autocad-dxf/Length.js

A module which can be used to parse AutoCAD dxf files and to make programmatic and geometric operations on the AutoCAD drawing entities.

const BSpline = require("./BSpline");
const ErrorMessages = require("./ErrorMessages.json");

module.exports = (entity, plane, getAxes, tolerance) => {
	if (typeof entity != "object") {
		throw new Error(ErrorMessages.INCORRECT_PARAMS);
		return;
	}
	let [ax1, ax2] = getAxes(plane);
	if (plane && ax1 === undefined && ax2 === undefined) {
		throw new Error(ErrorMessages.INCORRECT_PARAMS);
		return;
	}
	const etype = entity.subclass;
	if (etype == "AcDbLine") {
		const x1 = entity[`start_${ax1}`];
		const y1 = entity[`start_${ax2}`];
		const x2 = entity[`end_${ax1}`];
		const y2 = entity[`end_${ax2}`];
		return Math.sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
	} else if (etype == "AcDbPolyline") {
		const vertices = JSON.parse(JSON.stringify(entity.vertices));
		if (entity.type == "Closed") vertices.push(vertices[0]);
		let length = 0;
		for (let i = 1; i < vertices.length; i++) {
			const x1 = vertices[i - 1][`${ax1}`];
			const y1 = vertices[i - 1][`${ax2}`];
			const x2 = vertices[i][`${ax1}`];
			const y2 = vertices[i][`${ax2}`];
			length = length + Math.sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
		}			
		return length;
	} else if (etype == "AcDbCircle") {
		const start_angle = entity.start_angle;
		const end_angle = entity.end_angle;
		if (start_angle !== undefined && end_angle !== undefined) {
			let d;
			if (start_angle < end_angle) {
				d = Math.abs(start_angle - end_angle);
			} else {
				d = 360 - Math.abs(start_angle - end_angle);
			}				
			return 2*Math.PI*(entity.radius)*d/360;
		} else {
			return 2*Math.PI*entity.radius;
		}
	} else if (etype == "AcDbEllipse") {
		const t0 = entity.start_parameter;
		const t1 = entity.end_parameter;

		const dx = entity[`major_end_d${ax1}`];
		const dy = entity[`major_end_d${ax2}`];

		const ratio = entity.minorToMajor;

		const a = Math.sqrt(dx*dx + dy*dy);
		const b = ratio * a;

		const x = [
			-0.989400934991650,
			-0.944575023073233,
			-0.865631202387832,
			-0.755404408355003,
			-0.617876244402644,
			-0.458016777657227,
			-0.281603550779259,
			-0.095012509837637,

			 0.095012509837637,
			 0.281603550779259,
			 0.458016777657227,
			 0.617876244402644,
			 0.755404408355003,
			 0.865631202387832,
			 0.944575023073233,
			 0.989400934991650
		];

		const w = [
			0.027152459411754,
			0.062253523938648,
			0.095158511682493,
			0.124628971255534,
			0.149595988816577,
			0.169156519395003,
			0.182603415044924,
			0.189450610455068,

			0.189450610455068,
			0.182603415044924,
			0.169156519395003,
			0.149595988816577,
			0.124628971255534,
			0.095158511682493,
			0.062253523938648,
			0.027152459411754
		];

		const half = 0.5 * (t1 - t0);
		const center = 0.5 * (t1 + t0);

		let sum = 0;

		for (let i = 0; i < x.length; i++) {

			const t = half * x[i] + center;

			const s = Math.sin(t);
			const c = Math.cos(t);

			sum += w[i] * Math.sqrt(
				a*a*s*s + b*b*c*c
			);
		}

		return half * sum;							
		
		//return Math.PI*(a + b)*(1 + 3*h/(10 + Math.sqrt(4 - 3*h)));  // previous Ramanujan's second formula 
	} else if (etype == "AcDbSpline") {	
		const result = BSpline(entity);
		return result.length;  //Approximate
	}
	return;		
};