[Tagging] Elevation and height on vertical features

[Aaron Spaulding]

Hi all,

I’ve been working on generating 3D meshes based on OSM data and I ran into a problem. Vertical features like 'natural=cliff', 'barrier=retaining_wall’ and 'waterway=waterfall' occupy two points in physical space, but because of the 2D nature of OSM its ambiguous which side of the feature that the ‘ele’ tag applies.

For example, if I have a cliff there are two scenarios:

1. The ‘ele’ tag refers to the high side of the cliff, and the ‘height’ is how far down it is to the bottom of the cliff.

2. The ‘ele’ tag refers to the low side of the cliff, and the 'height' is how far up it is to the top of the cliff.

Either of these models can be used. I think option 1 makes the most sense, but I’d like to know what the community consensus is.

Aaron