source: cows/trunk/cows/bbox_util.py @ 4008

Subversion URL: http://proj.badc.rl.ac.uk/svn/ndg/cows/trunk/cows/bbox_util.py@4008
Revision 4008, 2.1 KB checked in by spascoe, 11 years ago (diff)

New COWS distribution. See [4005] for description.

Line 
1"""
2Utilities for manipulating bounding boxes as a tuple (llx, lly, urx, ury)
3
4@note: This has no connection with the cows data model.  This module
5    will probably move eventually.
6
7"""
8
9def intersection(bbox1, bbox2):
10    """
11    Return a bbox of the intersection of bbox1 and bbox2.
12
13    """
14    llx = max(bbox1[0], bbox2[0])
15    lly = max(bbox1[1], bbox2[1])
16    urx = min(bbox1[2], bbox2[2])
17    ury = min(bbox1[3], bbox2[3])
18
19    return llx, lly, urx, ury
20
21def relativeSize(bbox1, bbox2):
22    """
23    Calculate the relative size of bbox1 to bbox2.
24
25    @return: (sx, sy) where bbox1_width = sx * bbox2_width, etc.
26
27    """
28    sx = (bbox1[2]-bbox1[0]) / (bbox2[2]-bbox2[0])
29    sy = (bbox1[3]-bbox1[1]) / (bbox2[3]-bbox2[1])
30
31    return (sx, sy)
32
33def geoToPixel(x_g, y_g, bbox, width, height):
34    """
35    Calculate the pixel coordinate of a point within a bbox given the
36    width and height of the bbox in pixels.
37
38    This algorithm takes the origin of the bbox as the bottom left and
39    the origin of the image as top left.
40
41    @param x_g: x coordinate in goegraphic coordinates
42    @param y_g: y coordinate in geographic coordinates
43    @param bbox: The bounding box of the image
44    @param width: The width of the image in pixels
45    @param height: The height of the image in pixels.
46    @return: (x,y) in pixel coordinates
47
48    """
49
50    x = (x_g - bbox[0])*width / (bbox[2]-bbox[0])
51    y = (bbox[3] - y_g)*height / (bbox[3]-bbox[1])
52
53    return int(x), int(y)
54
55def pixelToGeo(x, y, bbox, width, height):
56    """
57    Calculate the geographic coordinates of a pixel on an image
58    of given bbox and size.
59
60    This algorithm takes the origin of the bbox as the bottom left and
61    the origin of the image as top left.
62
63    @param x: x coordinate in pixel coordinates
64    @param y: y coordinate in pixel coordinates
65    @param bbox: The bounding box of the image
66    @param width: The width of the image in pixels
67    @param height: The height of the image in pixels.
68   
69    @return: (x_g, y_g) in geographic coordinates
70   
71    """
72
73    x_g = bbox[0] + ((bbox[2]-bbox[0]) / width)*x   
74    y_g = bbox[3] - ((bbox[3]-bbox[1]) / height)*y
75
76    return (x_g, y_g)
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