Matlab矢量图图例函数quiverkey

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