matplotlib quiver箭图绘制案例
quiver绘制表示梯度变化非常有用,下面是学习过程中给出的两个例子,可以很好理解quiver的用法
from pylab import * close() ## example 1 x = linspace(0,10,40) y = x**2*exp(-x) u = array([x[i+1]-x[i] for i in range(len(x)-1)]) v = array([y[i+1]-y[i] for i in range(len(x)-1)]) x = x[:len(u)] # 使得维数和u,v一致 y = y[:len(v)] c = randn(len(u)) # arrow颜色 figure() quiver(x,y,u,v,c, angles='xy', scale_units='xy', scale=1) # 注意参数的赋值 ## example 2 x = linspace(0,20,30) y = sin(x) u = array([x[i+1]-x[i] for i in range(len(x)-1)]) v = array([y[i+1]-y[i] for i in range(len(x)-1)]) x = x[:len(u)] # 使得维数和u,v一致 y = y[:len(v)] c = randn(len(u)) # arrow颜色 figure() quiver(x,y,u,v,c, angles='xy', scale_units='xy', scale=1) # 注意参数的赋值 show()
结果如下:
补充知识: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
quiver绘图指针
图例位置 X, Y
标注大小 U
标注单位字符
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
使用quiver绘图
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
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