System.Data.Entity.Spatial.DbGeography带有标高的距离

Question

I'm want to find the distance between 2 points on the planet (using WGS84) and System.Data.Entity.Spatial.DbGeography seemed like a good shout, but i'm not getting the expected result from the Distance function when the points have an elevation:

var geogA = DbGeography.PointFromText("POINT(179.04 89.77 100)", 4326);
var geogB = DbGeography.PointFromText("POINT(179.04 89.77 200)", 4326);
var distance = geogA.Distance(geogB); //distance is 0, not 100

I was expecting distance to be able to take the elevation into account as well - am I missing something obvious here?

I'm sure this must be fairly trivial, but I know little about the maths behind it all, so i'm probably not qualified to make that statement.

My intuition tells me, just use Pythagoras here, but i'm not 100% sure that's correct.

Answer 1

In the SQL Server Libraries Z (Elevation) is more like a Tag or a pure user defined property.

So it is not used in any calculations. This makes it similar to M which also only has meaning to my specific dataset.

If elevation actually matters to you from a Math perspective then you will have to do this add/minus after you get the geography distance results. Take care to subtract from the higher elevation.

You are adding two numbers (distance on the surface) + (elevation delta). If you use Pythagoreans theorem you have to take into account a lot of subtle logic the geography libraries are doing for you.