3

I am not a geoscientist (I do computer graphics), however I am trying to render some geospatial data encoded as a WKT file.

I have a POLYGON with 2 coordinates per point, which seems to be representing latitude and longitude values (this is a guess on my end).

I use spherical coordinates to map these points onto euclidean (x,y,z) points for rendering.

The first problem I am having is, I am calculating latitude as an angle from the z axis (which matches the north pole) and latitude from the x axis (which seems to intersect with Greenwich meridian).

To my understanding this should guarantee correct positioning, alas what I get is a very misplaced Canada. Moreover, even when I manage to place the border on the correct region, it is clear the border outline is highly deformed with regard to the earth sphere.

enter image description here

This is the projection formula I am using to project the border:

Eigen::Vector3d SphericalCoordinatesToEuclidean(const Eigen::Vector2d& point)
{
    const double longitude = (point.y()) * 2.f * M_PI / 360.f;
    const double latitude = (point.x()) * 2.f * M_PI / 360.f;

    return {
        sin(latitude) * sin(longitude), sin(latitude) * cos(longitude), cos(latitude)};
}

The full data set is gigantic, this is just the section comprising the canadian border (every 2 values seem to be a point):

https://gist.github.com/Makogan/1aec1ea701ae3c8cb3653506bc9d8873

4
  • 4
    Longitudes -> X | Latitudes -> Y. Latitudes origin at the Equator with an extent of +/-90° (180°).
    – geozelot
    Jun 17 at 7:16
  • what a silly mistake on my end.
    – Makogan
    Jun 17 at 18:14
  • yeah, I consider myself to be extraordinarily familiar with these two, yet I I have to give it two seconds each time I go Euclidean with them...how did it go? Might want to self answer the solution, if it worked.
    – geozelot
    Jun 17 at 19:16
  • That was the problem, I swapped the coordinates, and also my angle must be computed from the equator not the axis of rotation, so I had to add pi / 2 to the latitude
    – Makogan
    Jun 17 at 20:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.