region module provides a polygon filling algorithm
skymatch to create data masks.
Polygon filling algorithm.
|Authors:||Nadezhda Dencheva, Mihai Cara (contact: email@example.com)|
Base class for regions.
Sets mask values to region id for all pixels within the region. Subclasses must define this method.
Parameters: mask (ndarray) – a byte array with the shape of the observation to be used as a mask Returns: mask – pixels which are not included in any region). Return type: array where the value of the elements is the region ID or 0 (for
Edge(name=None, start=None, stop=None, next=None)¶
An edge has a “start” and “stop” (x,y) vertices and an entry in the GET table of a polygon. The GET entry is a list of these values:
[ymax, x_at_ymin, delta_x/delta_y]
Compute the entry for an edge in the current Active Edge Table
[ymax, x_intersect, 1/m] note: currently 1/m is not used
Polygon(rid, vertices, coord_system='Cartesian')¶
Represents a 2D polygon region with multiple vertices
- rid (string) – polygon id
- vertices (list of (x,y) tuples or lists) – The list is ordered in such a way that when traversed in a counterclockwise direction, the enclosed area is the polygon. The last vertex must coincide with the first vertex, minimum 4 vertices are needed to define a triangle
- coord_system (string) – coordinate system
Create a list of Edge objects from vertices
This is the main function which scans the polygon and creates the mask
- data (array) – the mask array it has all zeros initially, elements within a region are set to the region’s ID
- Algorithm –
- Set the Global Edge Table (GET) (-) –
- Set y to be the smallest y coordinate that has an entry in GET (-) –
- Initialize the Active Edge Table (AET) to be empty (-) –
- For each scan line (-) –
- Add edges from GET to AET for which ymin==y
- Remove edges from AET fro which ymax==y
- Compute the intersection of the current scan line with all edges in the AET
- Sort on X of intersection point
- Set elements between pairs of X in the AET to the Edge’s ID
Update the Active Edge Table (AET)
Add edges from GET to AET for which ymin of the edge is equal to the y of the scan line. Remove edges from AET for which ymax of the edge is equal to y of the scan line.