Mva Introduction

Introduction to Motion Video Analysis

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Introduction to Motion Video Analysis What is Motion Video Analysis? MVA is a software called Motion Video Analysis. It is developed by the Education and Manpower Bureau and the Department of Physics, The Chinese University of Hong Kong in 2004. User can use this software to capture the motion data of a moving object in a digital video clip. Motion graphs can be plotted and the exported data can use other software like Excel for further analysis. This software is mainly designed for students to explore and demonstrate the principles of mechanics in our reality.

Extract the zip file into a single folder.

Execute the MVA installer (filename MVA_setup.exe) to start the installation process and follow the procedure step by step. Restart the computer after the installation procedure is finished.

MVA user guide Start a new project. Execute the MVA.exe file to start the MVA software

Choose open video in the dialog box

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Introduction to Motion Video Analysis

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Choose the video file to be opened. Note: The video file format allowed are mpeg (.mpeg or .mpg) or avi (with the appropriate codec installed in the computer)

The file name, file type, frame rate, duration and pixel dimension of the video will be shown in the dialog box. You may preview the video by the play button. Specify the motion type to be analyzed. I.e., choose horizontal, vertical or 2 dimensional. In this example, we would like to analysis the vertical motion of a free falling ball shown in the video.

Click OK after choosing the type of motion.

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Introduction to Motion Video Analysis

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Input Reference Data In the dialog box, you are request to input the reference point. Click OK on the dialog box and click on a point on the video screen to specify where is the coordinate origin. The coordinate axes will be shown afterward.

Here, we take the initial position of the ball as the coordinates origin. A red coordinate axes are shown on the video screen.

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Introduction to Motion Video Analysis

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Then you are required to mark two points on the video to set the reference distance. Here, the two end points of the meter ruler shown in the video has 1 meter distance. So we click the two end point of the meter ruler. A yellow line joining the two marked points will appear. Enter 1 meter in the dialog box. And click OK. Note: you can click on any two points on the video screen which are separated by a known physical distance to serve as the reference distance.

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Introduction to Motion Video Analysis

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Input the mass of the object (i.e. ball) in Kg in the first box of the dialog box. The number of frame by which the video steps forward is 1. Click OK afterward.

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Introduction to Motion Video Analysis

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Setting Starting Frame and Ending Frame Users usually need to set the data starting and ending time of the video. Scan through different frames of the video by using scrollbar, move the video to the desired starting and ending frame and press the SET button of Starting Frame and Ending Frame accordingly.

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Click the Options button to open the Option dialog box. Click Show Axis and Show All Points. Click Apply button to display the axes and data points.

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Introduction to Motion Video Analysis

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Capture Motion Data Points on Video Click on the position of the moving object on the video screen in each frame step to input the motion data points. It will record the position of the moving object at different fimes. The time and coordinates of the motion data points will appear in the Point Data Panel. A set of displacement versus time data are obtained. Note: the Show Plot Panel button will only be available when all the motion data points within the starting and ending frame have been captured.

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Introduction to Motion Video Analysis

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Curve Fitting and Graph Plotting Using Plot Panel Pressing the activated Show Plot Panel button will the Plot Panel in a new window. Users can do polynomial fitting of the position data and plot motion graphs. As shown below, the Plot Panel shows the displacement-time graph obtained from the motion data. To do curve fitting for the displacement-time graph, first choose the No. of Sections to be fitted. Click on the No. of Sections pull down menu and choose 1, 2 or 3 sections to be fitted. For example, choosing 3 means the motion data are divided into 3 sets and each set can be fitted by a different polynomial in t.

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After choosing the No. of Sections, some Starting Points and End Points input boxes appear. These allow you to change the data point which mark the beginning and end of each section. In the case shown above, only one section is chosen and the total number of data point is 14, so the Starting Point and End Point are by default 0 and 12 respectively. The Fitting Method pull down menu allows you to choose how to fit the motion data, which may be either a linear, quadratic or cubic polynomial in t. Click on the Fitting Methods pull down menu and choose the type of polynomial fitting you want to do on the motion data. After inputting the No. of Section, the Starting Point and Ending Point for each section and the Fitting Method, press the Apply Fitting button. The Fitting Curve, which is the blue line on the displacement-time graph, and the Fitting Equation will appear. The pull down menus: Plot Velocity Graph, Plot Acceleration Graph and Plot Energy Graph will be activated and users can choose the graphs to be plot.

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Introduction to Motion Video Analysis

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To plot any of the Velocity Graphs, Acceleration Graphs or Energy Graphs, click on the Plot Velocity Graph, Plot Acceleration Graph or Plot Energy Graph pull down menus and choose the graph you want to plot.

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The velocity-time graph is plotted and shown below.

Note: you may use the Print Screen Key of keyboard to obtain the picture of the graphs. Choosing to plot other motion graphs will open new windows similar to the one as shown above.

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Save, Load and Export Functions The Export Data button and the Save Project button are located at the lower right corner of the window below.

The lower right corner of the above window is highlighted below.

Export Data The Export Data button export the motion data into a text file. Software like Excel can be used to analyze the motion data can be analyzed. Save Project Save the project before exit. The Save Project button saves the project information into two files, filename.mva and filename_setting.txt. Information about the motion data, curve fitting and graph plotting can be saved for later use. Note:The files of the project should be saved in the same folder so that it can be opened properly next time. i.e., the video file, the filename.mva file and the filename_setting.txt file of the project must be in the same folder. If you want to move the project files to 13

Introduction to Motion Video Analysis

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another folder or another computer, make sure that you keep all three files together in the same folder as shown below.

Load a Saved Project In order to load the previously saved project, press Open Project in the dialog box when MVA software is run at the beginning.

Choose the project file (filename.mva) to be openned and click OK

Modified from Source reference: MVAS [Copyright 2004 (c) EMB] http://www.hk-phy.org/mvas/

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