Network Dialog question

[wayne]

I looked at the help for the Network Dialog box: TopoFusion Help.  I also searched this forum on "Network Dialog" and didn't find what I was looking for.

I know the method is proprietary, but can you explain what each individual sliders is?  You only have a joint explanation that makes sense when you know the answer already, but doesn't

Quote

The slider bars for reduction and contraction strength control how close or similar sections of tracks must be in order for them to be considered duplicates. Larger values will result in tracks being considered the same (and subsequently averaged together) when they are further apart.

I'm guessing here:
• Reduction:  How close two tracks have to be to each other to reduce them into a single track?  (NOT the reduction of total number of points)

• Contraction: How close single points have to be (without a lot of X-Y change) to reduce them to less points.
Ex: -  -  -  - - - -
could be contracted to:  - ____ -
with no loss of information.  (underscore added to keep spacing)

• Or I might be wrong and the program doesn't reduce points (except overlaps) at all.

Either way, a more detailed explanation of what each bar's function is would be appreciated.  Thanks.

[Krein]

Hi Wayne,

Actually the network algorithm is not proprietary.  The user manual needs to be updated in that regard.

Go here:

http://topofusion.com/network.php

We published a paper about the technique, but it may be a little hard to dig into.

Reduction strength is a measure (in meters) how how close parallel tracks must be to each other in order for them to be considered the same trail.  They are then reduced to one track.

Contraction strength is a bit different than what you're thinking.  The network algorithm does not reduce the number of points.  A contraction is a "spur" in the network (maybe due to going off the trail to fix a flat, or to look at a view point) that isn't really a trail.  Sometimes they come about in the process of reduction.  Contraction strength means any trail segment with distance less than the slider value (in meters) will be deleted or merged into the network.  It's deleted if it's a spur; merged if it's a link between two nodes in the graph.

Hope that helps.  Feel free to ask further questions.

[wayne]

Thank you.  I would suggest you include your above information in the on-line documentation.

The new definition of Contraction explains why my 'stubs' were disappearing.  I make stubs on purpose, to show where another trail is to follow up on later.  Most of my stubs seemed to be long to avoid elimination, but a few of the shrunk down in size (but didn't get eliminated).

[Krein]

Quote (wayne @ Feb. 20 2007,3:01)

Thank you.  I would suggest you include your above information in the on-line documentation. The new definition of Contraction explains why my 'stubs' were disappearing.  I make stubs on purpose, to show where another trail is to follow up on later.  Most of my stubs seemed to be long to avoid elimination, but a few of the shrunk down in size (but didn't get eliminated).

Yep, I updated the manual a bit just now.  Thanks for pointing this out.

The stubs will often get shrunk down, yep.  As long as they are reasonably long, they'll stay around, though.