delaunay: reorganise example

delaunay_surf_example.m

@@ -1,65 +1,33 @@
-%% 2D interpolated image of "temperature" at N points
+%% 2D interpolated image of scattered data
+%
+% This example file first looks at regular interpolation using "gridded"
+% data. The second section shows how to plot regular scattered data using
+% triplot and Delaunay Triangulation. Finally, interpolation using
+% delaunay_surf shows what the code is all about.
+
+%% Some random data to plot
+%
+% This code assumes that you're trying to plot a 3D surface of values over
+% a set of non-uniform (x,y) data points.
 
-%% Gridded data:
-
-[x,y,z] = peaks(5);
-figure(98);
-subplot(3,3,1); cla; hold on
-surf(x,y,z);
-axis tight
-view(3)
-
-subplot(3,3,2); cla; hold on
-surf(x,y,z);
-view(2)
-
-subplot(3,3,3); cla; hold on
-p = surf(x,y,z);
-view(2)
-set(p,'edgecolor','none')
-
-subplot(3,3,4); cla; hold on
-p = surf(x,y,z);
-axis tight
-shading interp
-view(3)
-set(p,'EdgeColor','black','linewidth',0.1)% delete this line to remove the lines
-
-subplot(3,3,5); cla; hold on
-p = surf(x,y,z);
-shading interp
-view(2)
-set(p,'EdgeColor','black','linewidth',0.1)% delete this line to remove the lines
-
-subplot(3,3,6); cla; hold on
-p = surf(x,y,z);
-shading interp
-view(2)
-
-F = griddedInterpolant(x',y',z');
-[x2,y2] = ndgrid(linspace(-3,3,20));
-
-subplot(3,3,7); cla; hold on
-surf(x2,y2,F(x2,y2))
-view(3); axis tight
-
-subplot(3,3,8); cla; hold on
-surf(x2,y2,F(x2,y2))
-view(2);
+N = 15;
+rng(13);
+x = randn(1,N); % X & Y coords
+y = randn(1,N);
+z = randn(1,N); % "value" at each (x,y) coordinate
 
-subplot(3,3,9); cla; hold on
-p = surf(x2,y2,F(x2,y2));
-view(2);
-set(p,'edgecolor','none')
 
-%% Scattered data:
+%% Plotting scattered data
+%
+% This section shows how to plot scattered data using default Matlab commands.
+% The unshaded colourmapping is very poor at representing coarse grids, and
+% the interpolated shading shows edge artifacts where the surface changes quickly.
 
 N = 15;
-
 rng(13);
 x = randn(1,N); % X & Y coords
 y = randn(1,N);
-z = randn(1,N); % "temperatures" at each coordinate
+z = randn(1,N); % "value" at each (x,y) coordinate
 
 figure(99);
 subplot(2,2,1); cla; hold on
@@ -82,54 +50,122 @@
 shading interp
 view(2)
 
-%%
+
+%% Delaunay Interpolation
+%
+% This shows the basics of the interpolation. The midpoint of each Delaunay
+% triangle is used to calculate a new interpolated point.
+
+figure(102); clf; hold on
+
+p1 = delaunay_surf(x,y,z,'N',1);
+p2 = delaunay_surf(x,y,z,'N',0);
+set(p1,'facecolor','none','edgecolor','red')
+set(p2,'facecolor','none','linewidth',2)
+view(2)
+
+
+%% Three examples of interpolation.
+%
+% * The first shows the 3D surface with black edges to demonstrate the
+%   effect of the interpolation.
+%
+% * The second shows the same view from the top and without the edge lines;
+%   generally a better way to visualise such data.
+%
+% * The third shows the 2D view with interpolated shading, which
+%   demonstrates the improvements over the default interpolated shading.
+
+nx = 2; ny = 2;
 
 figure(100);
-nx = 3; ny = 2;
 for ii = 1:nx*ny
 
   subplot(ny,nx,ii); cla; hold on
   p = delaunay_surf(x,y,z,'N',ii-1);
   title(['Interp N = ',num2str(ii-1)])
-  shading interp
   set(p,'EdgeColor','black','linewidth',0.1)% delete this line to remove the lines
   view(3)
 
 end
 
 figure(101);
-nx = 3; ny = 2;
 for ii = 1:nx*ny
 
   subplot(ny,nx,ii); cla; hold on
-  delaunay_surf(x,y,z,'N',ii-1);
+  p = delaunay_surf(x,y,z,'N',ii-1);
   title(['Interp N = ',num2str(ii-1)])
-  shading interp
+  set(p,'edgecolor','none')
   view(2)
 
 end
 
-%%
-
 figure(102);
-nx = 2; ny = 2;
 for ii = 1:nx*ny
 
   subplot(ny,nx,ii); cla; hold on
-  delaunay_surf(x,y,z,'N',ii-1);
+  p = delaunay_surf(x,y,z,'N',ii-1);
   title(['Interp N = ',num2str(ii-1)])
+  shading interp
   view(2)
 
 end
 
-%%
 
-figure(102); clf; hold on
+%% Examples of plotting gridded data, with and without interpolation
+%
+% This section is just to make some nice examples for comparison purposes.
 
-p1 = delaunay_surf(x,y,z,'N',1);
-p2 = delaunay_surf(x,y,z,'N',0);
-set(p1,'facecolor','none','edgecolor','red')
-set(p2,'facecolor','none','linewidth',2)
+[x,y,z] = peaks(5);
+figure(98);
+subplot(3,3,1); cla; hold on
+surf(x,y,z);
+axis tight
+view(3)
+zlabel('Original data')
+
+subplot(3,3,2); cla; hold on
+surf(x,y,z);
+view(2)
+
+subplot(3,3,3); cla; hold on
+p = surf(x,y,z);
 view(2)
+set(p,'edgecolor','none')
 
+subplot(3,3,4); cla; hold on
+p = surf(x,y,z);
+axis tight
+shading interp
+view(3)
+set(p,'EdgeColor','black','linewidth',0.1)% delete this line to remove the lines
+zlabel('Interpolated shading')
+
+subplot(3,3,5); cla; hold on
+p = surf(x,y,z);
+shading interp
+view(2)
+set(p,'EdgeColor','black','linewidth',0.1)% delete this line to remove the lines
+
+subplot(3,3,6); cla; hold on
+p = surf(x,y,z);
+shading interp
+view(2)
+
+F = griddedInterpolant(x',y',z');
+[x2,y2] = ndgrid(linspace(-3,3,20));
+
+subplot(3,3,7); cla; hold on
+surf(x2,y2,F(x2,y2))
+view(3); axis tight
+zlabel('Interpolated data')
+
+subplot(3,3,8); cla; hold on
+surf(x2,y2,F(x2,y2))
+view(2);
+
+subplot(3,3,9); cla; hold on
+p = surf(x2,y2,F(x2,y2));
+view(2);
+set(p,'edgecolor','none')