Projecting the world flat - distance tool

[Lwe]

Hi,

I was just checking the distance between two points and thought i could use Pythagoras with x, y coordinates when using projections for example EPSG:25832

But the distance calculated by distance tool is different.

If you put in these coordinates

id;x,y

1;724640;6178680

2;724940;6179080

They should be 500m apart using Pythagoras, but distance tool calculate them to be 498,5m

Even for just 1m difference the distance tool says 0,996m

id;x,y

1;724640;6178680

2;724641;6178680

Is it a setting I'm missing or something else causing this difference?

There is a workflow attached

Thanks

Lars

[KaneG · Accepted solution]

Hi Lars,

Check out the explanation on calcs by @RobertB in this post. It explains how Alteryx calculates those distances and so may give you an idea as to why you are getting something different.

Kane

[Lwe]

Hi Kane,

Thanks.

To me it seems like a lot that we should "lose" 4mm per meter just because the earth is round...

If thats the right interpretation of  Alteryx calculates distances "ellipsoidally", i.e. on the surface of the WGS84 ellipsoid

Potentially it could be some interesting discussions with clients why 1m is not 1m and why we could'nt just move the projections 4mm.

But since we mostly calculate distance to shop, forest, coast line etc which is not a fixed known distance, I guess we can avoid these discussion if we don't bring them up ourselves...

We can close this post:)

Lars