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 DocumentMT0100P.N

©XsensTechnologiesB.V. MTiandMTxUserManualandTechnicalDocumentation

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4.6.3 Headingreset

OftenitisimportantthattheglobalZ‐axisremainsalongthevertical(definedbylocalgravityvector),butthe

globalX‐axishastobeinaparticulardirection.Inthiscaseaheadingresetmaybeused,thisisalsoknownas

“bore sighting”. When performing a heading reset, the new global reference frame is chosen such that the

global X‐axis points in the direction of the sensor while keeping the global Z‐axis vertical (along gravity,

pointingupwards).Inotherwords:ThenewglobalframehastheZaxisalonggravity,pointingupwards,theX ‐

axisintheplanespannedbytheverticalandthesensorX‐axis,perpendiculartotheglobalZ‐axisandtheY‐axis

suchthatarighthandedcoordinatesystemisformed.

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NOTE:Afteraheadingreset,theyawmaynotbeexactlyzero,thisoccursespeciallywhentheX‐axisiscloseto

thevertical.ThisiscausedbythedefinitionoftheyawwhenusingEulerangles,whichbecomesunstablewhen

thepitchapproaches±90deg.

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4.6.4 Objectreset

TheobjectresetfunctionaimstofacilitateinaligningtheMTi/MTxcoordinateframe(S)withthecoordinate

frame of the object to which the sensor is attached (O). After an object reset, the S coordinate frame is

changedtoS’asfollows:

• theS’Z‐axisisthevertical(up)attimeofreset

• theS’X‐axisequalstheSX‐axis,butprojectedonthenewhorizontalplane.

• theS’Y‐axisischosenastoobtainarighthandedcoordinateframe.

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NOTE: Once this object reset is conducted, both calibrated data and orientation will be output in the new

coordinateframe(S’).

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TheobjectresetcanbeusedtosettheMTi/MTxcoordinateframetothatoftheobjecttowhichitisattached

(see figure below). The sensor has to be attached in such a way that the X‐axis is in the XZ‐plane of the

objectcoordinateframe(situationA),i.e.theMTi/MTxcanbeusedtoidentifytheX‐axisoftheobject.To

preservetheglobalvertical,theobjectmustbeorientedsuchthattheobjectz‐axisisvertical.Theobjectreset

causesthenewS’coordinateframeandtheobjectcoordinateframetobealigned(situationB).

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NOTE:SincethesensorX‐axisisusedtodescribethedirectionoftheobjectX‐axis,theresetwillnotworkif

thesensorX‐axisisalignedalongtheZ‐axisoftheobject.

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sensor

coordinate

frame (S)

new sensor

coordinate

frame (S’)

Object

coordinate

frame (O)

Object

coordinate

frame (O)