Turning Polyline with Multiple Segments into One Single Line in QGIS?

Question

Using QGIS Valmiera (MapInfo and other software is also available)

Is there a way to convert a polyline with multiple segments into a single line? I.e. by taking the first point and the last point of the polyline and simply connecting the two.

Furthermore, is this possible to be done under a condition that say the polyline is straight enough to be considered a single line. For example if polyline is within a certain distance of the line connecting the start and the end point.

The context is I'm importing into a hydraulics software package with a pipe limit and polylines are disaggregated in this software and as a result count for thousands of pipes rather than hundreds despite being largely straight.

Answer 1

Simplify didn't do it for me. What did what I wanted (a polyline of one segment) was: Vector->Geoprocessing Tools->Dissolve.

Answer 2

You can do this with grass plugin of qgis. Import your file in grass and use v.clean.snap to connect lines (you have to set threshold of course). After that save the file as a shape and use Qgis->Dissolve. With this command you obtain a single geometry of all your lines. After that, use "multipart to singlepart" to obtain again single geometry where lines don't touch each others.

Answer 3

In QGIS I found a very comparable solution in the Vector -> Geometry Tools -> Simplify Geometries toolbox in the menu bar.

This effectively and greatly reduced the number of nodes in the polyline without compromising the overall shape of the vectors.