[英]Fitting a line to 2d points in MATLAB
I try to calculate a line that can fit given several points with 2-d coordinate in MATLAB. 我尝试计算一条线,该线可以在MATLAB中使用2维坐标给定多个点。 But the result is not I expected.
但是结果不是我预期的。 There may be something I understand wrong.
我可能理解有些错误。 Can anyone help me out?
谁能帮我吗? Thanks a lot.
非常感谢。 The code is as follows:
代码如下:
ptsAroundVCP_L=[180,188;177,191;174,191;171,191;168,188;] % points with 2-d coordinate
curLinePar_L=polyfit(ptsAroundVCP_L(:,2),ptsAroundVCP_L(:,1),1); % parameter of the fitted line
%% begin to plot
plotx=1:256;
figure(11);hold on;
plot(ptsAroundVCP_L(:,2),ptsAroundVCP_L(:,1),'sb');
ploty_L=polyval(curLinePar_L,plotx);
plot(plotx,ploty_L,'r');
hold off;
The output is shown as follows. 输出如下所示。 But what I expected is that the fitted line should go vertically in this case.
但是我期望的是,在这种情况下,拟合线应该垂直延伸。 I think there is something wrong with the line fitting.
我认为线路拟合有问题。
It is impossible to fit any reasonable polynomial to this data as given: 给出的数据不可能适合任何合理的多项式:
X Y
188 180
191 177
191 174
191 171
188 168
Take the transpose and you will get something reasonable: 进行移调,您将得到一些合理的信息:
ptsAroundVCP_L=[180,188;177,191;174,191;171,191;168,188;]
y = ptsAroundVCP_L(:,2);
x = ptsAroundVCP_L(:,1);
p = polyfit(x, y, 2);
plotx= linspace(150, 200, 101);
figure(11);
plot(x, y, 'sb');
hold on
ploty = polyval(p, plotx);
plot(plotx, ploty, '-');
hold off;
I think the problem is basically that you can't represent a vertical line in slope-intercept form. 我认为问题基本上是您无法以斜线截距形式表示垂直线。 If you flip x/y in your fit, you get the right result:
如果您按自己的要求翻转x / y,则会得到正确的结果:
ptsAroundVCP_L=[180,188;177,191;174,191;171,191;168,188;] % points with 2-d coordinate
curLinePar_L=polyfit(ptsAroundVCP_L(:,1),ptsAroundVCP_L(:,2),1); % parameter of the fitted line
%% begin to plot
plotx=168:180;
figure(11);hold on;
plot(ptsAroundVCP_L(:,1),ptsAroundVCP_L(:,2),'sb');
ploty_L=polyval(curLinePar_L,plotx);
plot(plotx,ploty_L,'r');
hold off;
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