Matlab自带函数中不包含构造 quiver 函数注释过程，本文参照 matplotlib 中 quiverkey 函数，构造类似函数为 Matlab 中 quiver 矢量场进行标注。

quiverkey函数

首先看 matplotlib 中 quiverkey 如何定义的

quiverkey(*args, **kw)
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:

  *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.


Additional kwargs: hold = [True|False] overrides default hold state

可以看到主要参数有这么些个

1. quiver绘图指针
2. 图例位置 X, Y
3. 标注大小 U
4. 标注单位字符
5. 其他参数
   1）. 输入坐标 X, Y 单位
   2）. （文字）标注在图例哪个位置
   3）. 标注与图例相对距离
   4）. 标注字体颜色

使用方法：

对应Matlab函数也应该使用这么个流程

1. 使用quiver绘图
2. 将quiver返回指针与图例位置坐标和大小等作为参数传入

示例

[x,y] = meshgrid(0:0.2:2,0:0.2:2);
u = cos(x).*y;
v = sin(x).*y;

figure; 
Qh = quiver(x,y,u,v);

quiverkey(Qh, 0.5, 2.5, 1, \'m/s\', \'Color\', \'r\', \'Coordinates\', \'data\')

最终效果图

代码

function Q = quiverkey(Q, X, Y, U, label, varargin)
%QUIVERKEY legend for quiver
%
%   QUIVERKEY(Q, X, Y, U, label) 
%   
%   Arguments:
%       Q :      The quiver handle returned by a call to quiver
%       X,Y :    The location of the legend
%       U :      The unit length. If U<0, the arrow will be reversed
%       label :  The string with the length and units of the key
%   
%   Addition arguments:
%       Coordinates = [ \'axes\' | \'data\'(default) ]
% 
%           \'axes\' & \'figure\' : \'axes\' and \'figure\' are normalized 
%                       coordinate systems with 0,0 in the lower left 
%                       and 1,1 in the upper right;
%           \'data\' :    use the axes data coordinates
% 
%       LabelDistance : Distance in \'coordinates\' between the arrow and the
%                   label. Deauft is 0.1 (units \'axes\').
% 
%       Color : overrides face and edge colors from Q.
% 
%       LabelPosition = [ \'N\' | \'S\'(default) | \'E\' | \'W\' ]
% 
%               Position the label above, below, to the right, 
%               to the left of the arrow, respectively.
% 
%       LabelColor : defaults to black
%       
%   Examples: 
% 
%   [x,y] = meshgrid(0:0.2:2,0:0.2:2);
%   u = cos(x).*y;
%   v = sin(x).*y;
%   figure; Qh = quiver(x,y,u,v);
%   quiverkey(Qh, 0.5, 2.5, 1, \'m/s\', \'Color\', \'r\', \'Coordinates\', \'data\')
%   
% Author:
%   li12242 - Department of Civil Engineering in Tianjin University
% Email:
%   li12242@tju.edu.cn
% 

%% get input argument
if nargin < 5 
    error(\'Input arguments" Number incorrect!\')
end

if isempty(varargin) && mod(length(varargin), 2) ~= 0
    error(\'Input arguments donot pairs!\')
else
    [CoorUnit, LabelDist, Color, LabelPosition, LabelColor] = getInput(varargin);
end


%% add legend arrow

% get original data
xData = get(Q, \'XData\'); yData = get(Q, \'YData\');
uData = get(Q, \'UData\'); vData = get(Q, \'VData\');

% get axes properties
haxes = get(Q, \'Parent\');
xLim = get(haxes, \'XLim\'); yLim = get(haxes, \'YLim\');
NextPlot = get(haxes, \'NextPlot\');

% set axes properties
set(haxes, \'NextPlot\', \'add\')

if strcmp(CoorUnit, \'axes\')
    % position of legend arrow
    xa = xLim(1) + X*(xLim(2) - xLim(1));
    ya = yLim(1) + Y*(yLim(2) - yLim(1));
else
    xa = X; ya = Y;
end

% add legend arrow into data vector
xData = [xData(:); xa]; yData = [yData(:); ya];
uData = [uData(:); U];  vData = [vData(:); 0];

% reset data
set(Q, \'XData\', xData, \'YData\', yData, \'UData\', uData, \'VData\', vData);
set(Q, \'Color\', Color)

%% add text
dx = LabelDist*(xLim(2) - xLim(1));
dy = LabelDist*(yLim(2) - yLim(1));

% set position of label
switch LabelPosition
    case \'N\'
        xl = xa; yl = ya + dy;
    case \'S\'
        xl = xa; yl = ya - dy;
    case \'E\'
        xl = xa + dx; yl = ya;
    case \'W\'
        xl = xa - dx; yl = ya;
end% switch

th = text(xl, yl, [num2str(U), \' \', label]);
set(th, \'Color\', LabelColor);

% turn axes properties to original
set(haxes, \'NextPlot\', NextPlot)

end% func

%% sub function

function [CoorUnit, LabelDist, Color, LabelPosition, LabelColor] = getInput(varcell)
% Input:
%   varcell - cell variable
% Output:
% 
nargin = numel(varcell);

%% set default arguments

CoorUnit = \'data\';
LabelDist = 0.05; % units \'axes\'
Color = \'k\';
LabelPosition = \'S\';
LabelColor = \'k\';

%% get input arguments
contour = 1;
while contour < nargin
    switch varcell{contour}
        case \'Coordinates\'
            CoorUnit = varcell{contour+ 1};
        case \'LabelDistance\'
            LabelDist = varcell{contour+ 1};
        case \'Color\'
            Color = varcell{contour+ 1};
        case \'LabelPosition\'
            LabelPosition = varcell{contour+ 1};
        case \'LabelColor\'
            LabelColor = varcell{contour+ 1};
        otherwise
            error(\'Unknown input argument.\')
    end% switch
    contour = contour + 2;
end% while

end% fun