Re: [OpenMap Users] Issues with accuracy of polygons

From: Don Dietrick <>
Date: Tue, 15 Feb 2005 15:39:23 -0500

Hi Samarth,

On Feb 15, 2005, at 3:18 PM, Pal, Samarth wrote:

> Hi,
> We are having some issues with moving polygons around on the map. Once
> we have constructed the polygons, and we select them to move the
> vertices around, the other points that were not selected to move also
> shift a little bit on the map.
> To re-create a scenarios like this, create a polygon with ~10
> vertices. Zoom to about a scale of ~25000. If you now select the
> polygon, and then move vertex one from point A to point B, then all
> the other points have slightly moved away. Note that this is not the
> scenario of moving the whole polygon, but rather moving the individual
> vertex.
> We originally thought that this was because the resolution of a float
> since that approximately gives a resolution of about 0.5 meters ground
> distance at the equator. The movement we are noticing on the other
> points is quite greater than this - on the order of at least couple of
> hundred feet ground distance, but less than 0.1 mile. This is low
> resolution in the big picture but 200 to 300 ft movement is not that
> accurate either.
> So the question is that is this the best resolution that is supported
> by OpenMap or is it actually a bug in the drawing tool when it does
> conversions from x/y space to lat/lon space?

Yep. The polygon is reset based on the location of the drawing

It's a bug.

- Don

Don Dietrick,
BBN Technologies, Cambridge, MA

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Received on Tue Feb 15 2005 - 15:39:56 EST

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