Isolines/contour in matlab

Question

I want to make a contour plot of three variables.

x coordinate , y coordinate and speed

Then I wish to depict the velocity directions on same plot with quiver.

Code:

k=49;
        data_k=data(:,1)==k&sp>sp_ths;%filter data
        x=xcor(data_k);y=ycor(data_k);sp_k=sp(data_k);vx_k=vx(data_k);vy_k=vy(data_k);
        if contour_plot
            [Xq, Yq] = meshgrid(x,y); 
            Zq =griddata(x,y,sp_k,Xq,Yq); 
            contour(Xq,Yq,Zq,5)%,'ShowText','on');
        end
        hold on
        quiver(x, y, vx_k*5, vy_k*5, 0, 'k');

Output:

contour seems incorrect, I cant understand why though.

Data:

>> [x,y,vx_k,vy_k,sp_k]

ans =

   57.3030   61.6410    0.8965    0.4430    2.0000
   84.9540   -0.0559    0.9534    0.3017    2.0000
   80.3200    7.7009    0.9009    0.4339    2.0000
   76.6780  -35.6720    0.9391   -0.3437    2.0000
   61.4120   54.7280    0.3449    0.9386    2.0000
   70.9940   32.3250    0.7934    0.6088    2.0000
  -77.8030    4.8428   -0.9998   -0.0178    2.0000
  -39.4330   66.0040   -0.6452    0.7640    2.0000
  -41.1680  -70.1010   -0.9055   -0.4244    2.0000
   57.7840  -58.3810    0.9264   -0.3765    2.0000
  -70.2350   -8.8322   -0.9975    0.0712    2.0000
  -77.6940  -26.3810   -0.9676   -0.2525    2.0000
  -49.7200  -48.1560   -0.5801   -0.8145    2.0000
  -34.4620  -76.7420   -0.6990   -0.7151    2.0000
   68.3490   21.6690    0.9678   -0.2516    2.0000
   71.7360  -16.5990    0.9287   -0.3709    2.0000
   17.9180  -66.0220    0.5107   -0.8598    2.0000
  -57.2370  -55.8160   -0.9522   -0.3055    2.0000
   86.0120    5.7037    0.9336    0.3583    2.0000
   75.7290   16.6260    0.9946    0.1035    1.9114
  -78.2140    4.6192   -0.9969    0.0783    2.0000
   42.9320  -63.1170    0.5138   -0.8579    2.0000
  -56.5820   39.2650   -0.2098    0.9777    2.0000
  -18.2490   75.0340   -0.0854    0.9963    2.0000
   75.4960  -28.2940    0.8437   -0.5367    2.0000
  -17.6210   74.9380   -0.0340    0.9994    2.0000
  -10.9350  -79.1950   -0.3356   -0.9420    2.0000
  -16.2720   69.7160    0.2938    0.9559    2.0000
  -70.9780  -37.1290   -0.9887    0.1496    2.0000
   71.9370  -38.4470    0.8501   -0.5266    2.0000
   73.3310   -7.0563    0.9994    0.0341    2.0000
   83.7780   19.1370    0.8500    0.5268    2.0000
   -8.1897   79.2620    0.0479    0.9989    2.0000
   56.7250   62.4670    0.9049    0.4256    2.0000
   56.6710   62.1070    0.8763    0.4818    2.0000
   77.0110    9.7810    0.9787   -0.2053    2.0000
   56.3630   62.7070    0.9476    0.3195    2.0000
   84.0260    0.2988    0.9618    0.2737    2.0000
  -68.5600  -42.1320   -0.9822   -0.1880    2.0000
   55.5620   63.5370    0.6724    0.7402    2.0000
   19.3120  -67.2460    0.1840   -0.9829    2.0000
  -71.6530   28.4280   -0.9346    0.3558    2.0000
  -35.6610  -75.9520   -0.1767   -0.9843    2.0000
   33.1410  -75.3810   -0.1116   -0.9938    2.0000
   55.1580   56.8510    0.5865    0.8099    2.0000
   34.6410  -75.9710    0.3960   -0.9183    2.0000
   57.9810  -58.1830    0.8255   -0.5645    2.0000
   62.0610  -56.7770    0.8238   -0.5669    2.0000
   46.5930  -68.1200    0.9947   -0.1029    2.0000
   38.4250  -74.4980    0.3652   -0.9309    2.0000
  -46.0560  -67.3300   -0.3544   -0.9351    2.0000
   75.8290   18.4470    0.9997    0.0244    1.9114
   72.4200   31.8080    0.9841    0.1777    2.0000
   61.8330  -53.1870    0.9163   -0.4005    2.0000
  -62.1240  -25.1080   -0.6117   -0.7911    2.0000
   57.0410   62.0730    0.8391    0.5440    2.0000
   73.0400   -2.7887    0.9313    0.3643    2.0000
   39.0000  -73.7550    0.3970   -0.9178    2.0000
   81.8430  -20.8660    0.9697   -0.2443    2.0000
  -77.8410    4.7747   -0.9584    0.2853    2.0000

There is no data for anyone to work with. Please provide a [Minimal, Complete, and Verifiable](http://stackoverflow.com/help/mcve) example. — sco1, Sep 24 '15 at 13:24
@excaza I have added the filter data corresponding to `x=xcor(data_k);y=ycor(data_k);sp_k=sp(data_k);vx_k=vx(data_k);vy_k=vy(data_k);` Does this do the job? — Abhishek Bhatia, Sep 24 '15 at 13:26
It is very useful to know why someone downvoted your post, in particular if you give example code and comply with most of the standards for questions asked on SO, do you not think? — lhcgeneva, Sep 24 '15 at 14:19
Your `Zq` has a lot of `NaN` values. I think that could be causing problems in your plot. Why I get 5 seemingly random coloured line-bunches I do not know yet. Also, your `x,y` grid is not monotonically increasing, thus scrambling the axes completely. — Adriaan, Sep 24 '15 at 14:51
@Adriaan thanks for reply. What do you suggest. Are there better values so getting 3-d contour plots? — Abhishek Bhatia, Sep 24 '15 at 16:13

score 1 · Accepted Answer · edited May 23 '17 at 11:50

I hope I have the answer for you here: Drawing 3D contour from 3D data

For start, contour and contour3 plots are to represent scalar fields, not vector fields. For vector field You can use quiver and quiver3 plots.

Note that for Contours You need two M-vectors of x and y coordinates and one M-matrix of z data, where z(ii,jj) corresponds to x(ii) and y(jj), but for quiver you need M-vectors of coordinates and M-vectors of vector directions, where x(ii), y(ii), z(ii), u(ii), v(ii) and w(ii) represent one "arrow" in the plot.

It would me helpful to provide image how it should look like.

Isolines/contour in matlab

1 Answers1