QGIS Network problem - There is no route from start point to end point

Question

I am working with QGIS 3.20.0-Odense, but the same problem persists in QGIS 3.22.16 'Białowieża'.

I am working on a distance matrix, supplemented by a vector of lines (network analisys) - The output is line vector. More precise, I am trying to use the Shortest path (layer to point) algoritm, and then create the matrix.

I have researched the issue, but the solutions do not result as they should. The output is always "There is no route from start point to end point". My network has nodes, where the lines intersect.

Furthermore, I have used the algorithm connect nodes to lines, but the problem still persists.

When I use the QNEAT3, I get the distance matrix, but with incorrect attributes (distance is too small).

Both layers, points (556 features) and lines (755.000 features) are in the same CRS - EPSG:3765 - HTRS96 / Croatia TM.

Just to say, the network i downloaded from OpenStreetMap services and transformed to the same CRS as the points are).

The problem is, I could use an ORS Tools plugin, but my network is a historical one. Funny thing is, the network that is created with this plugin, get me the results. But, as I mentioned, the network must be a historical one, without new infrastructure...

Answer 1

I have been searching for the right answer in a last few weeks, since the previous solutions did not work very well.

So, since I have been working with networks that are in reality roads, this would be my answer to the question.

As a prerequisite, the network should be tidy.

First thing to do is to search for isolated network within the network. That should be done with the Disconnected Island plugin. All the islands should be connected to the the whole network. Depending on the reality, the network might have one or more network islands (e.g. in realty real islands).

It should make the picture more clearly for further analysis.

After that, the problem solving should continue with the algorithm Check validity. The test will result in 3 outputs, valid (as lines), invalid (as lines) and invalid as points (to find the invalid places). The invalid lines might be deleted if not that important.

Additional check might be done with the Geometry Checker, just to be on a safe side. It should be noted that proper tests should be applied (self intersections, self contacts, duplicate nodes, check for duplicates. Dangles are understood when dealing with roads).

The last thing to do is to install Networks and use the Connect nodes to lines algorithm to connect your points

Finaly, a topology tolerance might be set.

At last, but not least, the one thing you should probably not do is the Splits the lines tool. This tool might ruin your network, e.g. the motorway might be split by an unclassified road and create a node that in reality does not exists, which means create a path that does not exist.