*ObjectR Basic – Tripwire

Technical Article | TA-20201002-TP-12

VDG Sense | Video Content Analyses | ObjectR Basic

Note: ObjectR Basic is not available in VDG Sense 2.5 or higher!


Tripwire
A tripwire is a line drawn within the camera’s field of view. An object triggers a response by crossing the line. Tripwires can be created along perimeters (such as fence lines), in front of entryways, and along other restricted areas. Depending on how a tripwire event is set up, a response can be triggered when an object crosses the tripwire from left to right, from right to left, or in either direction. Tripwires can consist of one or more segments or multiple lines.

Standard Tripwire
A tripwire is a line drawn within the camera’s field of view. An object triggers a response by crossing the line. Tripwires can be created along perimeters (such as fence lines), in front of entryways, and along other restricted areas. Depending on how a tripwire event is set up, a response can be triggered when an object crosses the tripwire from left to right, from right to left, or in either direction. Tripwires can consist of one or more segments.

Trigger an alarm when an object crosses the line in the direction of the Arrow

Segmented Tripwire
See previous paragraph for explanation

Trigger an alarm when an object crosses the line in the direction of the arrows

Multiline Tripwire
A multi-line tripwire is two lines drawn within the camera’s field of view. An object triggers an alert by crossing both lines within a user-specified period of time. Multi-line tripwires are used for the same purposes as a singleline tripwires, such as perimeter protection and the protection of other restricted areas.

Trigger an alarm when an object crosses both lines in the direction of the Arrow

The most commonreasons to use a multi-line tripwire instead of a single-line tripwire are as follows:

  •  You can use multi-line tripwires in areas where you have tried to use single-line tripwires, but too many false alarms are being generated because of waves, shadows, trees blowing in the wind, etc.

  • You need to create a rule that detects changes in the direction in which objects are moving, such as a car turning down a restricted roadway.

Be aware of the following disadvantages of using multi-line tripwires that can make them less desirable than single-line tripwires in some cases:

  • Multi-line tripwire rules must be created in such a way that the duration between when the tripwires are crossed is neither too long nor too short and the two tripwires are likely to be crossed in the order specified. Some testing is required to determine the appropriate duration between crossing the two tripwires. If you misestimate the duration, events may be missed. 

  • In order to trigger an alert for a multi-line tripwire event, ObjectR must track an object as it crosses both tripwires. Most often, the reason an object is not tracked is that it is not visible within the camera’s field of view at some point. For example, if there is a boulder between the two tripwires and an object is blocked from the camera’s view because it moves behind the boulder before crossing the second tripwire, ObjectR may not be able to track the object, and an alert may not be triggered.

  • An individual who knows about a multi-line tripwire can avoid detection by waiting long enough between crossing the two tripwires. For this reason, you may want to use multi-line tripwires in conjunction with loitering and left behind events, to detect objects stopping between the tripwires.

Segmented Multiline Tripwire
Essentialy the same as the previously described tripwire. As an extention the tripwire is created using multpile tripwire segments, resulting in the ability to more closely follow realworld obstructions, like a curved fence.

Trigger an alarm when an object crosses both lines in the direction of the Arrow