Programmer Guide/Command Reference/EVAL/pgxgrid: Difference between revisions
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{{DISPLAYTITLE:{{SUBPAGENAME}}}} | {{DISPLAYTITLE:{{SUBPAGENAME}}}} | ||
= | 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 <code><''x''[i],''y''[0]>..<''x''[i],''y''[''ny''-1]> (i=0..''nx''-1)</code>, which are inside the polygon ''p''. | ||
;Usage: | |||
:<code>pgxgrid(<var>P</var>, <var>IP</var>, <var>X<sub>vector</sub></var>, <var>Y<sub>vector</sub></var>)</code> | |||
:;<var>P</var>:a [[../#polygons|closed point-list]] or a [[../#polygons|polygon-stream]] defining one or more polygons. | |||
:;<var>IP</var>:The index of the polygon of ''P'' to be tested; 0 ≤ <var>IP</var> < <code>[[../pgget|pgget]](''P'')</code> | |||
:;<var>X</var>: The x-scale vector of the grid. | |||
:;<var>Y</var>: 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,*]: | |||
::{|class="einrahmen" | |||
|''r''[0,0] ||''ixmin'' | |||
|the ''X'' index of the first vertical line intersecting ''P<sub>IP</sub>'' | |||
|- | |||
|''r''[0,1] ||''ixmax'' | |||
|the ''X'' index of the last vertical line intersecting ''P<sub>IP</sub>'' | |||
|- | |||
|''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 ''P<sub>IP</sub>'' | |||
|- | |||
|''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): | |||
::{|class="einrahmen" | |||
|''r''[i,0] ||''ix'' | |||
|the ''X'' index of the intersection line i | |||
|- | |||
|''r''[i,1] ||''iy'' | |||
|the ''Y'' index of the first point <''X''[''ix''],''Y''[''iy'']> i inside ''P<sub>IP</sub>'' | |||
|- | |||
|''r''[i,2] ||''ny'' | |||
|the number of ''Y'' points inside ''P<sub>IP</sub>'' | |||
|- | |||
|''r''[i,3] ||''ymin'' | |||
|the y value of the point where the intersection line i enters the polygon ''P<sub>IP</sub>'' | |||
|- | |||
|''r''[i,4] ||''ymax'' | |||
|the y value of the point where the intersection line i leaves the polygon ''P<sub>IP</sub>'' | |||
|- | |||
|''r''[i,5] ||''acofs'' | |||
|the absolute length of the centerline from the begin to intersection line i | |||
|- | |||
|''r''[i,6] ||''rclen'' | |||
|the relative length of the centerline from the begin to intersection line i | |||
|} | |||
:Notes: | |||
:*The centerline is the line defined by the centerpoints <''X''[i],(''ymin''<sub>i</sub>+''ymax''<sub>i</sub>)/2> of all intersection lines. For the computation of ''aclen'' and ''acofs''<sub>i</sub> the x- and y-values of the points are used, while ''rclen'' and ''rcofs''<sub>i</sub> are computed from the x- and y-indices. | |||
:*The function fails if a vertical grid line intersects the polygon more than 2 times. | |||
;See also: [[../pginit|pginit]], [[../pgget|pgget]], [[../pgitest|pgitest]], [[../pgiline|pgiline]], [[../pgsplit|pgsplit]], [[../pgtrans|pgtrans]], [[../pghull|pghull]] | |||
[[../#Functions|<function list>]] | |||
Latest revision as of 20:09, 21 April 2011
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 the X index of the intersection line i r[i,1] iy the Y index of the first point <X[ix],Y[iy]> i inside PIP r[i,2] ny the number of Y points inside PIP r[i,3] ymin the y value of the point where the intersection line i enters the polygon PIP r[i,4] ymax the y value of the point where the intersection line i leaves the polygon PIP r[i,5] acofs the absolute length of the centerline from the begin to intersection line i r[i,6] rclen the relative length of the centerline from the begin to intersection line i
- Notes:
- The centerline is the line defined by the centerpoints <X[i],(ymini+ymaxi)/2> of all intersection lines. For the computation of aclen and acofsi the x- and y-values of the points are used, while rclen and rcofsi are computed from the x- and y-indices.
- The function fails if a vertical grid line intersects the polygon more than 2 times.
