We need to be able to identify wells

[timlinux]

Problem

Given a line layer, identify by selection all wells (points with no upstream nodes)

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 well
• Implement logic that determines wells on the network based on the logic (in pseudocode):

IF upstream_node_count == 0 AND downstream_node_count > 0
THEN
    well = True
ENDIF

The logic here being that if there is no upstream node and there is more than zero downstream node, so this node must be the origin of the water supply for this river segment.

• select all line features in the river layer whose starting node is a well
• overlay the nodes layer on the river layer with wells clearly symbolised (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 well and populated with 0 if the node is not a well and 1 if it is.
• The line layer should have all segments selected whose origin node is a well selected
• The user should be able to easily visually identify all segments whose origin node is a well

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

id	upstream_node_count	downstream_node_count	well
1	0	1	1
2	2	3	0