Run geospatial queries
SedonaSQL provides various APIs to work with raster data, provided below are some functions.
The whole catalog of Raster functions provided by SedonaSQL can be found here
Sedona allows you to translate coordinates as per your needs. It can translate pixel locations to world coordinates and vice versa.
Use RS_PixelAsPoint to translate pixel coordinates to world location.
SELECT RS_PixelAsPoint(rast, 450, 400) FROM rasterDf
POINT (-13063342 3992403.75)
World to Raster Coordinate¶
SELECT RS_WorldToRasterCoord(rast, -1.3063342E7, 3992403.75)
POINT (450 400)
Use RS_Values to fetch values for specified array of Point Geometries. The coordinates in the point geometry are indicative to real world location.
SELECT RS_Values(rast, Array(ST_Point(-13063342, 3992403.75), ST_Point(-13074192, 3996020)))
To change values over a grid or area defined by a geometry, we will use RS_SetValues.
SELECT RS_SetValues( rast, 1, 250, 260, 3, 3, Array(10, 12, 17, 26, 28, 37, 43, 64, 66) )
Follow the links to get more details on the functions used in the examples.
Sedona provides APIs to select specific bands from a raster image and create a new raster. For example, to select 2 bands from a raster, you can use the RS_Band API to retrieve the desired multi-band raster.
Let's use a multi-band raster for this example. The process of loading and converting it to raster type is the same.
SELECT RS_Band(colorRaster, Array(1, 2))
SELECT RS_AddBand(raster1, raster2, 1, 2)
This will result in
raster2's specified band, at the specified index.
Resample raster data¶
Sedona allows you to resample raster data using different interpolation methods like nearest neighbor, bilinear, and bicubic to change the cell size (scaleX/scaleY), raster width/height or cell pivot, using RS_Resample.
SELECT RS_Resample(rast, 50, -50, -13063342, 3992403.75, true, "bicubic")
Execute map algebra operations¶
Map algebra is a way to perform raster calculations using mathematical expressions. The expression can be a simple arithmetic operations or a complex combination of multiple operations.
The Normalized Difference Vegetation Index (NDVI) is a simple graphical indicator that can be used to analyze remote sensing measurements from a space platform, and assess whether the target being observed contains live green vegetation or not.
NDVI = (NIR - Red) / (NIR + Red)
where NIR is the near-infrared band and Red is the red band.
SELECT RS_MapAlgebra(raster, 'D', 'out = (rast - rast) / (rast + rast);') as ndvi FROM raster_table
For more information please refer to Map Algebra API.
Interoperability between raster and vector data¶
Geometry As Raster¶
Sedona allows you to rasterize a geometry by using RS_AsRaster.
SELECT RS_AsRaster( ST_GeomFromWKT('POLYGON((150 150, 220 260, 190 300, 300 220, 150 150))'), RS_MakeEmptyRaster(1, 'b', 4, 6, 1, -1, 1), 'b', 230 )
The image create is as below for the vector is:
The vector coordinates are buffed up to showcase the output, real use case, may or may not match the example.
Spatial range query¶
Sedona provides raster predicates to do a range query using a geometry window, for example let's use RS_Intersects.
SELECT rast FROM rasterDf WHERE RS_Intersect(rast, ST_GeomFromWKT('POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))'))
Spatial join query¶
Sedona's raster predicates also have the capability to do a spatial join using the raster column and geometry column, using the same function as above.
SELECT r.rast, g.geom FROM rasterDf r, geomDf g WHERE RS_Interest(r.rast, g.geom)
These range and join queries will filter rasters using the provided geometric boundary and the spatial boundary of the raster.
Sedona offers more raster predicates to do spatial range query and spatial join query. Please refer to raster predicates docs.