calling isosurface without specifying isovalue

Hi,

If i call isosuface without specifying the isovalue what is the lower limit of values with which the surface is created?

I can see that it is not zero because with my data if i call isosurface with isovalue = 0 i get a different result compared to isovalue = []

Thanks

matt

[Matthew O'Brien]

Does anyone have an answer for this? How is the isovalue determined when it is not defined by the user?

Thanks

Matt

Answer 1

[Grzegorz Knor]

When the isovalue is not defined Matlab determines it by calling isovalue function.

type isovalue

returns the following code:

function val = isovalue(data)
%ISOVALUE  Isovalue calculator.
%   VAL = ISOVALUE(V) calculates an isovalue from data V using hist
%   function.  Utility function used by ISOSURFACE and ISOCAPS.
%   Copyright 1984-2002 The MathWorks, Inc. 
%   $Revision: 1.6 $  $Date: 2002/06/17 13:37:43 $
% only use about 10000 samples
r = 1;
len = length(data(:));
if len > 20000
r = floor(len/10000);
end
[n x] = hist(data(1:r:end),100);
% remove large first max value
pos = find(n==max(n));
pos = pos(1);
q = max(n(1:2));
if pos<=2 & q/(sum(n)/length(n)) > 10
n = n(3:end); 
x = x(3:end);
end
% get value of middle bar of non-small values
pos = find(n<max(n)/50);
if length(pos) < 90
x(pos) = [];
end
val = x(floor(length(x)/2));