MATLAB: How to get/extract x,y values from scatter function

how to get/extract xMATLABy values from scatter function

Hi,

I am currently plotting the X,Y coordinates using scatter function as below.

scatter(x(:,1),x(:,2),[],x(:,3),'filled')

I would like to get the x,y value which is being plotted with different colors, could you please do help me out here.

thank you.

Best Answer

You need to apply thresholding to the 3rd column of the x variable upto blue colour as it is normalized colour. If you apply colourbar to the plot you can get idea how to choose threshold value

Demo:

>> x = rand(10, 2); % X, Y data
>> x(:, 3) = 1:10;  % colour data where 1 indicates complete blue, 2 - somewhat diluted colour so it is normalized
>> ax  = scatter(x(:,1),x(:,2),[],x(:,3),'filled');colorbar;

If you see the colorbar is the axes upto 5 level values are blue as you require, so get the values using CData properties of ax

>> x_values = ax.XData(ax.CData <5);
>> y_values = ax.YData(ax.CData <5);

Hope you get my point

Related Solutions

MATLAB: Convert point from color map / color bar to color vector

Background info

scatter & scatter3 use the axes' colormap along with the color axis limit (caxis|ax.CLim) to set the color of the markers.

To get the color of marker at index n, scale the scatter object's CData which contains the color scale value to the range of the colormap.

Solution

Use an anonymous function that receives an index value and returns the RGB vector associated with that data point. Set the colormap, color limit (caxis|ax.CLim) and the scatter object before creating the anonymous function.

ax = gca(); 
h = scatter3(___);
cmap  = ax.Colormap; 
clim = caxis(ax);
getRGB = @(i)cmap(round((h.CData(i)-clim(1))/range(clim) * (size(cmap,1)-1) + 1),:);  
% Example: Get RGB values for 4th data point in h

% getRGB(4)
%  ans = [0.2576 0.1814 0.7501]

Alternatively the axis and scatter handles could be included as inputs if you expect them to change.

getRGB = @(i,h,ax)ax.Colormap(round((h.CData(i)-ax.CLim(1))/range(ax.CLim) * (size(ax.Colormap,1)-1) + 1),:); 
% Example: Get RGB values for 4th data point in h
% getRGB(4,h,ax)
%  ans = [0.2576 0.1814 0.7501]

Demo

Circle markers are added to verify that their color matches the original data.

% Set up scatter3 plot
x = 0 : 0.1 : 10;
y = sin(x) + 1;
z = sin(y).^2;      %added '.'
point_size = 2*ones(size(x));
my_color = x;
h = scatter3(x,y,z, point_size, my_color); % added handle output
colorbar            % added
% Create a function to return the RGB value given an index value
ax = gca(); 
cmap  = ax.Colormap; 
clim = caxis(ax);
% create function: rgb = getRGB(i) 
% Create this after creating the scatter3 object, colormap, and color limits.  
getRGB = @(i)cmap(round((h.CData(i)-clim(1))/range(clim) * (size(cmap,1)-1) + 1),:);
% Test it by adding o markers around each point, matching colors
hold on
for i = 1:numel(h.XData)
    plot3(h.XData(i), h.YData(i), h.ZData(i), 'o','Color', getRGB(i))
end
●

MATLAB: How to retrieve the RGB data of a scatter plot from the CData values(a 1D vector corresponding to the array lengths X and Y)

You can obtain the indices based on the colormap and the Z vector applied to the CData property. Then you can get the corresponding RGB values using the "ind2rgb" function as follows:

h = scatter(x,y);
h.CData = z;
Cdata = h.CData;
cmap = colormap;
% make it into a index image.
cmin = min(Cdata(:));
cmax = max(Cdata(:));
m = length(cmap);
index = fix((Cdata-cmin)/(cmax-cmin)*m)+1; %A
% Then to RGB
RGB = ind2rgb(index,cmap)

For information on the "ind2rgb" function, refer this link:

http://www.mathworks.com/help/matlab/ref/ind2rgb.html

Best Answer

Related Solutions

MATLAB: Convert point from color map / color bar to color vector

MATLAB: How to retrieve the RGB data of a scatter plot from the CData values(a 1D vector corresponding to the array lengths X and Y)

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