FAQs for the SpacePoint family
- How is the SpacePoint Fusion different from other motion-based gaming controllers, such as Nintendo's Wii Mote or Wii MotionPlus?
- My application is battery powered. Will the batteries have any effect on the sensors performance?
- The area I want to mount the sensors/module is near a motor, is that going to be a problem?
- What are quaternions, why do you use them, and how can I use them to get heading, pitch, and roll information (Euler angles)?
How is the SpacePoint Fusion different from other motion-based gaming controllers, such as Nintendo's Wii Mote or Wii MotionPlus?
Nintendo's Wii Mote only incorporates accelerometers: these are useful for measuring which way is down (gravitational acceleration)and for measuring linear non-gravity acceleration (such as a punching motion). The Wii MotionPlus adds gyroscopes, which means rotational acceleration can be monitored (such as when you throw a Frisbee or swing a golf club). But, the MotionPlus requires resetting on a fairly regular basis (after <1 minute of intense activity) since the gyros drift. PNI's SpacePoint technology adds PNI's magnetometers, which measure Earth's magnetic field and consequently provide an absolute orientation reference. Consequently, PNI's SpacePoint algorithms work in a similar manner to the Wii MotionPlus, except the SpacePoint algorithms are constantly "resetting" the controller such that consistent and accurate gameplay can run for an unlimited time.
My application is battery powered. Will the batteries have any effect on the sensors performance?
That depends on the location of the battery relative to the sensors, the type of battery used, and the PNI product being used. For instance, PNI's CompassPoint and FieldForce family of products incorporate PNI's proprietary hard and soft-iron correction algorithms which compensate for the magnetic distortion effects introduced by batteries. Still, it is recommended the sensors be mounted as far away from batteries as possible. This is especially true when using any type of rechargeable battery, as they tend to change characteristics during discharge and after each charging cycle. As to the types of batteries, Lithium has the least magnetic signature, followed by Alkaline, with NiCad (Nickel-Cadmium) having the highest magnetic signature.
The area I want to mount the sensors/module is near a motor, is that going to be a problem?
Since electric motors usually generate magnetic fields that are much stronger than the earth’s field, being in close proximity to the sensors could cause a hard-iron type distortion. It is recommended that the sensors be moved as far away from any motors as possible, but if that is not possible then shielding a motor may help reduce the distortion. Unfortunately, shielding the motor also may cause a soft-iron distortion due to the shielding materials used. Trial and error may be needed to find a location and/or shielding method that will work best in your application.
What are quaternions, why do you use them, and how can I use them to get heading, pitch, and roll information (Euler angles)?
Quaternions are used to represent orientation and rotation in space. As the name implies, 4 parameters are used to represent orientation with a unit quaternion. This compares with 3 parameters (heading, pitch, and roll) which are used with Euler angles. Quaternions can be preferable to Euler angles because they are easier to mathematically manipulate and Euler angles experience a singularity when pitch is +/-90 degrees (ie. Gimbal lock can occur).
Conversion from quaternions to Euler angles is relatively straightforward, as described below. For clarity sake, atan2 is a mathematical function that incorporates 2 arguments, it is not the square of arctan.
Quaternion parameters: q[0], q[1], q[2], q[3]
pi = 3.14159265
Conversion (to degrees):
For more information on quaternions and atan2, see Wikipedia at the addresses below:
Quaternions & Spatial Rotation
Conversion from Quaternions to Euler Angles
Definition of atan2