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""" Support for plotting vector fields.
Presently this contains Quiver and Barb. Quiver plots an arrow in the direction of the vector, with the size of the arrow related to the magnitude of the vector.
Barbs are like quiver in that they point along a vector, but the magnitude of the vector is given schematically by the presence of barbs or flags on the barb.
This will also become a home for things such as standard deviation ellipses, which can and will be derived very easily from the Quiver code. """
Plot a 2-D field of arrows.
Call signatures::
quiver(U, V, **kw) quiver(U, V, C, **kw) quiver(X, Y, U, V, **kw) quiver(X, Y, U, V, C, **kw)
*U* and *V* are the arrow data, *X* and *Y* set the location of the arrows, and *C* sets the color of the arrows. These arguments may be 1-D or 2-D arrays or sequences.
If *X* and *Y* are absent, they will be generated as a uniform grid. If *U* and *V* are 2-D arrays and *X* and *Y* are 1-D, and if ``len(X)`` and ``len(Y)`` match the column and row dimensions of *U*, then *X* and *Y* will be expanded with :func:`numpy.meshgrid`.
The default settings auto-scales the length of the arrows to a reasonable size. To change this behavior see the *scale* and *scale_units* kwargs.
The defaults give a slightly swept-back arrow; to make the head a triangle, make *headaxislength* the same as *headlength*. To make the arrow more pointed, reduce *headwidth* or increase *headlength* and *headaxislength*. To make the head smaller relative to the shaft, scale down all the head parameters. You will probably do best to leave minshaft alone.
*linewidths* and *edgecolors* can be used to customize the arrow outlines.
Parameters ---------- X : 1D or 2D array, sequence, optional The x coordinates of the arrow locations Y : 1D or 2D array, sequence, optional The y coordinates of the arrow locations U : 1D or 2D array or masked array, sequence The x components of the arrow vectors V : 1D or 2D array or masked array, sequence The y components of the arrow vectors C : 1D or 2D array, sequence, optional The arrow colors units : [ 'width' | 'height' | 'dots' | 'inches' | 'x' | 'y' | 'xy' ] The arrow dimensions (except for *length*) are measured in multiples of this unit.
'width' or 'height': the width or height of the axis
'dots' or 'inches': pixels or inches, based on the figure dpi
'x', 'y', or 'xy': respectively *X*, *Y*, or :math:`\\sqrt{X^2 + Y^2}` in data units
The arrows scale differently depending on the units. For 'x' or 'y', the arrows get larger as one zooms in; for other units, the arrow size is independent of the zoom state. For 'width or 'height', the arrow size increases with the width and height of the axes, respectively, when the window is resized; for 'dots' or 'inches', resizing does not change the arrows. angles : [ 'uv' | 'xy' ], array, optional Method for determining the angle of the arrows. Default is 'uv'.
'uv': the arrow axis aspect ratio is 1 so that if *U*==*V* the orientation of the arrow on the plot is 45 degrees counter-clockwise from the horizontal axis (positive to the right).
'xy': arrows point from (x,y) to (x+u, y+v). Use this for plotting a gradient field, for example.
Alternatively, arbitrary angles may be specified as an array of values in degrees, counter-clockwise from the horizontal axis.
Note: inverting a data axis will correspondingly invert the arrows only with ``angles='xy'``. scale : None, float, optional Number of data units per arrow length unit, e.g., m/s per plot width; a smaller scale parameter makes the arrow longer. Default is *None*.
If *None*, a simple autoscaling algorithm is used, based on the average vector length and the number of vectors. The arrow length unit is given by the *scale_units* parameter scale_units : [ 'width' | 'height' | 'dots' | 'inches' | 'x' | 'y' | 'xy' ], \ None, optional If the *scale* kwarg is *None*, the arrow length unit. Default is *None*.
e.g. *scale_units* is 'inches', *scale* is 2.0, and ``(u,v) = (1,0)``, then the vector will be 0.5 inches long.
If *scale_units* is 'width'/'height', then the vector will be half the width/height of the axes.
If *scale_units* is 'x' then the vector will be 0.5 x-axis units. To plot vectors in the x-y plane, with u and v having the same units as x and y, use ``angles='xy', scale_units='xy', scale=1``. width : scalar, optional Shaft width in arrow units; default depends on choice of units, above, and number of vectors; a typical starting value is about 0.005 times the width of the plot. headwidth : scalar, optional Head width as multiple of shaft width, default is 3 headlength : scalar, optional Head length as multiple of shaft width, default is 5 headaxislength : scalar, optional Head length at shaft intersection, default is 4.5 minshaft : scalar, optional Length below which arrow scales, in units of head length. Do not set this to less than 1, or small arrows will look terrible! Default is 1 minlength : scalar, optional Minimum length as a multiple of shaft width; if an arrow length is less than this, plot a dot (hexagon) of this diameter instead. Default is 1. pivot : [ 'tail' | 'mid' | 'middle' | 'tip' ], optional The part of the arrow that is at the grid point; the arrow rotates about this point, hence the name *pivot*. color : [ color | color sequence ], optional This is a synonym for the :class:`~matplotlib.collections.PolyCollection` facecolor kwarg. If *C* has been set, *color* has no effect.
Notes ----- Additional :class:`~matplotlib.collections.PolyCollection` keyword arguments:
%(PolyCollection)s
See Also -------- quiverkey : Add a key to a quiver plot """ % docstring.interpd.params
Add a key to a quiver plot.
Call signature::
quiverkey(Q, X, Y, U, label, **kw)
Arguments:
*Q*: The Quiver instance returned by a call to quiver.
*X*, *Y*: The location of the key; additional explanation follows.
*U*: The length of the key
*label*: A string with the length and units of the key
Keyword arguments:
*angle* = 0 The angle of the key arrow. Measured in degrees anti-clockwise from the x-axis.
*coordinates* = [ 'axes' | 'figure' | 'data' | 'inches' ] Coordinate system and units for *X*, *Y*: 'axes' and 'figure' are normalized coordinate systems with 0,0 in the lower left and 1,1 in the upper right; 'data' are the axes data coordinates (used for the locations of the vectors in the quiver plot itself); 'inches' is position in the figure in inches, with 0,0 at the lower left corner.
*color*: overrides face and edge colors from *Q*.
*labelpos* = [ 'N' | 'S' | 'E' | 'W' ] Position the label above, below, to the right, to the left of the arrow, respectively.
*labelsep*: Distance in inches between the arrow and the label. Default is 0.1
*labelcolor*: defaults to default :class:`~matplotlib.text.Text` color.
*fontproperties*: A dictionary with keyword arguments accepted by the :class:`~matplotlib.font_manager.FontProperties` initializer: *family*, *style*, *variant*, *size*, *weight*
Any additional keyword arguments are used to override vector properties taken from *Q*.
The positioning of the key depends on *X*, *Y*, *coordinates*, and *labelpos*. If *labelpos* is 'N' or 'S', *X*, *Y* give the position of the middle of the key arrow. If *labelpos* is 'E', *X*, *Y* positions the head, and if *labelpos* is 'W', *X*, *Y* positions the tail; in either of these two cases, *X*, *Y* is somewhere in the middle of the arrow+label key object. """
""" Labelled arrow for use as a quiver plot scale key."""
*, angle=0, coordinates='axes', color=None, labelsep=0.1, labelpos='N', labelcolor=None, fontproperties=None, **kw): martist.Artist.__init__(self) self.Q = Q self.X = X self.Y = Y self.U = U self.angle = angle self.coord = coordinates self.color = color self.label = label self._labelsep_inches = labelsep self.labelsep = (self._labelsep_inches * Q.ax.figure.dpi)
# try to prevent closure over the real self weak_self = weakref.ref(self)
def on_dpi_change(fig): self_weakref = weak_self() if self_weakref is not None: self_weakref.labelsep = (self_weakref._labelsep_inches*fig.dpi) self_weakref._initialized = False # simple brute force update # works because _init is # called at the start of # draw.
self._cid = Q.ax.figure.callbacks.connect('dpi_changed', on_dpi_change)
self.labelpos = labelpos self.labelcolor = labelcolor self.fontproperties = fontproperties or dict() self.kw = kw _fp = self.fontproperties # boxprops = dict(facecolor='red') self.text = mtext.Text( text=label, # bbox=boxprops, horizontalalignment=self.halign[self.labelpos], verticalalignment=self.valign[self.labelpos], fontproperties=font_manager.FontProperties(**_fp))
if self.labelcolor is not None: self.text.set_color(self.labelcolor) self._initialized = False self.zorder = Q.zorder + 0.1
""" Overload the remove method """ self.Q.ax.figure.callbacks.disconnect(self._cid) self._cid = None # pass the remove call up the stack martist.Artist.remove(self)
if True: # not self._initialized: if not self.Q._initialized: self.Q._init() self._set_transform() _pivot = self.Q.pivot self.Q.pivot = self.pivot[self.labelpos] # Hack: save and restore the Umask _mask = self.Q.Umask self.Q.Umask = ma.nomask self.verts = self.Q._make_verts(np.array([self.U]), np.zeros((1,)), self.angle) self.Q.Umask = _mask self.Q.pivot = _pivot kw = self.Q.polykw kw.update(self.kw) self.vector = mcollections.PolyCollection( self.verts, offsets=[(self.X, self.Y)], transOffset=self.get_transform(), **kw) if self.color is not None: self.vector.set_color(self.color) self.vector.set_transform(self.Q.get_transform()) self.vector.set_figure(self.get_figure()) self._initialized = True
if self.labelpos == 'E': return x + self.labelsep elif self.labelpos == 'W': return x - self.labelsep else: return x
if self.labelpos == 'N': return y + self.labelsep elif self.labelpos == 'S': return y - self.labelsep else: return y
def draw(self, renderer): self._init() self.vector.draw(renderer) x, y = self.get_transform().transform_point((self.X, self.Y)) self.text.set_x(self._text_x(x)) self.text.set_y(self._text_y(y)) self.text.draw(renderer) self.stale = False
if self.coord == 'data': self.set_transform(self.Q.ax.transData) elif self.coord == 'axes': self.set_transform(self.Q.ax.transAxes) elif self.coord == 'figure': self.set_transform(self.Q.ax.figure.transFigure) elif self.coord == 'inches': self.set_transform(self.Q.ax.figure.dpi_scale_trans) else: raise ValueError('unrecognized coordinates')
martist.Artist.set_figure(self, fig) self.text.set_figure(fig)
# Maybe the dictionary should allow one to # distinguish between a text hit and a vector hit. if (self.text.contains(mouseevent)[0] or self.vector.contains(mouseevent)[0]): return True, {} return False, {}
# This is a helper function that parses out the various combination of # arguments for doing colored vector plots. Pulling it out here # allows both Quiver and Barbs to use it X, Y, U, V, C = [None] * 5 args = list(args)
# The use of atleast_1d allows for handling scalar arguments while also # keeping masked arrays if len(args) == 3 or len(args) == 5: C = np.atleast_1d(args.pop(-1)) V = np.atleast_1d(args.pop(-1)) U = np.atleast_1d(args.pop(-1)) if U.ndim == 1: nr, nc = 1, U.shape[0] else: nr, nc = U.shape if len(args) == 2: # remaining after removing U,V,C X, Y = [np.array(a).ravel() for a in args] if len(X) == nc and len(Y) == nr: X, Y = [a.ravel() for a in np.meshgrid(X, Y)] else: indexgrid = np.meshgrid(np.arange(nc), np.arange(nr)) X, Y = [np.ravel(a) for a in indexgrid] return X, Y, U, V, C
all_shapes = {a.shape for a in arrays} if len(all_shapes) != 1: raise ValueError('The shapes of the passed in arrays do not match')
""" Specialized PolyCollection for arrows.
The only API method is set_UVC(), which can be used to change the size, orientation, and color of the arrows; their locations are fixed when the class is instantiated. Possibly this method will be useful in animations.
Much of the work in this class is done in the draw() method so that as much information as possible is available about the plot. In subsequent draw() calls, recalculation is limited to things that might have changed, so there should be no performance penalty from putting the calculations in the draw() method. """
scale=None, headwidth=3, headlength=5, headaxislength=4.5, minshaft=1, minlength=1, units='width', scale_units=None, angles='uv', width=None, color='k', pivot='tail', **kw): """ The constructor takes one required argument, an Axes instance, followed by the args and kwargs described by the following pyplot interface documentation: %s """ self.ax = ax X, Y, U, V, C = _parse_args(*args) self.X = X self.Y = Y self.XY = np.column_stack((X, Y)) self.N = len(X) self.scale = scale self.headwidth = headwidth self.headlength = float(headlength) self.headaxislength = headaxislength self.minshaft = minshaft self.minlength = minlength self.units = units self.scale_units = scale_units self.angles = angles self.width = width self.color = color
if pivot.lower() == 'mid': pivot = 'middle' self.pivot = pivot.lower() if self.pivot not in self._PIVOT_VALS: raise ValueError( 'pivot must be one of {keys}, you passed {inp}'.format( keys=self._PIVOT_VALS, inp=pivot))
self.transform = kw.pop('transform', ax.transData) kw.setdefault('facecolors', self.color) kw.setdefault('linewidths', (0,)) mcollections.PolyCollection.__init__(self, [], offsets=self.XY, transOffset=self.transform, closed=False, **kw) self.polykw = kw self.set_UVC(U, V, C) self._initialized = False
self.keyvec = None self.keytext = None
# try to prevent closure over the real self weak_self = weakref.ref(self)
def on_dpi_change(fig): self_weakref = weak_self() if self_weakref is not None: self_weakref._new_UV = True # vertices depend on width, span # which in turn depend on dpi self_weakref._initialized = False # simple brute force update # works because _init is # called at the start of # draw.
self._cid = self.ax.figure.callbacks.connect('dpi_changed', on_dpi_change)
""" Overload the remove method """ # disconnect the call back self.ax.figure.callbacks.disconnect(self._cid) self._cid = None # pass the remove call up the stack mcollections.PolyCollection.remove(self)
""" Initialization delayed until first draw; allow time for axes setup. """ # It seems that there are not enough event notifications # available to have this work on an as-needed basis at present. if True: # not self._initialized: trans = self._set_transform() ax = self.ax sx, sy = trans.inverted().transform_point( (ax.bbox.width, ax.bbox.height)) self.span = sx if self.width is None: sn = np.clip(math.sqrt(self.N), 8, 25) self.width = 0.06 * self.span / sn
# _make_verts sets self.scale if not already specified if not self._initialized and self.scale is None: self._make_verts(self.U, self.V, self.angles)
self._initialized = True
trans = self.get_transform() transOffset = self.get_offset_transform() full_transform = (trans - transData) + (transOffset - transData) XY = full_transform.transform(self.XY) bbox = transforms.Bbox.null() bbox.update_from_data_xy(XY, ignore=True) return bbox
def draw(self, renderer): self._init() verts = self._make_verts(self.U, self.V, self.angles) self.set_verts(verts, closed=False) self._new_UV = False mcollections.PolyCollection.draw(self, renderer) self.stale = False
# We need to ensure we have a copy, not a reference # to an array that might change before draw(). U = ma.masked_invalid(U, copy=True).ravel() V = ma.masked_invalid(V, copy=True).ravel() mask = ma.mask_or(U.mask, V.mask, copy=False, shrink=True) if C is not None: C = ma.masked_invalid(C, copy=True).ravel() mask = ma.mask_or(mask, C.mask, copy=False, shrink=True) if mask is ma.nomask: C = C.filled() else: C = ma.array(C, mask=mask, copy=False) self.U = U.filled(1) self.V = V.filled(1) self.Umask = mask if C is not None: self.set_array(C) self._new_UV = True self.stale = True
""" Return a scale factor for converting from units to pixels """ ax = self.ax if units in ('x', 'y', 'xy'): if units == 'x': dx0 = ax.viewLim.width dx1 = ax.bbox.width elif units == 'y': dx0 = ax.viewLim.height dx1 = ax.bbox.height else: # 'xy' is assumed dxx0 = ax.viewLim.width dxx1 = ax.bbox.width dyy0 = ax.viewLim.height dyy1 = ax.bbox.height dx1 = np.hypot(dxx1, dyy1) dx0 = np.hypot(dxx0, dyy0) dx = dx1 / dx0 else: if units == 'width': dx = ax.bbox.width elif units == 'height': dx = ax.bbox.height elif units == 'dots': dx = 1.0 elif units == 'inches': dx = ax.figure.dpi else: raise ValueError('unrecognized units') return dx
""" Sets the PolygonCollection transform to go from arrow width units to pixels. """ dx = self._dots_per_unit(self.units) self._trans_scale = dx # pixels per arrow width unit trans = transforms.Affine2D().scale(dx) self.set_transform(trans) return trans
xy = self.ax.transData.transform(self.XY) uv = np.column_stack((U, V)) xyp = self.ax.transData.transform(self.XY + eps * uv) dxy = xyp - xy angles = np.arctan2(dxy[:, 1], dxy[:, 0]) lengths = np.hypot(*dxy.T) / eps return angles, lengths
uv = (U + V * 1j) str_angles = angles if isinstance(angles, str) else '' if str_angles == 'xy' and self.scale_units == 'xy': # Here eps is 1 so that if we get U, V by diffing # the X, Y arrays, the vectors will connect the # points, regardless of the axis scaling (including log). angles, lengths = self._angles_lengths(U, V, eps=1) elif str_angles == 'xy' or self.scale_units == 'xy': # Calculate eps based on the extents of the plot # so that we don't end up with roundoff error from # adding a small number to a large. eps = np.abs(self.ax.dataLim.extents).max() * 0.001 angles, lengths = self._angles_lengths(U, V, eps=eps) if str_angles and self.scale_units == 'xy': a = lengths else: a = np.abs(uv) if self.scale is None: sn = max(10, math.sqrt(self.N)) if self.Umask is not ma.nomask: amean = a[~self.Umask].mean() else: amean = a.mean() # crude auto-scaling # scale is typical arrow length as a multiple of the arrow width scale = 1.8 * amean * sn / self.span if self.scale_units is None: if self.scale is None: self.scale = scale widthu_per_lenu = 1.0 else: if self.scale_units == 'xy': dx = 1 else: dx = self._dots_per_unit(self.scale_units) widthu_per_lenu = dx / self._trans_scale if self.scale is None: self.scale = scale * widthu_per_lenu length = a * (widthu_per_lenu / (self.scale * self.width)) X, Y = self._h_arrows(length) if str_angles == 'xy': theta = angles elif str_angles == 'uv': theta = np.angle(uv) else: theta = ma.masked_invalid(np.deg2rad(angles)).filled(0) theta = theta.reshape((-1, 1)) # for broadcasting xy = (X + Y * 1j) * np.exp(1j * theta) * self.width XY = np.stack((xy.real, xy.imag), axis=2) if self.Umask is not ma.nomask: XY = ma.array(XY) XY[self.Umask] = ma.masked # This might be handled more efficiently with nans, given # that nans will end up in the paths anyway.
return XY
""" length is in arrow width units """ # It might be possible to streamline the code # and speed it up a bit by using complex (x,y) # instead of separate arrays; but any gain would be slight. minsh = self.minshaft * self.headlength N = len(length) length = length.reshape(N, 1) # This number is chosen based on when pixel values overflow in Agg # causing rendering errors # length = np.minimum(length, 2 ** 16) np.clip(length, 0, 2 ** 16, out=length) # x, y: normal horizontal arrow x = np.array([0, -self.headaxislength, -self.headlength, 0], np.float64) x = x + np.array([0, 1, 1, 1]) * length y = 0.5 * np.array([1, 1, self.headwidth, 0], np.float64) y = np.repeat(y[np.newaxis, :], N, axis=0) # x0, y0: arrow without shaft, for short vectors x0 = np.array([0, minsh - self.headaxislength, minsh - self.headlength, minsh], np.float64) y0 = 0.5 * np.array([1, 1, self.headwidth, 0], np.float64) ii = [0, 1, 2, 3, 2, 1, 0, 0] X = x.take(ii, 1) Y = y.take(ii, 1) Y[:, 3:-1] *= -1 X0 = x0.take(ii) Y0 = y0.take(ii) Y0[3:-1] *= -1 shrink = length / minsh if minsh != 0. else 0. X0 = shrink * X0[np.newaxis, :] Y0 = shrink * Y0[np.newaxis, :] short = np.repeat(length < minsh, 8, axis=1) # Now select X0, Y0 if short, otherwise X, Y np.copyto(X, X0, where=short) np.copyto(Y, Y0, where=short) if self.pivot == 'middle': X -= 0.5 * X[:, 3, np.newaxis] elif self.pivot == 'tip': X = X - X[:, 3, np.newaxis] # numpy bug? using -= does not # work here unless we multiply # by a float first, as with 'mid'. elif self.pivot != 'tail': raise ValueError(("Quiver.pivot must have value in {{'middle', " "'tip', 'tail'}} not {0}").format(self.pivot))
tooshort = length < self.minlength if tooshort.any(): # Use a heptagonal dot: th = np.arange(0, 8, 1, np.float64) * (np.pi / 3.0) x1 = np.cos(th) * self.minlength * 0.5 y1 = np.sin(th) * self.minlength * 0.5 X1 = np.repeat(x1[np.newaxis, :], N, axis=0) Y1 = np.repeat(y1[np.newaxis, :], N, axis=0) tooshort = np.repeat(tooshort, 8, 1) np.copyto(X, X1, where=tooshort) np.copyto(Y, Y1, where=tooshort) # Mask handling is deferred to the caller, _make_verts. return X, Y
Plot a 2-D field of barbs.
Call signatures::
barb(U, V, **kw) barb(U, V, C, **kw) barb(X, Y, U, V, **kw) barb(X, Y, U, V, C, **kw)
Arguments:
*X*, *Y*: The x and y coordinates of the barb locations (default is head of barb; see *pivot* kwarg)
*U*, *V*: Give the x and y components of the barb shaft
*C*: An optional array used to map colors to the barbs
All arguments may be 1-D or 2-D arrays or sequences. If *X* and *Y* are absent, they will be generated as a uniform grid. If *U* and *V* are 2-D arrays but *X* and *Y* are 1-D, and if ``len(X)`` and ``len(Y)`` match the column and row dimensions of *U*, then *X* and *Y* will be expanded with :func:`numpy.meshgrid`.
*U*, *V*, *C* may be masked arrays, but masked *X*, *Y* are not supported at present.
Keyword arguments:
*length*: Length of the barb in points; the other parts of the barb are scaled against this. Default is 7.
*pivot*: [ 'tip' | 'middle' | float ] The part of the arrow that is at the grid point; the arrow rotates about this point, hence the name *pivot*. Default is 'tip'. Can also be a number, which shifts the start of the barb that many points from the origin.
*barbcolor*: [ color | color sequence ] Specifies the color all parts of the barb except any flags. This parameter is analogous to the *edgecolor* parameter for polygons, which can be used instead. However this parameter will override facecolor.
*flagcolor*: [ color | color sequence ] Specifies the color of any flags on the barb. This parameter is analogous to the *facecolor* parameter for polygons, which can be used instead. However this parameter will override facecolor. If this is not set (and *C* has not either) then *flagcolor* will be set to match *barbcolor* so that the barb has a uniform color. If *C* has been set, *flagcolor* has no effect.
*sizes*: A dictionary of coefficients specifying the ratio of a given feature to the length of the barb. Only those values one wishes to override need to be included. These features include:
- 'spacing' - space between features (flags, full/half barbs)
- 'height' - height (distance from shaft to top) of a flag or full barb
- 'width' - width of a flag, twice the width of a full barb
- 'emptybarb' - radius of the circle used for low magnitudes
*fill_empty*: A flag on whether the empty barbs (circles) that are drawn should be filled with the flag color. If they are not filled, they will be drawn such that no color is applied to the center. Default is False
*rounding*: A flag to indicate whether the vector magnitude should be rounded when allocating barb components. If True, the magnitude is rounded to the nearest multiple of the half-barb increment. If False, the magnitude is simply truncated to the next lowest multiple. Default is True
*barb_increments*: A dictionary of increments specifying values to associate with different parts of the barb. Only those values one wishes to override need to be included.
- 'half' - half barbs (Default is 5)
- 'full' - full barbs (Default is 10)
- 'flag' - flags (default is 50)
*flip_barb*: Either a single boolean flag or an array of booleans. Single boolean indicates whether the lines and flags should point opposite to normal for all barbs. An array (which should be the same size as the other data arrays) indicates whether to flip for each individual barb. Normal behavior is for the barbs and lines to point right (comes from wind barbs having these features point towards low pressure in the Northern Hemisphere.) Default is False
Barbs are traditionally used in meteorology as a way to plot the speed and direction of wind observations, but can technically be used to plot any two dimensional vector quantity. As opposed to arrows, which give vector magnitude by the length of the arrow, the barbs give more quantitative information about the vector magnitude by putting slanted lines or a triangle for various increments in magnitude, as show schematically below::
: /\ \\ : / \ \\ : / \ \ \\ : / \ \ \\ : ------------------------------
.. note the double \\ at the end of each line to make the figure .. render correctly
The largest increment is given by a triangle (or "flag"). After those come full lines (barbs). The smallest increment is a half line. There is only, of course, ever at most 1 half line. If the magnitude is small and only needs a single half-line and no full lines or triangles, the half-line is offset from the end of the barb so that it can be easily distinguished from barbs with a single full line. The magnitude for the barb shown above would nominally be 65, using the standard increments of 50, 10, and 5.
linewidths and edgecolors can be used to customize the barb. Additional :class:`~matplotlib.collections.PolyCollection` keyword arguments:
%(PolyCollection)s """ % docstring.interpd.params
''' Specialized PolyCollection for barbs.
The only API method is :meth:`set_UVC`, which can be used to change the size, orientation, and color of the arrows. Locations are changed using the :meth:`set_offsets` collection method. Possibly this method will be useful in animations.
There is one internal function :meth:`_find_tails` which finds exactly what should be put on the barb given the vector magnitude. From there :meth:`_make_barbs` is used to find the vertices of the polygon to represent the barb based on this information. ''' # This may be an abuse of polygons here to render what is essentially maybe # 1 triangle and a series of lines. It works fine as far as I can tell # however. pivot='tip', length=7, barbcolor=None, flagcolor=None, sizes=None, fill_empty=False, barb_increments=None, rounding=True, flip_barb=False, **kw): """ The constructor takes one required argument, an Axes instance, followed by the args and kwargs described by the following pyplot interface documentation: %(barbs_doc)s """ self.sizes = sizes or dict() self.fill_empty = fill_empty self.barb_increments = barb_increments or dict() self.rounding = rounding self.flip = flip_barb transform = kw.pop('transform', ax.transData) self._pivot = pivot self._length = length barbcolor = barbcolor flagcolor = flagcolor
# Flagcolor and barbcolor provide convenience parameters for # setting the facecolor and edgecolor, respectively, of the barb # polygon. We also work here to make the flag the same color as the # rest of the barb by default
if None in (barbcolor, flagcolor): kw['edgecolors'] = 'face' if flagcolor: kw['facecolors'] = flagcolor elif barbcolor: kw['facecolors'] = barbcolor else: # Set to facecolor passed in or default to black kw.setdefault('facecolors', 'k') else: kw['edgecolors'] = barbcolor kw['facecolors'] = flagcolor
# Explicitly set a line width if we're not given one, otherwise # polygons are not outlined and we get no barbs if 'linewidth' not in kw and 'lw' not in kw: kw['linewidth'] = 1
# Parse out the data arrays from the various configurations supported x, y, u, v, c = _parse_args(*args) self.x = x self.y = y xy = np.column_stack((x, y))
# Make a collection barb_size = self._length ** 2 / 4 # Empirically determined mcollections.PolyCollection.__init__(self, [], (barb_size,), offsets=xy, transOffset=transform, **kw) self.set_transform(transforms.IdentityTransform())
self.set_UVC(u, v, c)
''' Find how many of each of the tail pieces is necessary. Flag specifies the increment for a flag, barb for a full barb, and half for half a barb. Mag should be the magnitude of a vector (i.e., >= 0).
This returns a tuple of:
(*number of flags*, *number of barbs*, *half_flag*, *empty_flag*)
*half_flag* is a boolean whether half of a barb is needed, since there should only ever be one half on a given barb. *empty_flag* flag is an array of flags to easily tell if a barb is empty (too low to plot any barbs/flags. '''
# If rounding, round to the nearest multiple of half, the smallest # increment if rounding: mag = half * (mag / half + 0.5).astype(int)
num_flags = np.floor(mag / flag).astype(int) mag = np.mod(mag, flag)
num_barb = np.floor(mag / full).astype(int) mag = np.mod(mag, full)
half_flag = mag >= half empty_flag = ~(half_flag | (num_flags > 0) | (num_barb > 0))
return num_flags, num_barb, half_flag, empty_flag
pivot, sizes, fill_empty, flip): ''' This function actually creates the wind barbs. *u* and *v* are components of the vector in the *x* and *y* directions, respectively.
*nflags*, *nbarbs*, and *half_barb*, empty_flag* are, *respectively, the number of flags, number of barbs, flag for *half a barb, and flag for empty barb, ostensibly obtained *from :meth:`_find_tails`.
*length* is the length of the barb staff in points.
*pivot* specifies the point on the barb around which the entire barb should be rotated. Right now, valid options are 'tip' and 'middle'. Can also be a number, which shifts the start of the barb that many points from the origin.
*sizes* is a dictionary of coefficients specifying the ratio of a given feature to the length of the barb. These features include:
- *spacing*: space between features (flags, full/half barbs)
- *height*: distance from shaft of top of a flag or full barb
- *width* - width of a flag, twice the width of a full barb
- *emptybarb* - radius of the circle used for low magnitudes
*fill_empty* specifies whether the circle representing an empty barb should be filled or not (this changes the drawing of the polygon).
*flip* is a flag indicating whether the features should be flipped to the other side of the barb (useful for winds in the southern hemisphere).
This function returns list of arrays of vertices, defining a polygon for each of the wind barbs. These polygons have been rotated to properly align with the vector direction. '''
# These control the spacing and size of barb elements relative to the # length of the shaft spacing = length * sizes.get('spacing', 0.125) full_height = length * sizes.get('height', 0.4) full_width = length * sizes.get('width', 0.25) empty_rad = length * sizes.get('emptybarb', 0.15)
# Controls y point where to pivot the barb. pivot_points = dict(tip=0.0, middle=-length / 2.)
# Check for flip if flip: full_height = -full_height
endx = 0.0 try: endy = float(pivot) except ValueError: endy = pivot_points[pivot.lower()]
# Get the appropriate angle for the vector components. The offset is # due to the way the barb is initially drawn, going down the y-axis. # This makes sense in a meteorological mode of thinking since there 0 # degrees corresponds to north (the y-axis traditionally) angles = -(ma.arctan2(v, u) + np.pi / 2)
# Used for low magnitude. We just get the vertices, so if we make it # out here, it can be reused. The center set here should put the # center of the circle at the location(offset), rather than at the # same point as the barb pivot; this seems more sensible. circ = CirclePolygon((0, 0), radius=empty_rad).get_verts() if fill_empty: empty_barb = circ else: # If we don't want the empty one filled, we make a degenerate # polygon that wraps back over itself empty_barb = np.concatenate((circ, circ[::-1]))
barb_list = [] for index, angle in np.ndenumerate(angles): # If the vector magnitude is too weak to draw anything, plot an # empty circle instead if empty_flag[index]: # We can skip the transform since the circle has no preferred # orientation barb_list.append(empty_barb) continue
poly_verts = [(endx, endy)] offset = length
# Add vertices for each flag for i in range(nflags[index]): # The spacing that works for the barbs is a little to much for # the flags, but this only occurs when we have more than 1 # flag. if offset != length: offset += spacing / 2. poly_verts.extend( [[endx, endy + offset], [endx + full_height, endy - full_width / 2 + offset], [endx, endy - full_width + offset]])
offset -= full_width + spacing
# Add vertices for each barb. These really are lines, but works # great adding 3 vertices that basically pull the polygon out and # back down the line for i in range(nbarbs[index]): poly_verts.extend( [(endx, endy + offset), (endx + full_height, endy + offset + full_width / 2), (endx, endy + offset)])
offset -= spacing
# Add the vertices for half a barb, if needed if half_barb[index]: # If the half barb is the first on the staff, traditionally it # is offset from the end to make it easy to distinguish from a # barb with a full one if offset == length: poly_verts.append((endx, endy + offset)) offset -= 1.5 * spacing poly_verts.extend( [(endx, endy + offset), (endx + full_height / 2, endy + offset + full_width / 4), (endx, endy + offset)])
# Rotate the barb according the angle. Making the barb first and # then rotating it made the math for drawing the barb really easy. # Also, the transform framework makes doing the rotation simple. poly_verts = transforms.Affine2D().rotate(-angle).transform( poly_verts) barb_list.append(poly_verts)
return barb_list
self.u = ma.masked_invalid(U, copy=False).ravel() self.v = ma.masked_invalid(V, copy=False).ravel() if C is not None: c = ma.masked_invalid(C, copy=False).ravel() x, y, u, v, c = delete_masked_points(self.x.ravel(), self.y.ravel(), self.u, self.v, c) _check_consistent_shapes(x, y, u, v, c) else: x, y, u, v = delete_masked_points(self.x.ravel(), self.y.ravel(), self.u, self.v) _check_consistent_shapes(x, y, u, v)
magnitude = np.hypot(u, v) flags, barbs, halves, empty = self._find_tails(magnitude, self.rounding, **self.barb_increments)
# Get the vertices for each of the barbs
plot_barbs = self._make_barbs(u, v, flags, barbs, halves, empty, self._length, self._pivot, self.sizes, self.fill_empty, self.flip) self.set_verts(plot_barbs)
# Set the color array if C is not None: self.set_array(c)
# Update the offsets in case the masked data changed xy = np.column_stack((x, y)) self._offsets = xy self.stale = True
""" Set the offsets for the barb polygons. This saves the offsets passed in and actually sets version masked as appropriate for the existing U/V data. *offsets* should be a sequence.
Parameters ---------- offsets : sequence of pairs of floats """ self.x = xy[:, 0] self.y = xy[:, 1] x, y, u, v = delete_masked_points(self.x.ravel(), self.y.ravel(), self.u, self.v) _check_consistent_shapes(x, y, u, v) xy = np.column_stack((x, y)) mcollections.PolyCollection.set_offsets(self, xy) self.stale = True
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