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)AtlasToto je informace nejvyšší úrovně v organizaci geografických dat, která spravuje celý atlas a zpracovává každou mapu, identifikuje různé mapy, včetně následujících informací: reference mapy (název tabulky, číslo vrstvy mapy atd.), souřadnice mapy (souřadnicový systém, registrační informace atd.), další informace. popis mapy (popis a přístupová práva)
(2)Sada vrstevToto je sada vrstev složená z několika prostorových vrstev, která může splňovat určité požadavky aplikace, včetně referencí vrstvy (označení vrstvy, název tabulky vrstvy), index prostoru vrstvy (velikost, popisek, název tabulky), zobrazení vrstvy, rozsah souřadnic vrstvy (maximální a minimální minimální souřadnice) a další informace.
(3)VrstvaToto je sbírka několika prostorových objektů stejného typu s určitými stejnými nebo podobnými vlastnostmi, včetně identifikace (štítek, název) a popisu prostorového objektu (Název, charakteristický atribut, typ), geometrické zobrazení řadových prostorových objektů (souřadnic BLOB ve tvaru binárních objektů).
TheaboveisthedataorganizationmethodofGISverticallayering.Thislayereddataorganizationismap-oriented.Inthedatabase,thelibrary—mapsheet—layer—geographicalobject—geometricobjectisgenerallyused.Dataorganizationstrategy.Horizontally,GISdataisorganizedbyframingordividinggrids(tiles),andthentheyarespatiallyindexed.Thiskindofdataorganizationisrealizedinthecomputerthroughtheseparationofgraphichierarchicalfilemanagementandattributedatarelationaldatabase(RDBMS)management.Therearetwoways:oneistoembedRDBMSintotheGISsystemInternal;theotheristouseanextendedRDBMStomanageattributedatainadditiontotheinternalRDBMS.TheconnectionbetweenspatialdataandattributedataiscompletedbythekeyID.
Organizace dat podle funkcí
Popis geografických jevů založených na hierarchické organizaci dat má následující nedostatky:
(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.
V souladu s výše uvedenými zásadami je organizace dat GIS ve velkém měřítku, která splňuje požadavky „digitální země“, takto:
(1)Vektorová data:Uloženo samostatně podle rámce mapy a měřítka.
(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:
①Umístěte všechna data pod prostorový souřadnicový rám „digitální země“.
②Bez ohledu na jakékoli měřítko a rozteč mřížky má každý datový soubor (blok dat) stejnou velikost.
③Rozbijte koncept měřítka a uživatelského rozlišení (rozteč mřížky) jako měřítko dat.
④Establishfiledescriptioninformation,andrecordtheresolution,projectionzonenumber,filelocationandotherrelatedinformationofeachfileforeasysystemcall.
(3)IntegrationofvectordataandrasterdataDuetothedifferentdatastructure,dataorganizationanddisplaymethodsofvectorandraster,theintegrationofvectordataandrasterdatarequiresthefollowingprocess:
①Datamatchinganddisplay:includingunifiedprojection,scalematchingandcoordinatematching.
②Theconversionofvectordataandrasterdata:Thisconversionincludestheconversionofpoints,lines,andareas.Theconversionfromvectordatatorasterdataisrelativelysimple.Inpracticalapplications,thisconversionisoftenused.