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Polish coordinate system

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It's important to distinguish between pixels and points. A square set
of points belongs to one pixel. When users type `linewidth=3`, they
usually mean a line 3 pixels wide. The distance between the pixel
center points, then, is 2.
This commit is contained in:
Juan Nunez-Iglesias
2014-01-29 22:47:52 +11:00
parent 80dcc0cd7b
commit 00f4d38c2c
1 changed files with 15 additions and 5 deletions
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skimage/measure/profile.py
+15 -5
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@@ -40,27 +40,37 @@ def profile_line(img, src, dst, linewidth=1,
[1, 1, 1, 2, 2, 2],
[1, 1, 1, 2, 2, 2],
[0, 0, 0, 0, 0, 0]])
>>> profile_line(img, (2, 1), (2, 5))
>>> profile_line(img, (2, 1), (2, 4))
array([ 1., 1., 2., 2.])
Notes
-----
The destination point is included in the profile, in contrast to
standard numpy indexing.
"""
src_row, src_col = src = np.asarray(src, dtype=float)
dst_row, dst_col = dst = np.asarray(dst, dtype=float)
d_row, d_col = dst - src
theta = np.arctan2(d_row, d_col)
length = np.ceil(np.hypot(d_row, d_col))
length = np.ceil(np.hypot(d_row, d_col) + 1)
# we add one above because we include the last point in the profile
# (in contrast to standard numpy indexing)
line_col = np.linspace(src_col, dst_col, length)
line_row = np.linspace(src_row, dst_row, length)
# this if clause is necessary to keep the line centered on the true
# source and destination points. Otherwise, the computed line has
# an offset of `linewidth/2`
# an offset of `linewidth / 2`
if linewidth <= 1:
perp_lines = np.array([line_row[:, np.newaxis],
line_col[:, np.newaxis]])
else:
col_width = linewidth * np.sin(-theta) / 2
row_width = linewidth * np.cos(theta) / 2
# we subtract 1 from linewidth to change from pixel-counting
# (make this line 3 pixels wide) to point distances (the
# distance between pixel centers)
col_width = (linewidth - 1) * np.sin(-theta) / 2
row_width = (linewidth - 1) * np.cos(theta) / 2
perp_rows = np.array([np.linspace(row_i - row_width, row_i + row_width,
linewidth) for row_i in line_row])
perp_cols = np.array([np.linspace(col_i - col_width, col_i + col_width,