[postgis-users] Linear Referencing: Create Measure

[strk at refractions.net]

On Tue, Aug 01, 2006 at 12:01:26AM -0400, Christoph Spoerri wrote:
> Strk,
> 
> how are multiline string handled in the LRS functions? Can they be used in 
> those functions? If yes, is  linesegement 'drawn'/created between the end 
> points of two line strings?

line_interpolate_point(), line_substring() and line_locate_point()
only work against LINESTRINGS.
locate_along_measure() and locate_between_measures() work with
MULTILINESTRINGS also, but w/out need to interpret their semantic
except for M being consistently set (see manual).

> Depending on those answere, the measure functionality should be designed 
> accordingly. One options would be to give the user the choice if a 
> multilinestring should be a 'linestring' with gaps or a collection of 
> linestrings which have all the same start measure and the same end measure 
> (in case % are used).

Should you also ensure that for 'lines with gaps' lines are really oriented
as they should ? What determines the gap in the first place ? Is the gap
part of the information or is it just noise ? Would it make sense to fill
the gap first and *then* apply the function ?

> Based on my work with LRS, having the 'gap ' solution makes the most sense in 
> case the linestrings have gaps.

Isn't this a tautology ? :)

--strk;