[GRASS-user] v.net.distance - from feature was not reachable

[Daniel McInerney]

Hi List,

We are using v.net.distance to calculate the shortest path between two 
points on a river network, but have been experiencing some issues in 
both grass 7.4 and 7.9. In some instances, we need to add a new vector 
line (stream) to the river network, which we have done using v.patch as 
follows:

v.patch input=river_network,stream output=river_network_with_stream

We then clean the output as follows:

v.clean input=river_network_with_stream 
output=river_network_with_stream_clean tool=rmdupl,break,snap

We then run the following steps to calculate the shortest path (based on 
the documentation [1]), where the vector dataset (start_point) is 
located on the above-mentioned stream and the end_point is located on 
the river network:

v.net input=river_network_with_stream_clean points=start_point 
output=river_net operation=connect thresh=100 arc_layer=1 node_layer=2 
--overwrite

v.net input=river_net points=end_point output=river_net2 
operation=connect thresh=100 arc_layer=1 node_layer=3 --overwrite

The resulting output of v.category is:

  v.category input=river_net2 option=report
Layer: 1
type       count        min        max
point          0          0          0
line      102092          1     102072
boundary       0          0          0
centroid       0          0          0
area           0          0          0
face           0          0          0
kernel         0          0          0
all       102092          1     102072
Layer: 2
type       count        min        max
point          1          1          1
line           0          0          0
boundary       0          0          0
centroid       0          0          0
area           0          0          0
face           0          0          0
kernel         0          0          0
all            1          1          1
Layer: 3
type       count        min        max
point          1          1          1
line           0          0          0
boundary       0          0          0
centroid       0          0          0
area           0          0          0
face           0          0          0
kernel         0          0          0
all            1          1          1

At this point, I visually confirm that both points are connected to the 
network and then run:

v.net.distance in=river_net2 out=river_path from_layer=2 to_layer=3 
--overwrite

However, I (keep) get a warning ( WARNING: 1 'from' feature was not 
reachable) and the output is empty. I have read a few posts online 
reporting the same issue, but none of the proposed solutions have 
helped. Is there a step that I am overlooking as I would have assumed 
that once the network topology is built and the points are connected to 
the network that it would have run correctly. I confirm that I can 
calculate the shortest path when I use a start point that is the river 
network (excluding the stream), so I am assuming that the issue is 
related to the output of the v.patch?


Thanks in advance for any help or suggestions.

best regards,

Daniel.

[1]: https://grass.osgeo.org/grass76/manuals/v.net.distance.html