I haven't checked the documentation, but I seem to recall that the images.roi tools need an image object in the given axes. It's the extent and resolution of the image object that defines the size of the generated mask and the relative position of the drawn object in the mask.
% Generate random 3D point cloud data
numPoints = 10;
x = rand(numPoints, 1);
y = rand(numPoints, 1);
z = rand(numPoints, 1);
% Plot the point cloud
scatter3(x, y, z, 'filled');
xlabel('X');
ylabel('Y');
zlabel('Z');
axis equal;
grid on;
hold on;
% put a dummy image in the xy plane
% some given number of pixels stretched over the axes area
hi = image(xlim,ylim,[100 100]);
hi.AlphaData = 0; % with zero opacity
% Create a freehand ROI
roi = drawline(gca);
That will allow you to use drawline(), although you're still only going to be working in the xy plane. Also, setting alpha may tend to make the ui very laggy if you're using software rendering. Again, setting the visibility property of the image object will also disable the ROI object.
