hunterInt - 4 months ago 15

Node.js Question

I have a flight path with lat/long and elevation and I need to convert this to cartesin X,Y,Z for cesium.js.

I am running into the wall trying to convert this because I don't seem to be getting the right results from my function.

`var R = 6371;`

function polarToCartesian(latitude, longitude, elevation){

x = (R+elevation) * math.cos(latitude) * math.cos(longitude);

y = (R+elevation) * math.cos(latitude) * math.sin(longitude);

z = (R+elevation) * math.sin(latitude);

var ar = [x,y,z];

return ar;

}

I must not either have the correct formula for polar to cartesian or I don't have the correct radius of earth. I found somewhere that my radius should be 6371 but can't seem to find that same SO question for reference.

I am partialy checking if my code is correct by manually adding up the radius of the earth + altitude of the flight path at a given location and seeing if this equals the length of my x,y,z vector.

For example: x,y,z

`(3689.2472215653725,3183.2401988117012,13306.90338789763)`

is outputted when I give my function this

`-93.028,44.6942,7800`

lat,long,elevation

Could someone point me to find the right js code to accomplish this conversion?

Answer

You should be using Cesium's built-in functions for this. See `Cartesian3.fromDegrees`

and `Cartesian3.fromDegreesArray`

.

For example:

```
var result = Cesium.Cartesian3.fromDegrees(latitude, longitude, elevation);
```

Note the result will be as Cesium expects: in meters, not kilometers. This also takes into account the shape of the Ellipsoid, for which the default is WGS84 (the Earth is not a perfect sphere, as your function presumes).