ncquiverref

Quiver (vector) with a reference vector or color code on a map or Cartesian axes.

Description

This function is a substitute for the standard versions of quiver and quiverm available using a vanilla release of matlab. This version assumes a 2D vector field is being plotted using a gridded flow field from a numerical model. It is primarily intended for Earth System Model analysis.

The function enables the scaling of vectors according to a reference vector plotted in the lower right hand corner of the plot axes. The function works for both map and Cartesian axes and allows the color of vectors to be changed.

If a reference value is not provided, the reference value is calculated by rounding the median or maximum magnitude of the quiver vectors. Scaling of vectors still occurs even if the reference vector plotting is switched off. This enables different subplots to share identical scaling so that the relative magnitude of vectors can be compared between subplots (provided they share the same grid).

The function also includes the ability to plot color vectors, all of equal length but color coded according to their magnitude. In this case, a colorbar is provided, complete with units, and no scaling vector is plotted.

Vectors are centered on the grid points they represent, rather than the tail of the arrow being positioned on the grid point as is the case for the vanila Matlab quiver and quiverm versions.

• Required Products: Mapping Toolbox
• MATLAB release: MATLAB 7.11 (2010b)

[Ibrahim M]

This is genius!

For it to work in multiple colors, you make sure your x and y are produced with/as meshgrid. Also specify your colors according to your choice of colorbar. Eg if your caxis ([15 30]) for SST, then you should have the function as:

ncquiverref(x,y,xx,yy, 'DegC','mean',0,'col',[15 20 25 30]);

Nice work Andrew!

Thank you very much for sharing!!

Ibrahim

[Jason Sippel]

 

[Jason Sippel]

Great code! After chatting with the author, I have found that the below addendum is useful for plotting a small subdomian of model output. This would be useful if, for example, you are tracking a tropical cyclone in a Lagrangian system with ilat,flat,ilon, and flon sampled from your model grid based on the number of grid points from the storm center.

If you don't do something similar to this, the physical size of the map frame on the screen may not match from one figure to the next.

Here's the code:

    tightmap
    xlim=get(gca,'xlim');
    ylim=get(gca,'ylim');
    
   cutfactor = 1.3;
   xcenter=mean(xlim);
   xoffset=diff(xlim)/2;
   ycenter=mean(ylim);
   yoffset=diff(ylim)/2;
   set(gca,'Xlim',[xcenter-cutfactor*xoffset xcenter+cutfactor*xoffset]);
   set(gca,'Ylim',[ycenter-cutfactor*yoffset ycenter+cutfactor*yoffset]);

[Chong Zhou]

Genius work! It gives amazing visualisation of large amount of vectors, which is common in the data post-processing in article image velocimetry (PIV). The author also improved the code to better adapt to the application in PIV, where 'axis ij' is a must to plot pixel coordinate.

Again, great work and I strongly suggest people using PIV try this code!

Many thanks!

[Hamed Babazadeh Babazadeh]

Great code, just a question,

how to scale vector field as it is in quiver command, the default size of vectors is too much for my application.

Thanks

[Andrew Roberts]

Hi Hamed,

If you have tested using "max" instead of "median" for reftype, or your color vectors are too long, it is easy to adjust the variable "scalelength" to a fraction of its current value in the code. Change line 186 to:
scalelength=X*min(mean(z1(~isnan(z1))),mean(z2(~isnan(z2))));
where 0<X<1.
The main reason you may have to make this manual adjustment is if your vector magnitudes are strongly negatively skewed.

cheers
Andrew

[Thibaut Leroy]

 

[Josh Jones]

 

[Cheryl Harrison]

Is there any way to get this to plot vectors over a pcolor plot? I can get the vectors on just fine, but as soon as I plot the reference vector it whites everything out. Modification ideas?