MATLAB: Plot line color - matlab

Question

I am trying to run the following function so that I can plot some points connected by a line, but the lines are not displaying in the color I want (white). I tried other colors as well, but the lines still won't show. I don't understand why. Can someone help?
function draw_constellations
figure
hold on
axis([0,100,0,100])
grid off
set(gcf,'color','k')
set(gca,'color','k')
axis square
while 1
[x,y,button] = ginput(1);
switch button
case 1 % left mouse
p = plot(x,y,'w-*');
case {'q','Q'} % on keyboard
break;
end
end

Answer 1

It is because x and y you used to plot are scalers. To plot lines, you will need to store all the x and y you get from ginput in vectors and plot the vectors:
[x,y,button] = ginput(1);
switch button
case 1 % left mouse
xs = [xs x];
ys = [ys y];
p = plot(xs,ys,'w-*');
% more code to go
end
However, if xs and ys are plotted everytime a new point is entered, you will have lines overlapping. To avoid this, we only plot the first point and update the p.XData and p.YData for new points:
if isempty(p)
p = plot(x,y,'w-*');
else
p.XData = xs;
p.YData = ys;
Full code:
figure
hold on
axis([0,100,0,100])
grid off
set(gcf,'color','k')
set(gca,'color','k')
axis square
xs = [];
ys = [];
p = [];
while 1
[x,y,button] = ginput(1);
switch button
case 1 % left mouse
xs = [xs x];
ys = [ys y];
if isempty(p)
p = plot(x,y,'w-*');
else
p.XData = xs;
p.YData = ys;
end
case {'q','Q'} % on keyboard
break;
end
end
Result:

Answer 2

You can use
plot(x,y,'*','color','blue') % plots in blue.
plot(x,y,'*','color',[.5 .4 .7]) % plots the RGB value [.5 .4 .7].
If you want lots of color names, you could use the rgb function to return the RGB values of just about any color. For example,
plot(x,y,'*','color',rgb('blood red'))
Further demonstration on how to change the default color order that you get when you plot lines without specifying the color:
Ever wonder how it plots blue first, then dark green, then red, then cyan, etc.? Ever want to change the default order so that it plots curves with the color order you want instead of the default color order, and without having to specify the color in every single call to plot()? If so, run the attached demo.
% Unless you specify the 'Color' property when you plot,
% plots are plotted according to the 'ColorOrder' property of the axes.
% This demo shows how you can change the default color order of plots.
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
clear; % Erase all existing variables.
workspace; % Make sure the workspace panel is showing.
fontSize = 18;
% Make 20 plots, with 25 data points in each plot.
numberOfDataSets = 20;
x = 1:25;
y = rand(numberOfDataSets, length(x));
% These y would all be on top of each other.
% Separate the plots vertically.
offsets = repmat((1:numberOfDataSets)', [1, length(x)]);
y = y + offsets;
% Get the initial set of default plot colors.
initialColorOrder = get(gca,'ColorOrder') % Initial
% See what the colors look like when plotted:
subplot(2, 1, 1);
plot(x,y, 'LineWidth', 3);
grid on;
caption = sprintf('%d plots with the Initial Default Color Order (Note the repeating colors)', numberOfDataSets);
title(caption, 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure.
% Give a name to the title bar.
set(gcf,'name','Image Analysis Demo','numbertitle','off')
choice = menu('Which ColorOrder do you want?', 'jet', 'random', 'hsv', 'hot', 'cool', 'spring', 'summer',...
'autumn', 'winter', 'lines', 'gray', 'bone', 'copper', 'pink');
% Make a new axes:
subplot(2, 1, 2);
% Create a new colormap that will define the new default color order property.
switch choice
case 1
newDefaultColors = jet(numberOfDataSets);
case 2
newDefaultColors = rand(numberOfDataSets, 3);
case 3
newDefaultColors = hsv(numberOfDataSets);
case 4
newDefaultColors = hot(numberOfDataSets);
case 5
newDefaultColors = cool(numberOfDataSets);
case 6
newDefaultColors = spring(numberOfDataSets);
case 7
newDefaultColors = summer(numberOfDataSets);
case 8
newDefaultColors = autumn(numberOfDataSets);
case 9
newDefaultColors = winter(numberOfDataSets);
case 10
newDefaultColors = lines(numberOfDataSets);
case 11
newDefaultColors = gray(numberOfDataSets);
case 12
newDefaultColors = bone(numberOfDataSets);
case 13
newDefaultColors = copper(numberOfDataSets);
otherwise
newDefaultColors = pink(numberOfDataSets);
end
% Note: You can build your own custom order if you want,
% just make up a array with numberOfDataSets rows and 3 columns
% where each element is in the range 0-1.
% Apply the new default colors to the current axes.
set(gca, 'ColorOrder', newDefaultColors, 'NextPlot', 'replacechildren');
% Now get the new set of default plot colors.
% Verify it changed by printing out the new default color set to the commandwindow.
newColorOrder = get(gca,'ColorOrder')
% Now plot the datasets with the changed default colors.
plot(x,y, 'LineWidth', 3);
grid on;
caption = sprintf('%d plots with the New Default Color Order', numberOfDataSets);
title(caption, 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
msgbox('Done with ColorOrder demo!');
Special thanks/credit goes to this.