#!/usr/bin/env python """ From: James Boyle <boyle5@llnl.gov> Subject: possible candidate for examples directory using fill To: John Hunter <jdhunter@nitace.bsd.uchicago.edu> Date: Tue, 8 Mar 2005 15:44:11 -0800 I often compare the output from two sensors and I am interested in the sign of the differences. I wrote the enclosed code for find the polygons of the positive and negative regions of the difference of two curves. It is written for simple-minded straightforwardness rather than speed or elegance. It is easy to fill in the two sets of polygons with contrasting colors. For efficiency one could use collections but my curves are such that fill is quick enough. The code uses a simple linear technique to find the crossover point, this too could be made more sophisticated if one desired. I have found this code to be very handy for the comparisons I perform - maybe someone else would find it useful. --Jim """ #!/usr/bin/env python from pylab import * def findZero(i,x,y1,y2): im1 = i-1 m1 = (y1[i] - y1[im1])/(x[i] - x[im1]) m2 = (y2[i] - y2[im1])/(x[i] - x[im1]) b1 = y1[im1] - m1*x[im1] b2 = y2[im1] - m2*x[im1] xZero = (b1 - b2)/(m2 - m1) yZero = m1*xZero + b1 return (xZero, yZero) def posNegFill(x,y1,y2): diff = y2 - y1 pos = [] neg = [] xx1 = [x[0]] xx2 = [x[0]] yy1 = [y1[0]] yy2 = [y2[0]] oldSign = (diff[0] < 0 ) npts = x.shape[0] for i in range(1,npts): newSign = (diff[i] < 0) if newSign != oldSign: xz,yz = findZero(i,x,y1,y2) xx1.append(xz) yy1.append(yz) xx2.reverse() xx1.extend(xx2) yy2.reverse() yy1.extend(yy2) if oldSign: neg.append( (xx1,yy1) ) else: pos.append( (xx1,yy1) ) xx1 = [xz,x[i]] xx2 = [xz,x[i]] yy1 = [yz,y1[i]] yy2 = [yz,y2[i]] oldSign = newSign else: xx1.append( x[i]) xx2.append( x[i]) yy1.append(y1[i]) yy2.append(y2[i]) if i == npts-1: xx2.reverse() xx1.extend(xx2) yy2.reverse() yy1.extend(yy2) if oldSign : neg.append( (xx1,yy1) ) else: pos.append( (xx1,yy1) ) return pos,neg x1 = arange(0, 2, 0.01) y1 = sin(2*pi*x1) y2 = sin(4*pi*x1) # find positive and negative polygons of difference pos,neg = posNegFill(x1,y1,y2) # positive y2 > y1 is blue for x,y in pos: p = fill(x,y,'b') # negative Y2 < y1 is red for x,y in neg: p = fill(x,y,'r') show()

Generated by Doxygen 1.6.0 Back to index