE, where do you enter these expressions?

               

              Thanks

              • 4. Re: Scientific Motion Tracking?
                Dave LaRonde Level 6

                If you need to return precise measurements, you'll have to devise a Plan B. 

                 

                AE only nows about pixels.  Meters and millimeters are beyond its comprehension.

                • 5. Re: Scientific Motion Tracking?
                  djdadi Level 1

                  That shouldnt be too much of a problem, I can come up with a conversion of pixels to meters easily enough.  I would love to have a plan B and use other softwares made for this, but it seems like all of them cost thousands.

                  • 6. Re: Scientific Motion Tracking?
                    Dave LaRonde Level 6

                    djdadi wrote:

                    That shouldnt be too much of a problem, I can come up with a conversion of pixels to meters easily enough.

                     

                    I hope you're right, but personally, I don't see a practical way to do it.  If you find a way, write back.

                     

                    I easily see situations arising where you move the camera and use the zoom lens, and suddenly a pixel is a much different measurement.

                    • 7. Re: Scientific Motion Tracking?
                      djdadi Level 1

                      The camera won't be moving during a time-lapse, or zooming.  It will be similar to this video, except a higher frame rate, and more focused on one plant (and possibly one leaf). 

                       

                      http://www.youtube.com/watch?v=qCtE8nCKG1A

                      • 8. Re: Scientific Motion Tracking?
                        Rick Gerard Adobe Community Professional & MVP

                        You need to put something of a known length into the frame. It could be anything. If you place the item at the same distance from the camera then accurate measurements can be taken. If you have a point of reference you can also load rendered frames into Photoshop Extended and use the measurement tools there. Measurements can also be used in the Vanishing Point plug-in in Photoshop.

                         

                        If you don't want a reference item in the shot just put a ruler in the frame for the first few seconds, then pull it out. Measurements can then be made using the first frame as a reference. You could even note the focal length of the camera and the focus distance, then establish some numbers using rulers. This would give you a basis for measurements that could be translated to any shot.

                        • 9. Re: Scientific Motion Tracking?
                          Mylenium Most Valuable Participant
                          where do you enter these expressions?

                           

                          Expressions can be applied to any animatable property, i.e. anything that has a stopwatch. Check the help on teh topic. As for the rest I agree with Rick - you will need a reference measure if this is required to be expressed in realworld units. However, zooming or changing camera POV doesn't go down well with such stuff - a 5cm reference scale will just be a bunch of mooshy pixels when zoomed out too far, considerably skewing the results of any measures taken from that zoomed out picture. A better strategy generally is to use as high-res a camera as possible with a static zoom factor and properly aligned to the reference scale.

                           

                          Mylenium