[OSM-talk] Contour lines

[Steve Hill]

On Tue, 13 Apr 2010, Andrew Errington wrote:

> My GPS accuracy (reported
> by the device itself) is at best 4m, but in mountainous regions or in cities
> it is 5m or 6m at best, often worse.  How accurate is my mouse when I click
> on a pixel?  Visually I am interpolating the (inaccurate) GPS trace to get a
> smooth, pleasing curve or shape.  Although we strive for accuracy you have to
> remember we are not surveying, we are making a map; there is a difference.

Well yes, but the SRTM DEM has 90 metre pixels.  If you're using the data 
that has been processed into contour lines then that is going to be a 
whole lot worse even before you start taking into account stuff like void 
filling and contour smoothing.  Like it or not, tracing SRTM contours is 
probably going to leave you a couple of orders of magnitude away from GPS 
accuracy.

-- 

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence