Adding an image/chart as plot background

I've created a scatter plot from the results of a cone penetration test and I the points to be representented on a roberston chart just as in the figure below but I don't just know how to go about. In summary this is what I need

Vs what I presently have

This is the chart I will like to have as background

Thanks in advance

[Jonas]

can you give your data as attachment please, so we can plot the given data. your code so far would also be nice. do you have the lines of image 2 only as picture or also as data?

Answer 1

[DGM]

Here's one cheap way. You'll have to crop the image down.

[inpict map] = imread('robertson_cropped.png');
inpict = ind2rgb(inpict,map); % this is an indexed image.  it must be RGB
inpict = flipud(inpict); % need to flip the image

% some fake data
n = 50;
x = 9.9*rand(n,1)+0.1;
y = 999*rand(n,1);

% build the plot in log/log scale
scatter(x,y); hold on;
set(gca,'xscale','log','yscale','log');
xlim([0.1 10]);
ylim([1 1000]);

% insert the image
hi = image(inpict,'xdata',[-1 1],'ydata',[0 3]);
set(gca,'ydir','normal')
uistack(hi,'down') % move it beneath the scatter plot

If you would rather have the Robertson chart constructed from clean line objects, you'll have to build it from primitives. I don't see any ready-made tools for doing that. I'm not sure how these curves would be described mathematically, but if that's not known, you can use one of these images as a template and just transcribe it like so:

https://www.mathworks.com/matlabcentral/answers/1841583-converting-multiple-lines-into-separate-equations-from-jpeg

For example, you could use the attached SVG file to get the curve data:

% using the following FEX tools:
% https://www.mathworks.com/matlabcentral/fileexchange/72225-load-svg-into-your-matlab-code

% filename of manually-fit svg file
fname = 'robertsonchart.svg';

% data range from original image axis labels
% this is where the rectangle is drawn in the SVG
xrange = [-1 1];
yrange = [0 3]; % because this is semilog-scale

% spline discretization parameter [0 1]
coarseness = 0.01;

% get plot box geometry
str0 = fileread(fname);
str = regexp(str0,'((?<=<rect)(.*?)(?=\/>))','match');
pbx = regexp(str,'((?<=x=")(.*?)(?="))','match');
pby = regexp(str,'((?<=y=")(.*?)(?="))','match');
pbw = regexp(str,'((?<=width=")(.*?)(?="))','match');
pbh = regexp(str,'((?<=height=")(.*?)(?="))','match');
pbrect = [str2double(pbx{1}{1}) str2double(pby{1}{1}) ...
    str2double(pbw{1}{1}) str2double(pbh{1}{1})];

% get text locations (i used circles as markers)
str = regexp(str0,'((?<=<circle)(.*?)(?=\/>))','match');
cx = regexp(str,'((?<=cx=")(.*?)(?="))','match');
cy = regexp(str,'((?<=cy=")(.*?)(?="))','match');
cx = str2double([cx{:}]);
cy = str2double([cy{:}]);
% rescale to fit data range
cx = xrange(1) + diff(xrange)*(cx-pbrect(1))/pbrect(3);
cy = yrange(1) + diff(yrange)*(pbrect(4) - (cy-pbrect(2)))/pbrect(4);
cx = 10.^cx; % because this is logscale
cy = 10.^cy; % because this is logscale

% get coordinates representing the curve
S = loadsvg(fname,coarseness,false);

% if there are multiple paths you want to extract
% you'll need to do do the rescaling, etc for each element of S
for k = 1:numel(S) % there are multiple curves
    x = S{k}(:,1);
    y = S{k}(:,2);
    
    % rescale to fit data range
    x = xrange(1) + diff(xrange)*(x-pbrect(1))/pbrect(3);
    y = yrange(1) + diff(yrange)*(pbrect(4) - (y-pbrect(2)))/pbrect(4);
    x = 10.^x; % because this is logscale
    y = 10.^y; % because this is logscale
    
    % shove the prepared data back into S for later
    S{k} = [x y];
end

% plot each curve
for k = 1:numel(S)
    x = S{k}(:,1);
    y = S{k}(:,2);
    hll = loglog(x,y); hold on
end

% add text labels
for k = 1:numel(cx)
    ht = text(cx(k),cy(k),sprintf('%d',k));
end

grid on;
xlim(10.^xrange) % log scale
ylim(10.^yrange) % log scale

You could save the appropriate variables to a .mat file and then write a little function (attached) to generate the chart.

% some fake data
n = 50;
x = 9.9*rand(n,1)+0.1;
y = 999*rand(n,1);

% throw down the chart background
robertsonchart();

% build the plot in log/log scale
scatter(x,y);

That looks a lot better. Feel free to change the line and text properties in robertsonchart.m.

[Samuel Nkwindja]

Thanks alot