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--- wiki:motionscope_app2 [2022/05/18 12:19]
vizycam [Capturing non-parallel motion (homography to the rescue!)]
+++ wiki:motionscope_app2 [2022/05/18 15:52] (current)
vizycam [MotionScope]
@@ Line 8: / Line 8: @@
 {{wiki:motionscope3.mp4|816x540|loop,autoplay}}
+Check out the above video on [[https://youtu.be/z8bPvyXYJOw|YouTube]].
 ======Quickstart======
@@ Line 164: / Line 166: @@
 MotionScope provides plots of the motion data for easy visualization, but sometimes you want the raw numbers. At the bottom of the ''Analyze'' tab is the dropdown menu ''Export data''.
-{{wiki:image_865.jpg?250}}
+{{wiki:image_865.jpg?210}}
 Selecting one of these types will either download the data file or display it in a separate browser tab.
@@ Line 180: / Line 182: @@
 {{wiki:image_662.jpg}}
-For example, motion directed 45 degrees with respect to the wall won't be fully captured.  About 70% of the motion will be captured, 30% will be lost. (Cosine of 45 degrees is 0.7071 or ~70%.)  Many times we can't position Vizy such that its image plane is parallel to the motion.  For example, imagine capturing the motion of a ball falling from a building.  Here, we typically can only position the camera on the ground, so we necessarily need to point Vizy up at an angle (not parallel to the motion -- doh!)
+For example, motion directed 45 degrees with respect to the wall won't be fully captured.  About 70% of the motion will be captured, 30% will be lost. (Cosine of 45 degrees is 0.7071 or ~70%.)  Many times we can't position Vizy such that its image plane is parallel to the motion.  For example, imagine capturing the motion of a ball falling from a building.  Here, we typically can only position the camera on the ground, so in order to capture the motion, we necessarily need to point Vizy up at an angle (not parallel to the motion -- doh!  But we deal with this problem in the next section.)
@@ Line 193: / Line 195: @@
 These controls are fairly self-explanatory -- adjusting the controls changes the perspective of the live camera view.  The ''Shear'' controls are used less often, which is why they aren't normally displayed.
-Back to the "ball falling from a building" example, or in our case, ball falling from a parking garage: Vizy is pointed up at an angle to capture the motion of the ball as it falls.  Vizy is tilted 90 degrees to capture more of the vertical motion.
+Back to the "ball falling from a building" example, or in our case, ball falling from a parking garage: Vizy is pointed up at an angle to capture the motion of the ball as it falls.  Vizy is rotated 90 degrees to capture more of the vertical motion -- check out the picture of Vizy below (Vizy is on its side looking up).  Note also, it's hooked up to a [[wiki:powering_vizy#powering-vizy-through-the-usb-c-connector|portable charger for power]].
 {{wiki:image_908.jpg?360}}
 {{wiki:image_906.jpg?350}}
-We can adjust the perspective controls during analysis within the ''Analyze'' tab.  Note, how the sides of the parking garage become parallel -- it's as if we're looking at the plane of motion head-on instead of up at an angle.  Note also that we enable the ''Show grid'' overlay so we can line things up more easily (vertical lines should be parallel with respect to each other and the y axis.)
+We can adjust the perspective controls during analysis within the ''Analyze'' tab.  Note, how the sides of the parking garage stairwell become parallel -- it's as if we're looking at the plane of motion head-on instead of up at an angle.  Note also that we enable the ''Show grid'' overlay so we can line things up more easily (vertical lines should be parallel with respect to each other and the y axis.)
-{{wiki:perspective_2.mp4|800x450|loop,autoplay}}
+{{wiki:perspective3.mp4|800x450|loop,autoplay}}
-Before we adjust the perspective the ''x velocity'' graph is curved, but after the perspective is corrected, the ''y velocity'' graph becomes a straight line, which is what you'd expect from an object experiencing constant acceleration.  (Not to confuse things, but the ''x velocity'' graph becomes the ''y velocity graph'' after we rotate (roll) the perspective 90 degrees.)
+Before we adjust the perspective the ''x velocity'' graph is curved, but after the perspective is corrected, the ''y velocity'' graph becomes a straight line, which is what you'd expect from an object experiencing constant acceleration.  (Not to confuse things, but the ''x velocity'' graph essentially becomes the ''y velocity'' graph after we rotate (roll) the perspective 90 degrees, hoo boy, this was supposed to be a simple example...)
 {{wiki:image_922.jpg?350}}
@@ Line 209: / Line 211: @@
 By changing the camera perspective in this way, we are able to accurately measure the acceleration of the ball at close to 9.8 m/s<sup>2</sup>
-, although given the nature of acceleration (a derivative of a derivative) we need to average over lots of measurements to reduce the measurement noise -- below, we adjusted the ''Spacing'' so that we averaged over 17 measurement points to get the overall average acceleration.
+, although given the nature of acceleration (a double time-derivative of position) we need to average over lots of measurements to reduce the noise introduced by differentiation -- below, we adjusted the ''Spacing'' so that we averaged over all measurement points to get the overall average acceleration.
 {{wiki:image_923.jpg?350}}

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