Changes between Version 152 and Version 153 of WKTRaster/SpecificationWorking03

Timestamp:

09/11/11 12:46:43 (13 years ago)

Author:

dustymugs

Comment:

—

WKTRaster/SpecificationWorking03

@@ -25 +25 @@
 
 '''ST_Intersects(raster, raster)'''[[BR]]
+
+This function uses the same tests as the two geometry version of ST_Intersects where tests see if two rasters overlap, touches or has one within the other.  If any condition is true, the two rasters intersect.
+
+For this description, the rasters are called A and B and the bands tested are assumed to be 1.
+
+Preliminary criteria before the real work begins:
+
+1. make sure that rasters A and B have the same SRID.  if not, return false.
+
+2. make sure that the convex hulls of A and B intersect.  if not, return false.
+
+Special case where a raster may be fully contained within another raster's cell (the entirety of A within a cell of B):
+
+1. using a 3x3 search pattern, test each selected cell's geopoint (excluding no data by default unless exclude_nodata_value = FALSE) of A to that of B for overlap.
+
+2. if a cell of A does overlap a cell of B, return true.
+
+3. if no cell of A overlaps with B, continue to additional testing
+
+Actual testing involves the use of calculating the intersection of grid lines between A and B
+
+1. Using A's columns and B's rows in a 3x3 search pattern, calculate the intersection point of each pair of grid lines.
+
+2. If intersection point doesn't exist or is outside the bounds of the end points comprising each grid line used, go back to step 1.
+
+3. If intersection point exists and within bounds, sample the area around the intersection point by offset the intersection point by a small amount (1/10th of the smaller scale of A and B) for 360 degrees starting from 00:00.  sampled points are 0, 45, 90, 135, 180, 225, 270 and 315 degrees.
+
+4. At each sample point, test to see if the geopoint has non-nodata (unless including nodata) values in both A and B.  if so, return true.
+
+5. At the same time as step 4, build an adjacency matrix for the intersection to see if two non-overlapping pixels from A and B touch.
+
+6. Once all sample points have been tested and no overlapping pixels found, the adjacency matrix is checked to see if any sampled pixel of A touched a sampled pixel of B.  If two pixels touched, return true.
+
+7. If after all the searching and testing, nothing intersects or touches, return false.
+
+A set of ST_Intersects functions:
+
+1. ST_Intersects(raster rastA, raster rastB, integer bandA DEFAULT NULL, integer bandB DEFAULT NULL) -> boolean 
+
+If bandA and bandB are NULL, only the convex hulls of the rasters will be tested.  If bandA or bandB are provided, both parameters must be provided and not NULL.
+
+2. ST_Intersects(raster rastA, integer bandA, raster rastB, integer bandB) -> boolean
+
+The ST_Intersects(raster, geometry) functions may need to be adapted to use ST_Intersects(raster, raster).  The difficulty will be for the functions to decide whether or not converting the raster to a geometry or converting the geometry to a raster is faster.
+
 '''ST_AsRaster(geometry, pixeltype, val, nodataval, ulx, uly, width, height, pixelsizex, pixelsizey, skewx, skewy) -> raster - done see below'''