# How to calculate the length of a polyline across the Earth

How does one calculate the length of a polyline as a great circle distance? In this case the line only has two positions in it; i know there’s a cartesian3 `distance` function, but that’s a straight line distance.

I found this method, but it seems to be based on outdated and removed functions.

Created a methodology using the CallbackProperty showcase example.

This is assuming that a polyline already exists.

``````calculateMeasureLineLength(){
var geodesic = new Cesium.EllipsoidGeodesic();
let totalDistanceInKm = 0.0
let distLine = viewer.entities.getById("examplePoly").polyline;

if (distLine && distLine.positions) {
let startPos = distLine.positions.getValue(JulianDate.now());
let endPos = distLine.positions.getValue(JulianDate.now());

geodesic.setEndPoints(
Cartographic.fromCartesian(startPos),
Cartographic.fromCartesian(endPos)
);

var totalDistanceInMeters = Math.round(geodesic.surfaceDistance);

totalDistanceInKm = totalDistanceInMeters * 0.001;
}