[OSM-dev] Problem with Postgresql / Mapnik / SRTM Contours

[Andy Allan]

On Sun, Nov 23, 2008 at 6:35 PM, Keith Sharp <kms at passback.co.uk> wrote:

> Anyone have any thoughts as to what is causing this?

Yep, it's a boundary effect at the edge of each SRTM tile. What you
are seeing is the end of the contour straightening out after it gets
to the last datapoint in the SRTM data. There's a corresponding start
of the same level contour in the next file over, and because the edge
points are shared and overlapping by the SRTM tiles everything meets
fine. So you get a kind of:
\
 \_

and

_
 \
  \

meeting at the same point. It's not impossible to detect and edit the
polyline, or even see if there's a gdal_contour option to fix it, but
I haven't spent any time doing so.

Cheers,
Andy