How would you detect such a cargo? Note that cargo itself has no "this is primary" property. You only know industries, and what it accepts and produces.
Bulk class can be such (roughly approximated) criterium, however even in case of primary cargo, cargodist itself sometimes is useful, sometimes not.
For example, consider following chain:
S1 ---> R1 <--- S2 ---> R2 <--- S3
Cargodist will send some freight from S1 trough R1 and S2 to R2, and the same with S3 to R1.
It is not bad, because your vehicles have no empty runs. And load time at S2 is low.
OK, I want to enable cargodist even for bulk/primary cargos.
But consider same topology located not linear:
R1 <-- S2
| R2 <-- S3
and now S1-R1 link is used for wastage S1-R2 cargo instead of profitable S1-R1 and S2-R2 ones.
It is a reason, why players on my server requested to switch freight cargodist off.
I fairly regularly see odd routes for airplane trips that are way longer than necessary.
But those discounts are intentionally provided by airlines operators - as Kamnet mentioned, it is to avoid empty links.
You cannot buy cheap A1-B-A2 ticket if A1-B link is already saturated.
In case of openttd, fares are fixed, and cargodist make totally opposite thing -
it assign unprofitable A1-B-A2 instead of profitable A1-B.
The real company would bankrupt within a days with such fares policy.
I understand, that cargodist authors are willing to force players to make optimal transport grid,
but such feature described above seems to be to much harassment, especially for on-line players -
there is no opportunity to pull-down, and analyse every cargo at each station.
My compromise proposition is as follows:
lets keep demands calculation as it was before
, but give load priority
for links which direct distance to hop distance ratio is higher.
(it can be soft priority - just decrease amount of "unwanted" cargo loaded proportional to distance ratio).
If you have spare place in your vehicles, those "unwanted" cargos would be transporter either.
If all loading space is filled up by cargo travelling straightforward, roundabout cargo would pile up at station.
I think it is clear information for player, that his network is suboptimal, without stealthy abusing his resources.
My experimental openTTD server: 220.127.116.11:3979 non-standard client, now testing: JGRPP http://tiny.pl/ggnch
Projects: Reproducible Map Generation patch
, NewGRFs: Manpower industries, PolTrams, Polroad, 600mm narrow gauge, preindustrial houses, wired, ECS industry extension, V4 CEE train set
Addicted to freeciv longturn.