[OSM-dev] Altitude data & (cycle) route profiles

Sjors Provoost sjors at sprovoost.nl
Sun Mar 30 12:05:53 BST 2008


On Sat, Mar 29, 2008 at 3:14 PM, MilesTogoe <miles.togoe at gmail.com> wrote:
> Frederik Ramm wrote:
>  > Hi,
>  >> I was thinking about adding nodes to long ways. This may sound a bit
>  >> ugly at first, but not if you consider the fact that the SRTM actually
>  >> provides real information about these points along long ways. It is
>  >> just that the latitude and longitude are not reliable, only the
>  >> altitude is.
>  >>
>  >
>  > Doesn't sound very good to me, adding nodes to existing ways just to
>  > import height... I'd rather have the height as a separate info. Much
>  > like a road that enters a forest; I don't put a node at that point
>  > just to say that this node represents the road entering the forest - I
>  > just model the forest as an extra entity and whoever needs to can
>  > compute the point.
>  >
>  > Also, having SRTM data as nodes in OSM touches on the often discussed
>  > topic of immutable data. Would it be ok for people to edit individual
>  > SRTM nodes?
>  >
>  > I'd also recommend to first do an analysis about the impact on OSM
>  > altogether, i.e. by how much would the planet file grow by importing
>  > SRTM data like you suggest? If renderers would start to use that
>  > information, then we'd suddenly have not a single "empty" tile
>  > anymore, every land tile on the planet would have information on it
>  > (right?), how would taht impact storage requirements for tile servers
>  > etc.? - Not saying that any of these could be a show-stopper, it's
>  > just that such an analysis should be part of the plan.
>  >
>  Actually the vertical inflection points (bottom, change, or top of
>  vertical curve) along a way are very useful points to have even if they
>  are along a tangent section.   The inflection points are used for sight
>  distance, drainage issues, calculation of grade or steepness,
>  calculation of traveled distance, etc.  Each node and inflection point
>  should have the lat, long, and elevation.  A straight line but up and
>  down way will have a greater travel distance than a flat way.  As a
>  civil engineer, I've always thought 2-D points are lacking and should
>  always be 3-D points.   Is it more storage, processing/retrieval cost ?
>  Sure, but it's important data.

I agree with Frederik that the SRTM nodes might not be a good idea,
because they should then be immutable.

I tend to agree with Miles here on the need to have 3-D in stead of
2-D nodes. My current understanding of nodes is that they represent
*where* something is, not *what* it is. In that case I would argue
that the altitude is part of 'where' and whether it is a forest is
part of *what*. In that case altitude should be part of the node and
forest should be a tag. I am also thinking about cities here; you can
have two subways, a road and a bridge at one lat & lon position. If
altitude is not a seperate layer of information, but part of the nodes
that make up these subways and roads, there is no problem here.

I also agree with Frederik about analyzing the potential impact of
different approaches. So I will include such an analysis in the
proposal and somewhere during the project we will have this discussion
again with some numbers and examples so support it.

Kind regards,

Sjors




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