图论中间件技术学习：rasterNULL 博文链接：https://flyqantas.iteye.

文件名称: 图论中间件技术学习：raster

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详细说明：NULL 博文链接：https://flyqantas.iteye.com/blog/22164511- The Canadian Spatial Data Foundry The problem Researchers must learn lots of ArcGIs, to use only a few operations search for, download and assemble large datasets historical data are often lost data are delivered in many different formats datasets are too large to fit in one file(shp limited to 2 GB, complete forest cover for Canada is 30GB, complete DEM for Canada is 9 GB, etc computation is often too difficult for ArcGIs (800 buffers over 5 000 000 polygons) struggle for weekS, if not months, to get their data table ready for statistical analysis In brief: researchers waste much energy on tasks unrelated to their main priority: research!!! The Canadian Spatial Data Foundry The Envisioned solution Building a paying web service Backed by a spatial database(PostGis)hosted on a supercomputer Administrators upload preassembled datasets of ecological layers (vector raster, historical data included) Users with accounts upload their datasets(shapefiles Create intersection queries on the ecological layers Obtain resulting shapefiles or tables(minutes, hours or days later) T polypi Users Web server Supercomputer Administrators shapefiles Web service PostgreSQL PostGIs geospatial data queries SQL users layers intersections table or ecological layers shapefile The Canadian Spatial Data Foundry What is a spatial database? DBMS with native support for the geometry type Normalisation shapefile spatial DB Standard Query Language (SQL) properties properties districts Transactions Rules shape owner geometry owner geometry id polygon/ Jean polygon Jean polygon AB12 Security Backup polygon Pierre polygon Pierre polygon CF34 Functions Operators polygon Marc polygon Marc polygon RT43 polygon Jean polygon Jean polygon RE42 (intersect, within, area0, ,&&,etc) SELECT area(geometry), owner FROM properties, districts WHERE intersect(properties. geometry, districts. geometry)and district id ="AB12 What is the area- and who is the owner-of properties located in district AB12? IBM DB2 Spatial Extender, Informix Spatial Data Blade(Oracle Spatial PostgreSQL/Post GIS, ESRI's ArCSDE, Intergraph's GeoMedia What about raster Raster Support Requirements 1- Storage of Non Rectangular Raster Coverage We have to be able to store not only"ideal rectangular raster datasets Real" Raster Dataset dea” Raster Dataset landcover tiled raster raster BLOl aster BLOB 3 raster BLOB raster BLO 5 rasterBLO 53 raster BLOI >54 rasterBLOB e.g. SRTM Coverage for Canada but also“real”non- rectangular raster coverages Raster Support Requirements 2- Easy Importation/Exportation import PostgreSQL PostGis export ecological layers The way to import raster layers should not differ much from the way to import vector layers Raster Support Requirements 3- SQL Functions Operators on the Raster Type Raster Attributes area(, srido, width, height, pixeltype(, pixelsizeo3 nodatavalue(, georeference(, etc Raster Transformation reprojecto, translate, scale(, resample(, clip(, reclasso3 mapalgebra,etc… Raster Aggregation Merge of many rasters using GROUP BY(accum) Raster Conversion toJPEGO, toTIFFO, to KMLO, toPolygon(. Raster Support Requirements 4- LosSless Conversion Between Vector and Raster Layers Categorical rasters layers convert well to vector layers one variable converts to one column groups together pixels of same value contiguous or not landcover landcover continuous raster lavers do not convert as well geometry type polygon polygon Vector layers do not convert well to raster layers polygon 7 each attribute(e.g type) must be 田 converted to one raster no support for nominal values(e.g."M34) global values(area) lose their meaning 国圆圆 overlaps are lost landcover resolution must be high to match vector ometry type mapsheet area olygon 4 M341334 precIsion polygon 3 M331543 area features lose their unique identities polygon 7 M3310.56 reconversion to the original vector is very difficult or impossible We need a better way to convert vector layers to rasters without destroying the objects identities Raster Support Requirements 4- LosSless Conversion Between Vector and Raster Layers In a vector layer, each object has its own identity landcover geometry type mapsheet area polygon M3413.34 polygon M3315.43 polygon 7 M3310.56 polygon M3424.54 loligo 5 M3323.43 polygon 2 M32 12.34 In a raster layer converted from a vector layer, each object should conserve its own identity landcover raster type mapsheetarea raster 4 M341334 raster 3 M331543 raster M3310.56 raster 9 M34 24.54 raster 5 M3 23.43 raster 2 M321234 Each raster object has its own georeference Rasters become just another way to store Black pixels are"nodata values geographic features in a more expressive Like vectors, raster objects may or may not overlap vector object-oriented-like style Raster algorithms can be used on the whole layer after a"blend" of the objects into a single raster

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