Programmer Guide/Command Reference/EVAL/pgiline: Difference between revisions

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=====pgiline - detect line intersection=====
Find all intersections of a line, defined by two points, with a polygon.
;Usage:
:<code>pgiline(<var>X</var>, <var>IX</var>, <var>PX1<sub>scalar</sub></var>, <var>PY1<sub>scalar</sub></var>), <var>PX2<sub>scalar</sub></var>, <var>PY2<sub>scalar</sub></var>)</code>
:;<var>X</var>:a [[../#polygons|closed point-list]] or a [[../#polygons|polygon-stream]] defining one or more polygons.
:;<var>IX</var>:The index of the polygon of ''X'' to be tested; 0 &le; <var>IX</var> < <code>[[../pgget|pgget]](''X'')</code>
:;<var>PX1, PY1, PX2, PY2</var>: The points <''PX1'',''PY1''> and <''PX2'',''PY2''> defining the line to be tested.
;Result: The result ''r'' is a Nx3 matrix. Each row of the matrix contains the coordinates of a point of the line and its state.
::{|class="einrahmen"
! i !! ''r''[i,0], ''r''[i,1] !! ''r''[i,2]
|-
|0
|start point of the line
|0 if the start point is outside ''X<sub>IX</sub>''<BR>1 if the start point is inside ''X<sub>IX</sub>''
|-
|1 .. N-2
|intersection point
|0 if the line leaves ''X<sub>IX</sub>''<BR>1 if the line enters ''X<sub>IX</sub>''
|-
|N-1
|end point of the line
|0 if the end point is outside ''X<sub>IX</sub>''<BR>1 if the end point is inside ''X<sub>IX</sub>''
|}
;See also: [[../pginit|pginit]], [[../pgget|pgget]], [[../pgitest|pgitest]], [[../pgxgrid|pgxgrid]], [[../pgsplit|pgsplit]], [[../pgtrans|pgtrans]], [[../pghull|pghull]]


=====Usage:=====
[[../#Functions|<function list>]]
 
<code><var>IS</var> := pgILine( {pg_stream}<var>XS</var>, {number}<var>IX</var>, {number}<var>X1</var>, {number}<var>Y1</var>, {number}<var>X2</var>, number{<var>Y2</var>} )</code>
 
=====Description:=====
 
Detect intersections of a simple-polygon with a straight line.
 
=====Parameters:=====
 
;<var>XS</var>
 
:The polygon stream containing the simple polygon, or point list describing the simple polygon.
 
;<var>IX</var>
 
:The index of the polygon describing the simple polygon.
 
;<var>X1, Y1</var>
 
:The x/y coordinate of the first point in the line.
 
;<var>X2, Y2</var>
 
:The x/y coordinate of the last point in the line.
 
=====Result:=====
 
Detect intersections of the line <<var>X1</var>,<var>Y1</var>>..<<var>X2</var>,<var>Y2</var>> and the polygon <var>XS</var>[<var>IX</var>].
 
The result <var>IS</var> is an "N x 3" matrix:
 
row 0: col0,col1 x and y of start-point
 
col2 0 if start-point outside and 1 if start-point inside the polygon
 
...
 
row i: col0,col1 x and y of intersection point i (i = 1 .. N-2)
 
col2 0 if the line leaves and 1 if the line enters the polygon
 
...
 
row N-1: col0,col1 x and y of end-point
 
col2 0 if end-point outside and 1 if end-point inside the polygon

Latest revision as of 20:11, 21 April 2011

Find all intersections of a line, defined by two points, with a polygon.

Usage
pgiline(X, IX, PX1scalar, PY1scalar), PX2scalar, PY2scalar)
X
a closed point-list or a polygon-stream defining one or more polygons.
IX
The index of the polygon of X to be tested; 0 ≤ IX < pgget(X)
PX1, PY1, PX2, PY2
The points <PX1,PY1> and <PX2,PY2> defining the line to be tested.
Result
The result r is a Nx3 matrix. Each row of the matrix contains the coordinates of a point of the line and its state.
i r[i,0], r[i,1] r[i,2]
0 start point of the line 0 if the start point is outside XIX
1 if the start point is inside XIX
1 .. N-2 intersection point 0 if the line leaves XIX
1 if the line enters XIX
N-1 end point of the line 0 if the end point is outside XIX
1 if the end point is inside XIX
See also
pginit, pgget, pgitest, pgxgrid, pgsplit, pgtrans, pghull

<function list>

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