pgxgrid

Find all parts of the vertical lines of a grid inside a polygon. The grid is defined by the vectors x (length nx and y (length ny). The function detects all parts of the vertical grid lines <x[i],y[0]>..<x[i],y[ny-1]> (i=0..nx-1), which are inside the polygon p.

Usage

pgxgrid(P, IP, Xvector, Yvector)

P

a closed point-list or a polygon-stream defining one or more polygons.

IP

The index of the polygon of P to be tested; 0 <= IP < pgget(P)

X

The x-scale vector of the grid.

Y

The y-scale vector of the grid.

Result

The result r is a (N+1)x3 matrix, with N is the number of vertical grid lines intersecting the polygon.

content of r[0,*]:

r[0,0]	ixmin: the X index of the first vertical line intersecting PIP
r[0,1]	ixmax: the X index of the last vertical line intersecting PIP
r[0,2]	iymin: the index of the minimum Y value of an intersection line
r[0,3]	iymax: the index of the maximum Y value of an intersection line
r[0,4]	ngrid: the accumlated number of grid points inside PIP
r[0,5]	aclen: the absolute length of the centerline
r[0,6]	rclen: the relative length of the centerline

content of r[i,*], i=1..N (one row for each intersection line):

r[i,0]	ix[i]: the X index of the intersection line
r[i,1]	iy[i]: the Y index of the first point <X[ix[i]],Y[iy[i]]> inside PIP
r[i,2]	iymin: the index of the minimum Y value of an intersection line
r[i,3]	iymax: the index of the maximum Y value of an intersection line
r[i,4]	ngrid: the accumlated number of grid points inside PIP
r[i,5]	aclen: the absolute length of the centerline
r[i,6]	rclen: the relative length of the centerline

See also

pginit, pgget, pgitest, pgiline, pgsplit, pgtrans, pghull

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