Change default topology tolerance to 0.000001
josephholler opened this issue · 1 comments
I'm attaching a very simple example geopackage with a layer, roads
to be used as a network and another layer, parks
to be used as start points for creating Iso-Areas. qneat3test.zip
Specifically, I'm running Iso-Area as Pointcloud (From Layer) with distance optimization of just 500 meters to test. I originally digitized this data with snapping enabled and densified the line geometries such that some start points are exactly coincident with vertices in the road network-- or at least coincident within the margin of error of precision with which the coordinates are stored.
The crazy thing is that without modelling one-way travel, the park with ParkName FC
only has an iso-area going one direction on the road. However, if I change the topology tolerance to 0.000001
from 0.000000
, it works just fine. That's just a fraction of a millimeter, so I'm confused as to why this makes a difference.
I can only guess that something is going awry in adding a start point to the network if the start point is coincident with an existing vertex. The same thing happens with the QGIS algorithm Service Area (From Layer)
, so the root of the problem is probably in the QGIS code.
I can't attribute this to an error with the network data, because the startpoint in question is in the middle of a line feature. In other words, it's clearly not a failure of one line to connect to another in the network due to digitizing errors.
Either way, an extremely small tolerance of less than 1 millimeter apparently fixes the problem, so could this be the default?
I have never encountered this problem but I am glad you found a way around - we can definitely change the default value of the tolerance parameter as you proposed it.