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geometry.3tcl

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NAME

math::geometry - Geometrical computations

SYNOPSIS

package require Tcl ?8.3?

package require math::geometry ?1.0.3?

::math::geometry::angle line

::math::geometry::calculateDistanceToLine P line

::math::geometry::calculateDistanceToLineSegment P linesegment

::math::geometry::calculateDistanceToPolyline P polyline

::math::geometry::findClosestPointOnLine P line

::math::geometry::findClosestPointOnLineSegment P linesegment

::math::geometry::findClosestPointOnPolyline P polyline

::math::geometry::lengthOfPolyline polyline

::math::geometry::movePointInDirection P direction dist

::math::geometry::lineSegmentsIntersect linesegment1 linesegment2

::math::geometry::findLineSegmentIntersection linesegment1 linesegment2

::math::geometry::findLineIntersection line1 line2

::math::geometry::polylinesIntersect polyline1 polyline2

::math::geometry::polylinesBoundingIntersect polyline1 polyline2 granularity

::math::geometry::intervalsOverlap y1 y2 y3 y4 strict

::math::geometry::rectanglesOverlap P1 P2 Q1 Q2 strict

::math::geometry::bbox polyline

::math::geometry::pointInsidePolygon P polyline

::math::geometry::rectangleInsidePolygon P1 P2 polyline

::math::geometry::areaPolygon polygon

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DESCRIPTION

The math::geometry package is a collection of functions for computations and manipulations on two-dimensional geometrical objects, such as points, lines and polygons.

The geometrical objects are implemented as plain lists of coordinates. For instance a line is defined by a list of four numbers, the x- and y-coordinate of a first point and the x- and y-coordinates of a second point on the line.

The various types of object are recognised by the number of coordinate pairs and the context in which they are used: a list of four elements can be regarded as an infinite line, a finite line segment but also as a polyline of one segment and a point set of two points.

Currently the following types of objects are distinguished:

•

point - a list of two coordinates representing the x- and y-coordinates respectively.

•

line - a list of four coordinates, interpreted as the x- and y-coordinates of two distinct points on the line.

•

line segment - a list of four coordinates, interpreted as the x- and y-coordinates of the first and the last points on the line segment.

•

polyline - a list of an even number of coordinates, interpreted as the x- and y-coordinates of an ordered set of points.

•

polygon - like a polyline, but the implicit assumption is that the polyline is closed (if the first and last points do not coincide, the missing segment is automatically added).

•

point set - again a list of an even number of coordinates, but the points are regarded without any ordering.

PROCEDURES

The package defines the following public procedures:

::math::geometry::angle line

Calculate the angle from the positive x-axis to a given line (in two dimensions only).

line list Coordinates of the line

::math::geometry::calculateDistanceToLine P line

Calculate the distance of point P to the (infinite) line and return the result

P list List of two numbers, the coordinates of the point

line list List of four numbers, the coordinates of two points

on the line

::math::geometry::calculateDistanceToLineSegment P linesegment

Calculate the distance of point P to the (finite) line segment and return the result.

P list List of two numbers, the coordinates of the point

linesegment list List of four numbers, the coordinates of the

first and last points of the line segment

::math::geometry::calculateDistanceToPolyline P polyline

Calculate the distance of point P to the polyline and return the result.

P list List of two numbers, the coordinates of the point

polyline list List of numbers, the coordinates of the

vertices of the polyline

::math::geometry::findClosestPointOnLine P line

Return the point on a line which is closest to a given point.

P list List of two numbers, the coordinates of the point

line list List of four numbers, the coordinates of two points

on the line

::math::geometry::findClosestPointOnLineSegment P linesegment

Return the point on a line segment which is closest to a given point.

P list List of two numbers, the coordinates of the point

linesegment list List of four numbers, the first and last

points on the line segment

::math::geometry::findClosestPointOnPolyline P polyline

Return the point on a polyline which is closest to a given point.

P list List of two numbers, the coordinates of the point

polyline list List of numbers, the vertices of the polyline

::math::geometry::lengthOfPolyline polyline

Return the length of the polyline (note: it not regarded as a polygon)

polyline list List of numbers, the vertices of the polyline

::math::geometry::movePointInDirection P direction dist

Move a point over a given distance in a given direction and return the new coordinates (in two dimensions only).

P list Coordinates of the point to be moved

direction double Direction (in degrees; 0 is to the right, 90

upwards)

dist list Distance over which to move the point

::math::geometry::lineSegmentsIntersect linesegment1 linesegment2

Check if two line segments intersect or coincide. Returns 1 if that is the case, 0 otherwise (in two dimensions only).

linesegment1 list First line segment

linesegment2 list Second line segment

::math::geometry::findLineSegmentIntersection linesegment1 linesegment2

Find the intersection point of two line segments. Return the coordinates or the keywords "coincident" or "none" if the line segments coincide or have no points in common (in two dimensions only).

linesegment1 list First line segment

linesegment2 list Second line segment

::math::geometry::findLineIntersection line1 line2

Find the intersection point of two (infinite) lines. Return the coordinates or the keywords "coincident" or "none" if the lines coincide or have no points in common (in two dimensions only).

line1 list First line

line2 list Second line

::math::geometry::polylinesIntersect polyline1 polyline2

Check if two polylines intersect or not (in two dimensions only).

polyline1 list First polyline

polyline2 list Second polyline

::math::geometry::polylinesBoundingIntersect polyline1 polyline2 granularity

Check whether two polylines intersect, but reduce the correctness of the result to the given granularity. Use this for faster, but weaker, intersection checking.

How it works:

Each polyline is split into a number of smaller polylines, consisting of granularity points each. If a pair of those smaller lines' bounding boxes intersect, then this procedure returns 1, otherwise it returns 0.

polyline1 list First polyline

polyline2 list Second polyline

granularity int Number of points in each part (<=1 means check

every edge)

::math::geometry::intervalsOverlap y1 y2 y3 y4 strict

Check if two intervals overlap.

y1,y2 double Begin and end of first interval

y3,y4 double Begin and end of second interval

strict logical Check for strict or non-strict overlap

::math::geometry::rectanglesOverlap P1 P2 Q1 Q2 strict

Check if two rectangles overlap.

P1 list upper-left corner of the first rectangle

P2 list lower-right corner of the first rectangle

Q1 list upper-left corner of the second rectangle

Q2 list lower-right corner of the second rectangle

strict list choosing strict or non-strict interpretation

::math::geometry::bbox polyline

Calculate the bounding box of a polyline. Returns a list of four coordinates: the upper-left and the lower-right corner of the box.

polyline list The polyline to be examined

::math::geometry::pointInsidePolygon P polyline

Determine if a point is completely inside a polygon. If the point touches the polygon, then the point is not completely inside the polygon.

P list Coordinates of the point

polyline list The polyline to be examined

::math::geometry::rectangleInsidePolygon P1 P2 polyline

Determine if a rectangle is completely inside a polygon. If polygon touches the rectangle, then the rectangle is not complete inside the polygon.

P1 list Upper-left corner of the rectangle

P2 list Lower-right corner of the rectangle

polygon list The polygon in question

::math::geometry::areaPolygon polygon

Calculate the area of a polygon.

polygon list The polygon in question

BUGS, IDEAS, FEEDBACK

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category math :: geometry of the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883]. Please also report any ideas for enhancements you may have for either package and/or documentation.

KEYWORDS

angle, distance, line, math, plane geometry, point

COPYRIGHT

 Copyright (c) 2004 by Ideogramic ApS and other parties