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## Re: [Matplotlib-users] Artefacts in contour plot?

 Re: [Matplotlib-users] Artefacts in contour plot? From: John Hunter - 2005-01-17 21:53:37 ```>>>>> "Dominique" == Dominique Orban writes: Dominique> I notice some spurious zigzagging lines towards the top Dominique> of the plot. Any idea where those might be coming from? I don't get zigzag lines either. Try using replacing matplotlib.axes.Axes.contour with the function included below (from CVS) and let me know if it works. Dominique> Also, the figure produced by the above script is Dominique> flipped horizontally. The corresponding Matlab script Dominique> produces the correct plot. matplotlib supports two image / contour orientation styles, and this is controlled by an rc parameter. Try (note the origin kwarg) from matplotlib.pylab import * def rosenbrock(x,y): return 10.0 * (y-x**2)**2 + (x-1)**2 x = arange( -1.5, 1.5, 0.01 ) y = arange( -0.5, 1.5, 0.01 ) [X,Y] = meshgrid( x, y ) Z = rosenbrock( X, Y ) contour( Z, x=X, y=Y, levels = 50, origin='lower' ) show() Amended contour function def contour(self, z, x = None, y = None, levels = None, colors = None, linewidths = None, alpha = 1.0, fmt='%1.3f', origin=None): """\ CONTOUR(z, x = None, y = None, levels = None, colors = None) plots contour lines of an image z z is a 2D array of image values x and y are 2D arrays with coordinates of z values in the two directions. x and y do not need to be evenly spaced but must be of the same shape as z levels can be a list of level values or the number of levels to be plotted. If levels == None, a default number of 7 evenly spaced levels is plotted. colors is one of these: - a tuple of matplotlib color args (string, float, rgb, etc), different levels will be plotted in different colors in the order specified - one string color, e.g. colors = 'r' or colors = 'red', all levels will be plotted in this color - if colors == None, the default color for lines.color in .matplotlibrc is used. linewidths is one of: - a number - all levels will be plotted with this linewidth, e.g. linewidths = 0.6 - a tuple of numbers, e.g. linewidths = (0.4, 0.8, 1.2) different levels will be plotted with different linewidths in the order specified - if linewidths == None, the default width in lines.linewidth in .matplotlibrc is used reg is a 2D region number array with the same dimensions as x and y. The values of reg should be positive region numbers, and zero fro zones wich do not exist. triangle - triangulation array - must be the same shape as reg alpha : the default transparency of contour lines fmt is a format string for adding a label to each collection. Currently this is useful for auto-legending and may be useful down the road for legend labeling origin = 'upper'|'lower'|None. If None, the rc value for image.origin will be used More information on reg and triangle arrays is in _contour.c Return value is levels, collections where levels is a list of contour levels used and collections is a list of matplotlib.collections.LineCollection instances """ if origin is None: origin = rcParams['image.origin'] if origin == 'upper': if x is not None: x = x[::-1] if y is not None: y = y[::-1] z = z[::-1] if not self._hold: self.cla() if which[0] == "numeric": z = array(z.tolist(),typecode = z.typecode()) if len(shape(z)) != 2: raise TypeError("Input must be a 2D array.") else: jmax, imax = shape(z) region = 0 reg = ones((jmax,imax), Int32) reg[:,0]=0 triangle = zeros((jmax,imax), Int32) if x == None and y == None: y, x = indices((jmax,imax), 'd') rz = ravel(z) zmax = nxmax(rz) zmin = nxmin(rz) def autolev(N): return mlab.linspace(zmin, zmax, N+2)[1:-1] if levels is None: lev = autolev(7) else: try: Nlev = int(levels) except TypeError: lev = list(levels) else: lev = autolev(Nlev) Nlev = len(lev) if colors == None: colors = rcParams['lines.color'] if is_string_like(colors): colors = [colors] * Nlev elif iterable(colors) and len(colors) < Nlev: colors = list(colors) * Nlev else: try: gray = float(colors) except TypeError: pass else: colors = [gray] * Nlev tcolors = [] for c in colors: tcolors.append((colorConverter.to_rgba(c, alpha),)) if linewidths == None: tlinewidths = [linewidths] *Nlev else: if iterable(linewidths) and len(linewidths) < Nlev: linewidths = list(linewidths) * int(ceil(Nlev/len(linewidths))) elif not iterable(linewidths) and type(linewidths) in [int, float]: linewidths = [linewidths] * Nlev tlinewidths = [(w,) for w in linewidths] args = zip(lev, tcolors, tlinewidths) levels = [] collections = [] for level, color, width in args: ntotal, nparts = _contour.GcInit1(x, y, reg, triangle, region, z, level) np = zeros((nparts,), Int32) xp = zeros((ntotal, ), Float64) yp = zeros((ntotal,), Float64) nlist = _contour.GcTrace(np, xp, yp) col = LineCollection(nlist, colors=color, linewidths = width) col.set_label(fmt%level) self.add_collection(col) levels.append(level) #col.set_linestyle('dashdot') # dashed|dotted|solid|dashdot #dashes = 0, (4,2,8,1) #col.set_linestyle( (dashes,) ) # offset, onoffseq collections.append(col) if x is not None: rx = ravel(x) self.set_xlim((min(rx), max(rx))) else: self.set_xlim([0,imax]) if y is not None: ry = ravel(y) self.set_ylim((min(ry), max(ry))) else: self.set_ylim([0,jmax]) return levels, collections ```