We need to be able to identify pseudo-nodes

[timlinux]

Problem

Given a line layer, identify by selection all pseudo-nodes (points one upstream node and one downstream node)

Proposed solution

The implementation should take the following steps:

• extract nodes with basic metadata (upstream count, related line id, related nodes etc.) as per #8
• add an attribute to the node table that indicates if a node is a pseudo-node
• Implement logic that determines pseudo-node on the network based on the logic (in pseudocode):

IF upstream_node_count == 1 AND downstream_node_count == 0
THEN
    pseudo-node = True
ENDIF

The logic here being that if there is one upstream node and there is one downstream nodes, so this node must be a pseudo-node (a node that can be omitted)

• select all line features in the river layer whose starting node is a pseudo-node
• overlay the nodes layer on the river layer with pseudo-nodes clearly symbolized (client to provide appropriate symbology, in the mean time we can just make up our own visual vocabulary).

  Expected outcome

• The extracted nodes layer should have a column added called has_pseudonode and populated with 0 if the node is not a pseudo-node and 1 if it is.
• The line layer should have all segments selected whose origin node is a pseudo-node selected
• The user should be able to easily visually identify all segments whose origin node is a pseudo-node

Example nodes attribute table (excludes other extracted feature types):

id	upstream_node_count	downstream_node_count	has_pseudo-nodes
1	1	1	1
2	2	3	0