sub2ind error

i use this to make an accumulator array but it comes error

mat=zeros(250,250);
x=linspace(0,25.1923,100);
y=linspace(-7.9089e+003,313,100);
index=sub2ind(size(mat),round(y),round(x));

i run that code but 'out of range subscript'

that's why ? explain me please

Answer 1

[Image Analyst]

You need to convert from "real world units" into units of matrix elements. Below I used the "point-slope" formula for a line to convert your real world units into indexes. Here's one way that's fairly general for linear transforms like you used: (It's not that complicated, just try to follow the comments.)

mat=zeros(250,250);
% Create sample x and y vectors in "real world" units.
x=linspace(0,25.1923,100); % Columns
y=linspace(-7.9089e+003,313,100); % Rows.

% Figure out what indexes those are
% in terms of elements or indexes.
% These indexes will range from 1 to 100 (or the length of x or y).
slopeX = (max(x) - min(x)) / (length(x)-1)
rowIndexes = int32(1 + (x - min(x))/ slopeX)
slopeY= (max(y) - min(y)) / (length(y)-1)
columnIndexes = int32(1 + (y - min(y))/ slopeY)

% Now construct a list of all linear indices in the entire mat matrix.
% (That was wanted for some reason.)
linearIndexes = sub2ind(size(mat), rowIndexes, columnIndexes)

% Now do it for just one particular x and y 
% where x and y are in "real world" units.
x0 = 13  % Let's just say you wanted this for example.
y0 = 42
rowIndex = int32(1 + x0 / slopeX)
columnIndex = int32(1 + y0 / slopeX)
% Get the linear index of that one particular point.
linearIndex = sub2ind(size(mat),round(rowIndex),round(columnIndex))
% Report the value of mat() there:
fprintf('mat(%d) = %f\n', linearIndex, mat(linearIndex));

[Luca Santoro]

Not work for real negative coordinates

Answer 2

[Wayne King]

Your x and y vectors are not suitable for sub2ind(). You have an x vector that starts at 0 which is not a valid linear index in MATLAB and you have y-values that are negative, which are not valid linear indices in MATLAB.

Answer 3

[ike]

please help me make an accumulator array in hough if the equation y=mx+c