Hemisphere Detection

Option: Use Plane for Hemisphere Detection

This option defines how the sensor determines its valid starting position relative to the source. When enabled, AMFITRACK uses a reference plane to decide on which “side” (hemisphere) the sensor must be located to initialize correctly. Noted that once this algorithm completes it can’t be overwriten without unless tracking is lost, unlike “Assume Plane for Hemisphere Detection”.

Hemisphere Detection Normal Vector

These parameters define the orientation of the detection plane’s normal vector:

  • Hemisphere detection normal vector X

  • Hemisphere detection normal vector Y

  • Hemisphere detection normal vector Z

The combination of these three values specifies the direction of the plane’s normal vector. AMFITRACK uses this direction to determine which side of the plane is valid for sensor initialization.

Example: Sensor above the source

  • Hemisphere detection normal vector X = 0

  • Hemisphere detection normal vector Y = 0

  • Hemisphere detection normal vector Z = 1

Result:

  • The normal vector points upward along the Z-axis.

  • The system considers the hemisphere above the source as the valid area.

  • When you hold the sensor above the source, it will initialize correctly.

You can change the normal vector direction to configure other valid hemispheres (e.g., in front, behind, or below the source).

Understanding and Changing the Normal Vector

The normal vector defines a direction in 3D space. It tells AMFITRACK which side of the detection plane should be considered the valid hemisphere for correct sensor initialization. The vector is described with three values:

  • X → points behind the source (USB connector side)

  • Y → points to the right side of the source

  • Z → points upward from the source

Each value can be any (float) value depending on the direction you want. Together, they describe a vector direction pointing outward from the source.

Practical examples:

  • X = 0, Y = 0, Z = 1 → Upwards (sensor above the source)

  • X = 0, Y = 0, Z = -1 → Downwards (sensor below the source)

  • X = 1, Y = 0, Z = 0 → Behind the source (USB side)

  • X = -1, Y = 0, Z = 0 → In front of the source (opposite USB)

  • X = 0, Y = 1, Z = 0 → To the right of the source

  • X = 0, Y = -1, Z = 0 → To the left of the source

  • X = -1, Y = 0, Z = 1 → Upwards and forward (sensor is on the correct side of the 45 degree plane the source)

Note

The vectors can be scaled to any length and will have the same effect.

Tips for choosing the right vector:

  1. Think about where your sensor will be positioned relative to the source

when starting. Consider the entire volume you are likely to start in. Think particularly about the edges of your desired startup volume. (If the likely startup positions/volume exceed what can fit into one abitrary hemisphere of the source, then read “Hemisphere Detection Distance Threshold” after finishing the steps here.)

  1. Start your sensor manully and check that is tracking correctly. Be sure that the status is tracking and Verify it using several diferenet positions and orientations.

  2. Place the senor in the center of your tacking volume. Manully note the current position of the sensor (orientation is not important).

  3. Enter the position as the normal vector. The sensor will now use your desired starting location.

Hemisphere Detection Distance Threshold

This parameter defines the minimum distance from the detection plane at which the sensor is considered valid. If the distance between the senor and the hemisphere detection plane is less than the threshold it will not accept the hemisphere. This effectively creates a dead-zone where signing will not hemisphere detection.

If some of the desrired startup volume crosses or is close to the plane it is prone to cause errors or Incorrect startups. Consider using “Assume Plane for Hemisphere Detection” to correct when the errors occour. If that is not an option for what ever reason “Hemisphere Detection Distance Threshold” is a strong reliable alternative. It limits the start up volume. But in return it means that the user has to mess up far more before they get an incorrect autostart.

  • If the sensor is too close to the plane (within this threshold), the hemisphere detection will not trigger.

  • Decreasing the threshold allows more tolerance but may result in more incrorrect autostarts.

  • Increasing the threshold requires stricter positioning relative to the plane. But allows for greater reliabilty.

Option: Assume Plane for Hemisphere Detection

Uses the same algorithm as “Use Plane for Hemisphere Detection”. The main difference that an extra check is performed this means that even if the sensor is placed incorrectly relative to the hemisphere-plane during startup it still has a chance to correct the result.

More speciffically, after completing the the startup and starting tracking the sensor will enter the status “Verifying Hemisphere”. While in this status the sensor will attempt to verify the hemisphere based of the movements it is exposed to. Note that when verification completes it may overwrite the initial tracking. Typacilly this will be correct, but it may sometimes be Incorrect. After this the sensor will enter stauts “tracking” and it will no longer be able to overwrite the hemisphere unless tracking is lost.