Add documentation

docs/api/sql/Raster-operators.md

@@ -22,6 +22,24 @@ Output:
 POINT (156.5 -75.5)
 ```
 
+### RS_PixelAsCentroids
+Introduction: Returns a list of the centroid point geometry, the pixel value and its raster X and Y coordinates for each pixel in the raster at the specified band.
+Each centroid represents the geometric center of the corresponding pixel's area.
+
+Format: `RS_PixelAsCentroids(raster: Raster, band: Integer)`
+
+Since: `v1.5.1`
+
+Spark SQL Example:
+```sql
+SELECT ST_AsText(RS_PixelAsCentroids(raster, 1)) from rasters
+```
+
+Output:
+```
+[[POINT (-13065222 4021263.75),148.0,0,0], [POINT (-13065151 4021263.75),123.0,0,1], [POINT (-13065077 4021263.75),99.0,1,0], [POINT (-13065007 4021261.75),140.0,1,1]]
+```
+
 ### RS_PixelAsPoint
 
 Introduction: Returns a point geometry of the specified pixel's upper-left corner. The pixel coordinates specified are 1-indexed.