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logic_measure_movement is a point entity available in all Source games. This entity measures the movement of an entity relative to another entity and then applies that movement to a third entity.

logic_measure_movement's process can be described like this:

  1. The position of the Entity to Move is obtained. Let's say it's [100 225 0].
  2. The position of the Measure Reference is obtained. Let's say it's [50 300 0].
  3. The position of the Entity to Move is subtracted by the position of the Measure Reference, creating a "relative position" difference. In this case, it would be [100 225 0] - [50 300 0], which equates to [50 -75 0].
  4. The position of the Movement Reference is obtained. Let's say it's [150 50 100].
  5. The "relative difference" position is added onto the position of the Movement Reference. In this case, it would be [50 -75 0] + [150 50 100], which equates to [200 -25 100].
  6. The Entity to Move is teleported to the sum of the "relative difference" position and the position of the Movement Reference, which in this case means the entity is teleported to [200 -25 100].

logic_measure_movement is very flexible and can be used to make one entity mimic the movement of another from another room (e.g. a point_camera in a script_intro). It can also be used to serve as an alternative to parenting, especially since it can simulate parenting on physics objects, which don't support parenting and would normally use phys_constraint.

Warning.png Warning: Does not properly update collision physics on the object being moved.
Code:By default, logic_measure_movement calls SetAbsOrigin directly. Using Teleport instead updates entity interpolation correctly and may or may not solve the collision physics warning described above.


Entity to Measure <targetname>
Entity whose movement you want to measure.
Measure Reference <targetname>
The movement of Entity to Measure will be measured relative to this entity.
Entity to Move <targetname>
This entity will be moved to mimic the motions of Entity to Measure.
Movement Reference <targetname>
The Entity to Move will move relative to this entity.
Movement scale <float>
A scale to divide the measured movements by, before applying those movements to the Entity to Move.
1 = target entity moves as much as the measured entity,
2 = target entity moves half as far as the measured entity, and
0.5 = target entity moves twice as far as the measured entity.
Measurement Type <choices>
What to measure.
  • 0 : Position
  • 1 : Eye position


Name (targetname) <string>
The targetname that other entities refer to this entity by.
Entity Scripts (vscripts) <scriptlist> (in all games since <Left 4 Dead 2>)
Space delimited list of VScript files (without file extension) that are executed after all entities have spawned. The scripts are all executed in the same script scope, later ones overwriting any identical variables and functions.
Script think function (thinkfunction) <string> (in all games since <Left 4 Dead 2>)
Name of a function in this entity's script which will be called automatically every 100 milliseconds (ten times a second) for the duration of the script. It can be used to create timers or to simulate autonomous behavior. The return value (if present) will set the time until the next call.
Note.png Note: Try to avoid expensive operations in this function, as it may cause performance problems.


SetMeasureTarget <string>
Set the Entity to Measure, whose movement should be measured.
SetMeasureReference <string>
Set the Measure Reference entity.
Target <string>
Set the Entity to Move, which will be moved to mimic the measured entity.
SetTargetReference <string>
Set the Movement Reference entity.
SetTargetScale <float>
Set the scale to divide the measured movements by.
Enable the logic_measure_movement.
Disable the logic_measure_movement.


Removes this entity from the world.
Removes this entity and its children from the world.
Note.png Note: Entities already remove orphaned children upon being removed, but this input removes all children on the same frame, being marginally faster than Kill.
AddOutput <string>
Adds a keyvalue/output to this entity. It can be potentially very dangerous, use with care.
KV Format: <key> <value>
I/O Format: <output name> <targetname>:<inputname>:<parameter>:<delay>:<max times to fire, -1 means infinite>
FireUser1 to FireUser4
Fire the OnUser outputs; see User Inputs and Outputs.
Use  !FGD
Same as a player invoking +use; may not do anything depending on the entity. Can also be invoked by firing an output that does not specify an input.
RunScriptFile <script> (in all games since <Left 4 Dead 2>)
Execute a VScript file from disk, without file extension. The script contents are merged with the script scope of the receiving entity.
RunScriptCode <string> (in all games since <Left 4 Dead 2>)
Execute a string of VScript source code in the scope of the entity receiving the input. String quotation may be needed when fired via console.
Bug.png Bug: In <Left 4 Dead 2>, the code is executed in the script scope of the entity that fires the output, not the one receiving the input.
Warning.png Warning: Never try to pass string parameters to a script function with this input. It will corrupt the VMF structure because of the nested quotation marks, which then must be removed manually with a text editor.
CallScriptFunction <string> (in all games since <Left 4 Dead 2>) !FGD
Execute a VScript function in the scope of the receiving entity.
SetLocalOrigin <coordinates> (in all games since <Alien Swarm>) !FGD
Send this entity to a spot in the map. If the entity is parented to something, it will be offset from the parent by this amount.
SetLocalAngles <angles> (in all games since <Alien Swarm>) !FGD
Set this entity's angles.



OnUser1 to OnUser4
These outputs each fire in response to the firing of the like-numbered FireUser1 to FireUser4 Input; see User Inputs and Outputs.
OnKilled  (only in <Left 4 Dead><Left 4 Dead 2>)
This output fires when the entity is killed and removed from the game.