[geos-devel] Questions about linear referencing

[David Turner]

On Mon, 2010-02-01 at 11:04 +0100, Sean Gillies wrote:
> The GEOSProject function returns a numerical value when passed a line  
> string and a point not on the line. If the point is beyond (in some  
> sense) the line's starting point, you get 0.0 (normalized). If the  
> point is past (in some sense) the line's end point, you get 1.0  
> (normalized to the line's length). If the point is otherwise off of  
> the line but not past one of its ends in that sense, you get a value  
> between 0 and 1.
> 
> Is this intended? The behavior seems like it could get rather  
> unpredictable for anything other than a perfectly straight line.

This comes from the LengthIndexedLine::project method.  That method
finds the closest point along the geometry to the input point.  That
closest point could be one of the end points.  Why is this
unpredictable?