[OSM-dev] Holes in contours

[Dave Stubbs]

On Tue, Sep 16, 2008 at 9:41 AM, Steve Hill <steve at nexusuk.org> wrote:
> On Tue, 16 Sep 2008, Gregory wrote:
>
>> I noticed the Cycle map has a small hole on that link, here it is zoomed
>> in:
>
> Small holes in the SRTM data are common - they are usually caused by the
> radar being obscured by a mountain, since the radar data wasn't collected
> from directly above.  The SRT missions took radar readings from the Space
> Shuttle's orbit, so it gets progressively more holey at higher latitudes as
> the angle of the radar beam becomes less perpendicular to the ground.
>
> The problem I am trying to solve is that the piste map seems to have much
> larger areas in Canada where there is no data, which do not match up with
> similar areas on the cycle map.  Since both the piste map and the cycle map
> are using the same SRTM3 data set, this shouldn't happen, and presumably is
> caused by a difference in the toolchain used.  As far as I know, both the
> piste map and cycle map are using the same toolchain, so I guess the problem
> will be down to a version specific bug in one of the tools.
>

Looking again though, your problems seem to be in the rendering rather
than the contour generation.

If you look here:
http://www.openpistemap.org/?lat=49.61316&lon=-114.41795&zoom=15&layers=B000

and then zoom one level in:
http://www.openpistemap.org/?lat=49.61316&lon=-114.41795&zoom=16&layers=B000

a whole pile of the missing contour lines reappear.
Interestingly a lot of the contours are cut at tile boundaries.

So maybe it's just your spatial index that's broken, or postgres is
only returning a partial result for some other reason (memory running
out maybe?).

Dave