"Nelson A. de Oliveira" <nao...@gmail.com> writes: > I really don't know if the proper term is "altimetric quota" in > English, sorry. > > What we have are some places where the elevation at some points were > measured. It's similar to man_made=survey_point but without any > physical objects or marks there; somebody just measured the elevation > at that point and charted it.
In English and US surveying practice, we have two things: "benchmark": This is a physical monument (brass disk usually, for < 100 year old marks). It has an established orthometric height from leveling. The horizontal coordinates are not necessarily known precisely, just as the elevation of horizontal controls is not necessarily known precisely. These are the vertical control network making up our NGVD29 and NAVD88 datums. Definitely a survey_point. "spot elevation": This is a notation on a topographic map giving the elevation at some point. There is not necessarily a mark on the ground. These probably do not belong in OSM, but if they are recorded in survey databases, it seems reasonable. Now, control points are likely to be 3D, and use GPS, and have ellipsoidal coordinates and an elevation derived from ellipsoidal height and a geoid model. For measured spot elevations that have some sense of officialness, I would be tempted to call them man_made=survey_point, perhaps with survey_poinrt=none :-)
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