MATLAB: Problem with data triangulation

3d scattersurftriangulationtrisurf

Dear Matlab users,

I am trying to visualize a surface made of 3d scattered points. It is not an F(x,y) -> z function, z is just a scalar associated to (x,y) pairs. The x and y pairs form a fairly uniform rectangular grid on the xy plane. However, as soon as I try to use trisurf, the data are triangulated in an unexpected fashion.

I am actually interested in "connecting" these 3d points, not in an interpolation. The surface which can be glimpsed from scatter3 appears to be quite regular, but I wasn't succesfull in using trisurf or even surf.

Can you help me in achieving this goal? I am probably missing something in how the delaunay triangulation works.

Thank you in advance,

Leonardo

Best Answer

It's because of different scales

try to scale your data

dx = max(x)-min(x);
y1 = (y-min(y))/(max(y)-min(y))*dx;
T = delaunay(x,y1);
trisurf(T, x, y, z)
axis vis3d

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I suggest http://www.mathworks.com/help/matlab/ref/spline.html

x = 1 : length(psdn);
x128 = linspace(x(1), x(end), 128);
p128 = spline(x, psdn, x128);
plot(x128, p128);

MATLAB: I have an array of data from a sensor which varies from positive to negative continuously. I want to find the peak value of each set of positive numbers and negative numbers.

>> findpeaks(X(X>0))
ans =
  Columns 1 through 10
    4.5190    4.5260    3.3360    3.1910    2.4630    1.8080    1.7910    1.3260    1.0030    0.7530
  Columns 11 through 20
    0.5650    0.4140    0.3060    0.3030    0.2290    0.2280    0.1710    0.1710    0.1300    0.1180
  Columns 21 through 30
    0.0980    0.0740    0.0520    0.0540    0.0410    0.0410    0.0320    0.0250    0.0190    0.0200
  Columns 31 through 40
    0.0020    0.0150    0.0150    0.0150    0.0110    0.0110    0.0110    0.0110    0.0070    0.0080
  Columns 41 through 50
    0.0090    0.0090    0.0090    0.0020    0.0040    0.0070    0.0020    0.0030    0.0030    0.0040
  Columns 51 through 59
    0.0050    0.0020    0.0020    0.0030    0.0030    0.0030    0.0030    0.0020    0.0020
>> abs(findpeaks(-X(X<0)))
ans =
  Columns 1 through 10
    3.8980    3.7790    2.8760    2.1120    2.1030    1.5570    1.5540    1.1540    0.8550    0.6340
  Columns 11 through 20
    0.4610    0.4700    0.3490    0.2600    0.1950    0.1450    0.1090    0.0790    0.0810    0.0590
  Columns 21 through 30
    0.0600    0.0600    0.0450    0.0450    0.0340    0.0270    0.0270    0.0200    0.0150    0.0150
  Columns 31 through 40
    0.0150    0.0100    0.0030    0.0100    0.0100    0.0100    0.0020    0.0060    0.0060    0.0060
  Columns 41 through 50
    0.0060    0.0050    0.0040    0.0020    0.0040    0.0040    0.0040    0.0040    0.0020    0.0020
  Columns 51 through 60
    0.0020    0.0020    0.0030    0.0030    0.0020    0.0020    0.0020    0.0020    0.0020    0.0020
  Columns 61 through 64
    0.0020    0.0020    0.0020    0.0020
>>

findpeaks is in Signal Processing Toolbox...

Best Answer

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