Engineering R&D Dr.-Ing. Alexander Gerhard
 
FAQ
 
FAQs.
You are welcome to send your
questions and suggestions via e-mail.
 
 
QUESTIONS
 
MovXact 2D Analysis
How do I measure distances?
How do I measure angles?
 
Mov3D 3D Analysis
Need the cameras be temporally synchronized?
 

General
Which markers shall I use in my test?
Where can I purchase self-adhesive markers?
Which video compressors shall I use? 
 
 
ANSWERS

How do I measure distances?
Would you like to show the relative displacement of a marker or the distance between two markers as a function of time? Or is your task defined as displacement of a marker between two time samples or as distance between two markers at a certain time value?
-> Please click here for a detailed answer (pdf, 76 KB)
 
How do I measure angles?
Would you like to show the angle of a marker or the relative angle between two markers as a function of time? Or is your task defined as angle of a line or as internal MXT angle at a certain time value? Or are you interested in the impact angle in a top view?
->
Please click here for a detailed answer (pdf, 174 KB)
 
Need the cameras be temporally synchronized?
Yes, definitely! In order to avoid spatial measuring uncertainty or errors during 3D triangulation, the point coordinates from the stereo views need to be defined at the same time sample. Therefore make sure that the used cameras have an identical trigger behavior and compensate any T0 delays. Also choose common exposure times of the cameras. Please note that for subsequent 3D analysis only identical recording rates make sense.
A time delay between T0 and the real start of the recording might lead to a strong influence in 2D analysis too.
Example:
Assuming an uncertainty of max. 1 ms (@ 1000 fps) and an impact velocity of 50 km/h, the measurement of the absolute displacement will show an error of about 14 mm!
 
Which markers shall I use in my test?
The markers as used should have high contrast and should be absolutely matt, not glossy. The physical size of the targets depends on the imaging geometry and the camera resolution.
All markers are free in scale! The internal measuring algorithms use a black-and-white extract of the color image, i.e. they do not use any color features to identify the markers.
->
Please click here for further details (pdf, 175 KB)
 
Where can I purchase self-adhesive markers?
The print shop Franz Maier (see Links) offers self-adhesive DOT and MXT markers in different sizes. Ask for special glue which sticks well on textiles and which is temperature-resistant. The glue must not affect the dummy skin.
 
Which video compressor shall I use?
The so far widely used codec (= encoder + decoder) Indeo Video 5.1x shows only restricted utilizability under Windows XP and Windows 7: a replay of videos in the Media Player via network is no more supported! 
Windows 7 offers instead the feature of playing files of MPEG4/ASP/AVC format without further installations of decoders. 
Therefore we recommend for FalCon eXtra the encoder x264.
->
Please click here for further details (pdf, 162 KB)
Hint:
For videos with charts or drawings, like diagrams with moving cursor, the Microsoft Video 1 codec is most suitable, because even thin lines do not show compression artefacts.
 
 
Fimstripe: Top View Car Crash
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Engineering Dr.-Ing. Alexander Gerhard · phone +49-89-28 44 44 · mail
info@dr-gerhard.de