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CalcPolygonArea(data)

Last updated January 26, 2004

author

Tim Dudek

Version: 1 | Requires: CF5 | Library: MathLib

Description:
Purpose = Calcuate the area of an N sided irregular polygon. Formula = Area = 1/2 * ((x1+x2)(y1-y2)+(x2+x3)(y2-y3)+...+(xn+x1)(yn-y1)) Units = Units out are the same units as units in. Input = Array of X,Y points making up the polygon. Array must have at least three items.

Return Values:
Returns a number.

Example:

<cfset p = arrayNew(1)>
<cfset p[1] = structNew()>
<cfset p[1].x = 0>
<cfset p[1].y = 0>
<cfset p[2] = structNew()>
<cfset p[2].x = 5>
<cfset p[2].y = 0>
<cfset p[3] = structNew()>
<cfset p[3].x = 5>
<cfset p[3].y = 5>
<cfset p[4] = structNew()>
<cfset p[4].x = 0>
<cfset p[4].y = 5>

Parameters:

Name Description Required
data Array of structs Yes

Full UDF Source:

/**
 * Calculates the area of an irregular N sided Polygon.
 * 
 * @param data 	 Array of structs (Required)
 * @return Returns a number. 
 * @author Tim Dudek (tim@igl.net) 
 * @version 1, January 26, 2004 
 */
function CalcPolygonArea(data) {
	var area = "0";
	var i = 1;

	// Check for valid Stucture with at least 3 records
	if(not isArray(data) or arrayLen(data) lte 2) return 0;
	
	data[arrayLen(data)+1] = structNew();
	data[arrayLen(data)].x = data[1].x;
	data[arrayLen(data)].y = data[1].y;
	

	// Loop through the structure performing the area calculation.
	// Formula = Area = 1/2 * ((x1+x2)(y1-y2)+(x2+x3)(y2-y3)+...+(xn+x1)(yn-y1))
	for(; i LT arrayLen(data) ; i=i+1) {
		area = area + ( data[i+1].x-data[i].x) * (data[i+1].y + data[i].y) / 2;
	}
	
	// Only return positive values.
	return abs(area);
}
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