What do the response values from ArcGIS Rest API Elevation Profile function represent?

Question

So I am trying to use the ArcGIS API and asked it to profile a route between two lat/longs:

(52.106505, 1.186008)
(52.113621, 1.246862)

My results are a series of points between the two and they should include an m-value and a z-value like this:

[52.106504999653112,1.1860080002471705,-5123,0],[52.10665022396023,1.1872499188943948,-5123,138.2728000000061]

Z-value for both is -5123 and the m 0 for the first point (as expected) but then 138.27. Now these two results are around 84 meters apart and my results tell me that distance is 84. So what is M? it seems to go up by about 138 each time so what is this a measure of?

Likewise and the real question I have is what on earth is Z? Because these points are not 5km below sea level? What is the Z values units and what is 0 relative to elevation? The documentation for this function doesn't seem to give any indication?

Answer 1

The ArcGIS REST API takes points in (lon,lat) format, not (lat,lon).

The elevation at (lon=52.106505, lat=1.186008) is indeed 5km below sea level, and the separation between your points in that format is ~140m. Flip the order of your input coordinates, you should get out the results you're expecting.

There's unfortunately no standard on lat/lon order in GIS software. ArcGIS APIs tend to use (lon,lat). The clue in the documentation is that the response is returned as [x, y, z, m] which is [lon, lat, elevation, separation].