Simrad ES80 - Page 458

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referencedtotheorigin.Inmostcases,thelocationofthevessel’s"ofcial"origin
hasbeendenedbythedesignerorshipyard.Thisoriginisnormallyidentiedwitha
physicalmarking,andalsoshownonthevesseldrawings.
Frequentlyusedlocationsare:
•Aftimmediatelyovertherudder(frame0)
•Vessel’scentreofgravity
•Thephysicallocationofthemotionreferenceunit(MRU)
Coordinatesystemalternativeorigins
Ifnecessary,otheroriginlocationsmaybedenedforspecicproductsorpurposes.One
exampleistheNavigationReferencePointthatisfrequentlyused.Wheneveravessel
issurveyedtoestablishaccurateoffsetinformation,thesurveyormayalsoestablishan
alternativeoriginlocation.Wheneverrelevant,anysuchalternativelocationsmust
bedenedusingoffsetvaluestothe"ofcial"originestablishedbythedesigneror
shipyard.Acommonlyusedalternativeoriginisthephysicallocationofthevessel’s
motionreferenceunit(MRU).
Deningthephysicallocationofeachsensor
Bymeansofthevesselcoordinatesystem,thephysicallocationofeverysensorcan
bedenedusingthreenumericalvaluesforX,YandZ.Thesevaluesmustdenethe
verticalandhorizontaldistancesfromasinglereferencepoint;theorigin.Thephysical
locationofthemotionreferenceunit(MRU)isoftenthemostimportantsensortodene.
Formanysystems,thevesselheadingisalsoacriticalmeasurement.
Inthisexample,asecondreferencepointhasbeen
established.Itisdenedwiththreepositiveoffsetvalues
forX,YandZ.Allvaluesarepositivebecausethenew
referencepointisinfrontofandbelowtheorigin,andon
thestarboardside.
Theaccuracyofthethree
numericalvaluesfor
X,YandZdenesthe
accuracyofthesensor
data.Ifyourequireahigh
accuracy,forexamplefor
underwaterpositioning,
underwatermappingor
scienticmeasurements,
youmusthaveeach
sensorpositioned
usingprofessionalland
surveying.Forsuch
use,agoodalignment
surveyiscriticalforhigh
qualityresults.Surveysarenormallydonebyqualiedandtrainedsurveyorsusing
provensurveyequipmentandmethods.
Relatedtopics
SensorInstallationpage,page363
SimradES80ReferenceManual