[OSM-newbies] Experiments in mapping new buildings

[James Ewen]

On Sun, Jan 27, 2013 at 2:36 PM, Tom Taylor <tom.taylor.stds at gmail.com> wrote:

> I've gotten more satisfactory results by sighting along each edge and
> collecting a single averaged waypoint on each side of the building to let me
> draw a line. This takes a while -- eight points just for a rectangular
> building. Cold work at -15 C. (5 degrees F.), I must say. At the end of it,
> I know the estimated error at each point, and the results seem satisfactory
> when I draw them out.

Extending the sight lines off the edges of buildings also works to
reduce your angular errors.

If you are standing 100 meters away from a building edge, and sighting
along it to get lined up properly, then collecting an averaged
waypoint with an estimated error of 3 meters would give a possible
angular error of about 1.72 degrees.

If the side of the building you are sighting along is 10 meters in
length, then the error at the close end of the building would be on
the magnitude of 0.3 meters.

This is only significant for getting the angles correct. The GPS
locations can still all be shifted horizontally from where they should
be by the common error.

-- 
James
VE6SRV