CODEWITHSUNDEEP
unity-game-enginepositionmappinglatitude-longitude
Willems
Willems

Reputation: 77

Longitude and Latitude to location on sphere in Unity

Hi all,

I'm trying to transform locations based upon longitude and latitude to a vector3 location, which will be placed on a sphere in Unity. However, the location seems to be constantly off (compared to the actual location).

I use the following code at the moment: 

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class testPosLatLong : MonoBehaviour {

    public float longi;
    public float lati;
    public float radius;
    public Transform marker;

    // Use this for initialization
    void Start () {

        // Transfer to Radians from Degrees
        float templongi = longi * Mathf.PI / 180;
        float templati = lati * Mathf.PI / 180;

        float Xpos = radius * Mathf.Cos(templati) * Mathf.Cos(templongi);
        float Ypos = radius * Mathf.Cos(templati) * Mathf.Sin(templongi);
        float Zpos = radius * Mathf.Sin(templati);

        Debug.Log ("X, Y, Z" + Xpos + " " + Ypos + " " + Zpos);

        // Set the X,Y,Z pos from the long and lat
        Instantiate(marker);
        marker.position = new Vector3 (Xpos, Zpos, Ypos);

    }

    // Update is called once per frame
    void Update () {

    }
}

I've tried to set the longitude and latitude to zero, which looks like it got the right position on the sphere:

Longitude and Latitude both 0

But when I try the longitude and latitude of Amsterdam for example it gives the following results (left side), while it should be the result on the right side.

Longitude and Latitude on 52.37022 & 4.895168

Am I missing something or what is going wrong here? I tried googling a lot, but couldn't find anything that might explain my current problem. The project itself can be found here: https://wetransfer.com/downloads/31303bd353fd9fde874e92338e68573120171205170107/1208ac%3E

Hope somebody can help.

Upvotes: 2

Views: 3097

Answers (1)

Adam B
Adam B

Reputation: 3842

I think your globe is what's wrong. It's tough to see from your images, but to me the equator looks like it's in slightly the wrong spot, and the North Pole looks to be too crowded with Greenland. I suspect is has to do with the projection you're using to paste the globe image onto the sphere.

Typically there are very complex ways of projecting 2D maps/images onto 3D surfaces. There's a whole field of geospatial analysis on how to do this accurately. It's a tough problem.

Also, The actual earth isn't exactly a sphere, so this could give you errors as well, but I would guess these would result in much smaller errors that what you describe. Accurate maps reperesent the 3D earth as a "geoid". to get locally accurate maps, people typically project data differently in small areas to maximize accuracy at a local scale. Otherwise you see large distortions. So as you zoom into a global map, the projections actually change significantly.

One possible way to test where the issue is coming from could be to set up control points of known coordinates both on your map image and on the globe, and then test to see if they line up. Like put a spike sticking out of the world at where Amsterdam SHOULD be on the globe, and where it is on the actual image. If these two don't line up then you can be pretty sure where your problem lies. This is called "Georeferencing".

I think for 3D projections you'd likely need at least 4 such "control points". You might take a look at the geospatial community on stackexchange for more detailed info on projecting maps and swapping between coordinate systems.

Upvotes: 4

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