matlab - quiver3 arrow color corresponding to magnitude -

i want color of each arrow in quiver3 plot matlab correspond magnitude of each arrow. there way that?

i saw few examples online able 2d quiver, none of them work 3d variant, quiver3.

i have following plot , want replace blue arrows color corresponding magnitude.

in old graphics system (r2014a , earlier) not possible using built-in quiver object. can of plot objects used compose quiver plot

q = quiver(1:5, 1:5, 1:5, 1:5); handles = findall(q, 'type', 'line'); 

but tails represented 1 plot object, , arrow heads represented another. such, can't alter color of each head/tail individually.

set(handles(1), 'color', 'r') set(handles(2), 'color', 'g') 

however, introduction of hg2 (r2014b , later), can access two (undocumented) linestrip objects (matlab.graphics.primitive.world.linestrip) (one represents heads , 1 represents tails). these accessible via hidden properties tail , head.

q = quiver(1, 1, 1, 1); headlinestrip = q.head; taillinestrip = q.tail; 

you can alter color properties of these objects make each arrow different color.

the basic idea

to this, first compute magnitude of quiver arrows (this works both quiver , quiver3)

mags = sqrt(sum(cat(2, q.udata(:), q.vdata(:), ...             reshape(q.wdata, numel(q.udata), [])).^2, 2)); 

then use current colormap map each magnitude rgb value. shortest arrow assigned lowest color on colormap , longest arrow assigned highest color on colormap. histcounts works great assigning each magnitude index can passed ind2rgb along colormap itself. have multiply 255 because need color rgb 8-bit integer.

% current colormap currentcolormap = colormap(gca);  % determine color make each arrow using colormap [~, ~, ind] = histcounts(mags, size(currentcolormap, 1));  % map colormap cmap = uint8(ind2rgb(ind(:), currentcolormap) * 255); 

the linestrip colordata property (when specified truecolor) needs have alpha channel (which set 255 meaning opaque).

cmap(:,:,4) = 255; 

at point can set colorbinding property interpolated rather object (to decouple quiver object) , set colordata property of both q.head , q.tail colors created above giving each arrow it's own color.

full solution

note: solution works both quiver , quiver3 , code not have adapted @ all.

%// create quiver3 (could 2d quiver)  x = 1:10; y = 1:10; [x,y] = meshgrid(x, y); z = zeros(size(x)); u = zeros(size(x)); v = zeros(size(x)); w = sqrt(x.^2 + y.^2);  q = quiver3(x, y, z, u, v, w);  %// compute magnitude of vectors mags = sqrt(sum(cat(2, q.udata(:), q.vdata(:), ...             reshape(q.wdata, numel(q.udata), [])).^2, 2));  %// current colormap currentcolormap = colormap(gca);  %// determine color make each arrow using colormap [~, ~, ind] = histcounts(mags, size(currentcolormap, 1));  %// map colormap rgb cmap = uint8(ind2rgb(ind(:), currentcolormap) * 255); cmap(:,:,4) = 255; cmap = permute(repmat(cmap, [1 3 1]), [2 1 3]);  %// repeat each color 3 times (using 1:3 below) because each arrow has 3 vertices set(q.head, ...     'colorbinding', 'interpolated', ...     'colordata', reshape(cmap(1:3,:,:), [], 4).');   %'  %// repeat each color 2 times (using 1:2 below) because each tail has 2 vertices set(q.tail, ...     'colorbinding', 'interpolated', ...     'colordata', reshape(cmap(1:2,:,:), [], 4).'); 

and applied 2d quiver object

if don't want scale arrows entire range of colormap use following call histcounts (instead of line above) map magnitudes using color limits of axes.

clims = num2cell(get(gca, 'clim')); [~, ~, ind] = histcounts(mags, linspace(clims{:}, size(currentcolormap, 1)));