On Monday 26 January 2009, Wayne Watson wrote: > the three def stmts below. Maybe someone can hazard a guess? It > looks like someone had fun doing this.
First bookmark this webpage. It explains every important function in Numpy: http://www.scipy.org/Numpy_Example_List_With_Doc > def Centroid( self, ref, curr, mask ): ref is maybe dark frame > slopes = indices((488,722),int32) > nada = zeros((488,722),uint8) > Do discrimination; areas that are not covered by the meteor are 0 > result = where(curr > ref, curr-ref, nada) > result = where(result > mask, result-mask, nada) > Compute center of mass http://en.wikipedia.org/wiki/Center_of_mass#Definition Look at first formula - result is m - slopes[1] is x-component of r - slopes[0] is y-component of r > xresult = result * slopes[1] > yresult = result * slopes[0] > total = sum(ravel(asarray(result,int32))) > count = sum(ravel(result > 0)) > if total == 0: > return 360,240,0,0 > > xpos = sum(ravel(xresult))/total > ypos = sum(ravel(yresult))/total > > return xpos,ypos,total,count Example algorithm done in Ipython invoked with ipython --pylab ---- In [20]:weights = array([0,0,1,1,1],'d') #These are three weights of mass 1. #They are located at the positions 2, 3, 4. #The center of gravity is therefore at position 3. In [21]:distances = indices(weights.shape) In [22]:distances Out[22]:array([[0, 1, 2, 3, 4]]) In [23]:moments = weights * distances In [24]:moments Out[24]:array([[ 0., 0., 2., 3., 4.]]) In [25]:tot_weight = sum(weights) In [26]:tot_moment = sum(moments) In [27]:center = tot_moment/tot_weight In [28]:center Out[28]:3.0 #Yay, this is the correct result! Kind regards, Eike. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
