matplotlib.axes.Axes.barbs

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

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 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:

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

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 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	float or None
animated	bool
antialiased or antialiaseds	Boolean or sequence of booleans
array	ndarray
capstyle	unknown
clim	a length 2 sequence of floats
clip_box	a Bbox instance
clip_on	bool
clip_path	[(Path, Transform) | Patch | None]
cmap	a colormap or registered colormap name
color	matplotlib color arg or sequence of rgba tuples
contains	a callable function
edgecolor or edgecolors	matplotlib color spec or sequence of specs
facecolor or facecolors	matplotlib color spec or sequence of specs
figure	a Figure instance
gid	an id string
hatch	[ ‘/’ | ‘' | ‘|’ | ‘-‘ | ‘+’ | ‘x’ | ‘o’ | ‘O’ | ‘.’ | ‘*’ ]
joinstyle	unknown
label	object
linestyle or dashes or linestyles	[‘solid’ | ‘dashed’, ‘dashdot’, ‘dotted’ | (offset, on-off-dash-seq) | '-' | '--' | '-.' | ':' | 'None' | ' ' | '']
linewidth or linewidths or lw	float or sequence of floats
norm	Normalize
offset_position	[ ‘screen’ | ‘data’ ]
offsets	float or sequence of floats
path_effects	AbstractPathEffect
picker	[None | bool | float | callable]
pickradius	float distance in points
rasterized	bool or None
sketch_params	(scale: float, length: float, randomness: float)
snap	bool or None
transform	Transform
url	a url string
urls	List[str] or None
visible	bool
zorder	float

Note

In addition to the above described arguments, this function can take a data keyword argument. If such a data argument is given, the following arguments are replaced by data[<arg>]:

• All positional and all keyword arguments.