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1、PIDF-LOProfileJamesWinterbottom,MartinThomsonIETF-65WhafsChanged? Updatedtherulesbasedoncommentstomakethemlessambiguous. RemovedmuchofthegeospatialsectionandmadeextensivereferencestotheGeoShapedraft. ModifiedexamplestobeinlinewithRevisedCivicdraftandGeoShapedraftIssues Recommendarestrictionofpolygon
2、to16pointswhentransportingownlocation. Dowewanttorecommendshapetypesforemergencycalling?LCIandUncertaintyLCIUncertaintyInLCI(RFC3825)definesaresolutionthatdescribesaregionofuncertainty.AppendixAofPIDF-LOProfiledescribeshowtogetaPIDF-LOfromLCI.ResolutionindicatesanumberofbitsthatcanbeconsideredvalidC
3、onvertingfromLCI(FromRFC3825)38.8986is-000100110.1110011000001111111001000Aresolutionof1indicatesarangeusingthefirst1bits:一00010011011100110OxxxxxxxxxxxxxxxxxbitscanhaveanyvaluefromallOstoall1s:-000100110.1110011ooooooooooooooooooto000100110.1110011001111111111111111-38.8984375to38.90039059519767761
4、23046875ConvertingtoLCI (RFC3825doesrTtincludeanyexampleofthis)WhenconvertingavaluewithuncertaintytoLCI，startwiththemaximumandminimumvalues:-32.98004to32.98054397(56metrerange)一000100000.1111101011100011111001110to000100000.1111101100000100111011100 Resolutionisthenumberofidenticalbits: 一000100000.1
5、111101,whichis16bitsConvertingbacktocheckaccuracy:-32.9765625to32.9843745(-870metrerange) ThatwasntacontrivedexampleThatwasarandomlyselectedpoint. Thisgetsmuchworseforcertainbordercases:一31.9999985to32.00000274(0.5metres)一000011111.1111111111111111111001110to000100000.0000000000000000001011100Theres
6、ultingresolutionisonly3bits!Conversiongivesarangefrom0to31.9999999701976776123046875Theerrorhasincreasedto3,500,000metres!Conclusion LCIencodinghasamajorflaw. Thisflawcausesittobreakdownnearcertainboundaries.一Thisproblemcanoccurallovertheworldwherevertheminimumandmaximumvaluesforalocationdifferintoo
7、manybits. Itdoesrftmatterwhattheoriginalprecisionwas!一AlocationwithuncertaintythatspanstheGreenwichMeridianortheEquatorcannotberepresented: Resolution=0bits!ResolutioniseffectivelyuselessFormynexttrick Iwilldemonstratehowimportantuncertaintyis. andwhyitshouldnotbeignored.ZoneBWhereistheTarget:ZoneAo
8、rB?ZoneAThisiseasy:itsclearlyinZoneA,right?WhereistheTarget:ZoneAorB? Ifyouineludeuncertainty,theanswerislessclear. Tobecertain,theoverlapwithZoneAmustbecomparedwiththeoverlapwithZoneB.WhereistheTarget:ZoneAorB? TheamountofuncertaintydetermineswhichzonetheTargetismostlikelytobein. Thebiggertheuncertainty,themorelikelytheTargetisinZoneB.
