Hierarchicaldataorganization
People’sperceptionoftherealworldisoftenlimitedtoasmallareaoracertainindividualobject.TheserealworldobjectsarecalledAnentityisanobjectivelyexistingobjectwithcertaincharacteristics.Atypeofentitywithcertaincommoncharacteristicscanbecalledanentitygroup;inaddition,therearemanygeographicalphenomenaonthesurface,whichcanbedescribedbyfields,forexample,Terrainelevation,airtemperature,soilmoisture,etc.;accordingtothedatatypeofthedependentvariable,thefieldcanbedividedintotwotypes:continuousfieldanddiscretefield.Infact,anygeographicalphenomenoncanbeexpressedthroughthefield.However,inmanycases,amethodcanprovideabetterbasisforeffectivecalculations,anditmayalsobeabettermodelforpeople'spsychologicalexpressionofgeographicphenomena.Forexample,thestateorprovinceofacountryisusuallyexpressedinGISasagroupofareaobjectsoragroupoflineobjectsformingitsboundary;ofcourse,itcanalsobeexpressedasadiscrete2-dimensionalfield.Entityandfieldcananswerdifferentquestions(whereandwhat)respectively.Ofcourse,theprocessofansweringquestionsmustbebasedontime(when).ThiswayofcognitionresultsinahierarchicaldataorganizationmethodinGIS,thatis,thestructureofgeographicentitiesintomathematicalpoints,lines,areas,andgridcells(grid).
Thehierarchicalclassificationtheoryisoneofthebasictheoriesforpeopletoperceivetherealworld."Layer"isanimportantbasicconceptinGIS,and"Layer"isoneofthemostbasicandimportantmethodsofGISdataorganization,asshownintheupperdiagraminFigure1.Hierarchyinthevectormodelisaccompaniedbyclassification(mainlyreferstotheclassificationofabstractgeometricelements,suchaspoint,line,surface,andbody,etc.).Therastermodelismainlyhierarchical,andeachlayerofdataafterlayeringhasCorrespondingattributesandspaceandotherinformation,thelogicalorganizationmodelisshowninthefigurebelow.
GISdataisorganizedbyseveralspatialdatalayersandtheirrelatedattributedata.Aspatialdatalayerisstoredintheformofseveralspatialcoordinatesorrasterpixels.Thislogicalorganizationmodelcanbesummarizedascoordinatepair-spatialobject-layer-map.Aspatialobjectanditsattributeinformationbelongtothemostbasiclevelinthismodel,andthemapisthehighestlevelofthismodel.Theinformationinthegeographicdatalogicalorganizationmodelcanbeclassifiedasfollows:
(1)АтласТова е най-високата информация в организацията на географски данни, която управлява целия атлас и обработва всяка карта, за да идентифицира различни карти, включително следната информация: предпочитание за карта (име на таблица, номер на играч на карта и т.н.), координати на карта (координатна система, информация за регистрация и т.н.), описание на картата (права за достъп, карта описание и др.) и друга информация.
(2)Набор от слоевеТози набор от слоеве е съставен от множество пространствени слоеве, които могат да отговорят на определени изисквания за приложение, включително препратки към слоеве (етикет на слой, име на таблица на слой), индекс на пространство на слой (размер, етикет, име на таблица), дисплей на слоя, диапазон на координати на слоя (максимални и минимални координати) и друга информация.
(3) Слой Това е колекция от множество пространствени обекти от един и същи тип с определени еднакви или подобни характеристики, включително идентификация (етикет, име) и описание на пространствения обект (Име, характерен атрибут, тип), геометрично представяне на пространствени обекти (двоичен голям обект-BLOB форма на координати).
TheaboveisthedataorganizationmethodofGISverticallayering.Thislayereddataorganizationismap-oriented.Inthedatabase,thelibrary—mapsheet—layer—geographicalobject—geometricobjectisgenerallyused.Dataorganizationstrategy.Horizontally,GISdataisorganizedbyframingordividinggrids(tiles),andthentheyarespatiallyindexed.Thiskindofdataorganizationisrealizedinthecomputerthroughtheseparationofgraphichierarchicalfilemanagementandattributedatarelationaldatabase(RDBMS)management.Therearetwoways:oneistoembedRDBMSintotheGISsystemInternal;theotheristouseanextendedRDBMStomanageattributedatainadditiontotheinternalRDBMS.TheconnectionbetweenspatialdataandattributedataiscompletedbythekeyID.
Организация на данни, базирана на функции
Описанието на географски феномени, базирано на йерархична организация на данни, има следните недостатъци:
(1)Real-worldspatialgeometrytargetsAbstractionignorestheessentialcharacteristicsofgeographicphenomenaandtheirinternalconnections,andartificiallydividestherealworld,whichresultsinthesimplificationofGISinformationandreducesthecapacityofGISinformation.
(2)PayattentiontothedescriptionofspatiallocationsThevectororrasterdataorganizationmodelofthecompanylosestherichanalysiscapabilitiesprovidedbythestructuredentitiesbasedontheclassificationattributesandinterrelationships;
(3)TheoverlapmethodTherealworldisdividedintoaseriesoflayerswithstrictboundaries,buttheseboundariescannotfullyreflecttheobjectivereality,whichcausesmanyhumanerrors;inaddition,thismethodcannotprovidethespatialanalysiscapabilitiesofmanybasicobjects.
Actually,inthehierarchicaldataorganization,point,line,surface,andgridunitsdonotexist.Inreality,roadsarenotmathematicallines,andcitiesarenotmathematicalpoints.Thisabstractionisnotadescriptionorexpressionofrealgeographicspace.Theperceptualworldaroundusisasetofmaterialentitieswithhighlycorrelatedstructures,thatis,theseentitieshaveasetofcommonattributesthatallowpeopletoclassifyonthebasisofsimilarity.Therecognitionofthecommonalityofgeographicentityattributesandrelationshipsisthestartingpointofpeople'scognition(Usery1993).Itcanbeseenthatpeople'sfirstknowledgeoftheobjectiveworldisbasedongeographicfeatures,andthiswayofcognitioncreatesamethodofdataorganizationbasedongeographicfeatures.ISO/TC211andOGCrespectivelydefinegeographicfeatures:
(1)AccordingtothedefinitionofISO/TC211,featureshavetwolevels:featuretypesandfeatureinstances.Featuretypesaregeographicphenomenawithcommonattributes.Afeatureinstanceisaspecificgeographicphenomenonofafeaturetype;eachfeatureinstancehasauniqueidentifier,whichisencapsulatedwithattributes,functionsandrelationships,andcancomprehensivelydescribethecharacteristicsoftheoccurrenceanddevelopmentofthefeaturetype.Symbols,aseriesofcharacteristicstatesoreventscanbeorganicallylinkedandorganizedtogether,andcanbepositionedinthespace-timecoordinatesystem,whichisconducivetothemanagementandqueryofspace-timedata;
(2)DefinitionofOGC,Featureisthebasicunitofgeospatialinformation;Inaddition,USGISintheUnitedStatesalsogivesitsowndefinitionoffeature:Featureisanentityortarget(digital/orgraphic)expressionoftheobjectiveworld.Itcanbeseenthatafeatureisadescriptionorexpressionofarealgeographicalphenomenon.Thisgeographicalphenomenoncanbearealgeographicalentity,suchasariverorlake,oritcanbeaclassificationresult,suchasdifferenttypesofland,orItisameasurementresultofacertainphenomenon,suchashightemperaturearea,highrainarea,etc.Therefore,ageographicfeatureisageographicentitythatexistsobjectivelyontheearthandhasdescriptiveinformation,andthisgeographicentitycanbedefinedbyitsidentificationanddescriptionofitsattributesandrelationships.
Thebasisoffeature-basedGISdataorganizationisfeatureclassification.Itdirectlyaffectstheeffectivenessofgeographicdataorganization,management,queryandanalysis;itaffectsthecompletenessofgeographicdatamodelsemanticsanddatasharing.Therefore,feature-basedGIScanbeconstructedusingobject-orientedtechnology.Itsdataorganizationframeworkneedstousetherelevantconceptsofcognitiveclassificationtheoryandtherelevantmethodsofcartography.Thismethodofdataorganizationrequiresacorrectandappropriategeographicclassificationsystem.Whilefollowingthegeneraltaxonomyprinciples,thesystemmustalsoconsidertheneedsofGIStechnology(suchasobject-orientedtechnology).Itrequiresthattheclassificationsystembeincorporatedintoanon-spatialattributeInthedeterminedspacesystem.
Comparativeanalysisofthetwomethods
Thehierarchicaldataorganizationandthefeature-baseddataorganizationareatthesamelevelofabstraction.Botharebasedontheentitymodelandthefieldmodel,butFeature-baseddataorganizationusesobject-orientedtechnicalmethodstoorganizedataonthebasisofobject-orienteddatamodels,whilehierarchicaldataorganizationmainlyuseshierarchiesonthebasisofvectordatamodels,rasterdatamodels,andrelationaldatamodels.Themethodtoorganizedata;althoughwiththecontinuousdevelopmentandimprovementoftechnicalmeans,thelayereddataorganizationmethodhasalsoinfiltratedtheobject-orientedtechnology,butthisdoesnotconstituteatrueobject-orienteddatamodel.Itcanbeseenthatthereisafundamentaldifferencebetweenthetwo.
AsshowninFigure2,thesamegeographicphenomenonusesahierarchicaldataorganizationmethodtobedividedintoatleast3layers(points,lines,andareas),whileusingadataorganizationmethodbasedongeographicfeaturesonlyrequires1layer.,Andthespatialrelationshipbetweenthemisobvious.However,whetheritishierarchicalorfeature-baseddataorganization,itisinseparablefromtheanswerstothreebasiccognitivequestions,namelywhere,whatandwhen.
Spatialdataorganization
Intermsofdatamanagement,GISwillstorespatialdataandattributedatainthegeometricsenseseparately,andusefilesanddatabasemanagementrespectively.ThefuturedevelopmenttrendisapplicationObject-orientedmathematicalmodelandspatialdatawarehousetechnologythatusesadatabasetomanagemassiveamountsofdatainarealsense.
Следвайки горните принципи, широкомащабната организация на GIS данни, която отговаря на изискванията на „цифровата земя“, е следната:
(1)Векторни данни: Съхраняват се отделно според рамката на картата и мащаба.
(2)Rasterdata:regulargriddatawithacertaingridspacing(suchasDEM,imagedata,etc.),anditsdataorganizationisdifferentfromvectordata.Duetotheinfluenceofmapprojection,whenthedataisstoredingeographiccoordinates(latitudeandlongitude),thenumberofgridscontainedineachstandardframingmapisthesame,andthedataformsastandardrectangle;andwhenthedataisstoredinrectangularcoordinates(x,y)Whenstoring,thequantitycontainedineachstandardframingmapformsatrapezoid(approximately).Inordertosolvetheproblemofdataconnection,generallythecircumscribedrectangleofthefigureprofileisusedastheboundarytoformastandardrectangle,andthedataoutsidethefigureprofileFillitwithadjacentmapframedata,asshowninFigure3.
Duetotheunequalsizeoftheoriginaldata,dataconnectionproblemsareoftenencounteredduringdataroaming.Therearemanywaystosolvethisproblem.Amorefeasiblemethodistore-splicethedataandcutdatablocksofuniformshapeandsize.Inthisway,indataroaming,thesplicingofadjacentdatablocksisextremelysimple,whichavoidsdataredundancy.Iimprovedtheefficiencyofthesystem.Thedatacuttingrulesare:
①Поставете всички данни под пространствената координатна рамка на „цифровата земя“.
②Независимо от всякакъв мащаб и разстояние в мрежата, всеки файл с данни (блок с данни) има единен размер.
③Разрушете концепцията за мащаба и използвайте разделителна способност (разстояние в мрежата) като мащаб за данни.
④Establishfiledescriptioninformation,andrecordtheresolution,projectionzonenumber,filelocationandotherrelatedinformationofeachfileforeasysystemcall.
(3)IntegrationofvectordataandrasterdataDuetothedifferentdatastructure,dataorganizationanddisplaymethodsofvectorandraster,theintegrationofvectordataandrasterdatarequiresthefollowingprocess:
①Datamatchinganddisplay:includingunifiedprojection,scalematchingandcoordinatematching.
②Theconversionofvectordataandrasterdata:Thisconversionincludestheconversionofpoints,lines,andareas.Theconversionfromvectordatatorasterdataisrelativelysimple.Inpracticalapplications,thisconversionisoftenused.