Graphics |
The contourc
function calculates the contour matrix for the other contour functions. It is a low-level function that is not called from the command line.
The contouring algorithm first determines which contour levels to draw. If you specified the input vector v
, the elements of v
are the contour level values, and length(v)
determines the number of contour levels generated. If you do not specify v
, the algorithm chooses no more than 20 contour levels that are divisible by 2 or 5.
The contouring algorithm treats the input matrix Z
as a regularly spaced grid, with each element connected to its nearest neighbors. The algorithm scans this matrix comparing the values of each block of four neighboring elements (i.e., a cell) in the matrix to the contour level values. If a contour level falls within a cell, the algorithm performs a linear interpolation to locate the point at which the contour crosses the edges of the cell. The algorithm connects these points to produce a segment of a contour line.
contour
, contour3
, and contourf
return a two-row matrix specifying all the contour lines. The format of the matrix is
The first row of the column that begins each definition of a contour line contains the value of the contour, as specified by v
and used by clabel
. Beneath that value is the number of (x,y) vertices in the contour line. Remaining columns contain the data for the (x,y) pairs. For example, the contour matrix calculated by C = contour(peaks(3))
is
The circled values begin each definition of a contour line.
Drawing a Single Contour Line at a Desired Level | Changing the Offset of a Contour |
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