matplotlib.axes.Axes.barbs

Axes.barbs(*args, data=None, **kw)[source]

Plot a 2D field of barbs.

Call signature:

barbs([X, Y], U, V, [C], **kw)

Where X, Y define the barb locations, U, V define the barb directions, and C optionally sets the color.

All arguments may be 1D or 2D. U, V, C may be masked arrays, but masked X, Y are not supported at present.

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:

:                   /\    \
:                  /  \    \
:                 /    \    \    \
:                /      \    \    \
:               ------------------------------

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.

See also https://en.wikipedia.org/wiki/Wind_barb.

Parameters:
X, Y1D or 2D array-like, optional

The x and y coordinates of the barb locations. See pivot for how the barbs are drawn to the x, y positions.

If not given, they will be generated as a uniform integer meshgrid based on the dimensions of U and V.

If X and Y are 1D but U, V are 2D, X, Y are expanded to 2D using X, Y = np.meshgrid(X, Y). In this case len(X) and len(Y) must match the column and row dimensions of U and V.

U, V1D or 2D array-like

The x and y components of the barb shaft.

C1D or 2D array-like, optional

Numeric data that defines the barb colors by colormapping via norm and cmap.

This does not support explicit colors. If you want to set colors directly, use barbcolor instead.

lengthfloat, default: 7

Length of the barb in points; the other parts of the barb are scaled against this.

pivot{'tip', 'middle'} or float, default: 'tip'

The part of the arrow that is anchored to the X, Y grid. The barb rotates about this point. This can also be a number, which shifts the start of the barb that many points away from grid point.

barbcolorcolor or color sequence

The color of all parts of the barb except for the flags. This parameter is analogous to the edgecolor parameter for polygons, which can be used instead. However this parameter will override facecolor.

flagcolorcolor or color sequence

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.

sizesdict, optional

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_emptybool, default: False

Whether the empty barbs (circles) that are drawn should be filled with the flag color. If they are not filled, the center is transparent.

roundingbool, default: True

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.

barb_incrementsdict, optional

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_barbbool or array-like of bool, default: False

Whether the lines and flags should point opposite to normal. 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).

A single value is applied to all barbs. Individual barbs can be flipped by passing a bool array of the same size as U and V.

Returns:
barbsBarbs
Other Parameters:
dataindexable object, optional

If given, all parameters also accept a string s, which is interpreted as data[s] (unless this raises an exception).

**kwargs

The barbs can further be customized using PolyCollection keyword arguments:

Property Description
agg_filter a filter function, which takes a (m, n, 3) float array and a dpi value, and returns a (m, n, 3) array
alpha array-like or scalar or None
animated bool
antialiased or aa or antialiaseds bool or list of bools
array array-like or None
capstyle CapStyle or {'butt', 'projecting', 'round'}
clim (vmin: float, vmax: float)
clip_box Bbox
clip_on bool
clip_path Patch or (Path, Transform) or None
cmap Colormap or str or None
color color or list of rgba tuples
contains unknown
edgecolor or ec or edgecolors color or list of colors or 'face'
facecolor or facecolors or fc color or list of colors
figure Figure
gid str
hatch {'/', '\', '|', '-', '+', 'x', 'o', 'O', '.', '*'}
in_layout bool
joinstyle JoinStyle or {'miter', 'round', 'bevel'}
label object
linestyle or dashes or linestyles or ls str or tuple or list thereof
linewidth or linewidths or lw float or list of floats
norm Normalize or None
offsets (N, 2) or (2,) array-like
path_effects AbstractPathEffect
paths list of array-like
picker None or bool or float or callable
pickradius float
rasterized bool
sizes ndarray or None
sketch_params (scale: float, length: float, randomness: float)
snap bool or None
transform Transform
url str
urls list of str or None
verts list of array-like
verts_and_codes unknown
visible bool
zorder float

Examples using matplotlib.axes.Axes.barbs