Network connectivity issue

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04-22-2013 09:36 AM
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New Contributor
Hi All,

I have a road network, completely built and working fine. However, when I solved a route (using shortest path), I realised that the solution given was not the shortest path. The shortest path was crossing over a bridge but my solution avoided the bridge and went a long way to reach the destination. When I checked the road edges using the "Network Identify Tool", the road segment which is supposed to be adjacent to the bridge is adjacent to the road segements passing below the bridge.

I want to change the connectivity of this road segment by removing its connectivity with the road segments passing below the brige and establish connectivity with the bridge. I have attached a word document with a diagram illustrating the issue.

Thanks
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Esri Contributor
Hello Habtom,

It sounds like you have elevation fields set up on your network dataset, but the elevation values aren't matching the way they should. If you go to the Network Dataset Properties dialog box > Elevation tab, the Using Elevation Fields radio button should be enabled if elevation fields are enabled. (If they weren't enabled, you would probably get connections among all the adjacent lines rather than a subset of them.) There should also be two fields listed in the table below the radio buttons, which I'll refer to as the elev fields.

Add the source streets feature class to the map and set the symbology to "Arrow at End" to easily see where the to-side (and thus the from-side) of a line is.

Use Identify or look at the attribute table to figure out whether the from- and to-ends of the lines have appropriate values. You want roads that connect to have the same elevation values on the ends where they touch. So, for instance, if we assume the lines in your diagram are digitized in the direction of the blue arrows, we would want something like the following:


  • To Z-elevation of Line B-C: 0

  • From Z-elevation of Line C-D: 0

  • To Z-elevation of Line E-C: 1

  • From Z-elevation of Line E-C: 1

This way B-C and C-D connect to one another but not to E-C or C-F.
And E-C and C-F connect to one another.
Note that if B-C and C-D are above the other lines, you may want to set their connecting elevation values to be 1 and switch the E-C values from 1 to 0 for easier interpretation, but it doesn't really matter for it to work properly.

The help files probably do a better job of explaining this than I just did. So you might also want to take a look at the Modeling Elevation section in the following topic:
http://resources.arcgis.com/en/help/main/10.1/#/Understanding_connectivity/004700000009000000/

Thanks,
Robert

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Esri Contributor
Hello Habtom,

It sounds like you have elevation fields set up on your network dataset, but the elevation values aren't matching the way they should. If you go to the Network Dataset Properties dialog box > Elevation tab, the Using Elevation Fields radio button should be enabled if elevation fields are enabled. (If they weren't enabled, you would probably get connections among all the adjacent lines rather than a subset of them.) There should also be two fields listed in the table below the radio buttons, which I'll refer to as the elev fields.

Add the source streets feature class to the map and set the symbology to "Arrow at End" to easily see where the to-side (and thus the from-side) of a line is.

Use Identify or look at the attribute table to figure out whether the from- and to-ends of the lines have appropriate values. You want roads that connect to have the same elevation values on the ends where they touch. So, for instance, if we assume the lines in your diagram are digitized in the direction of the blue arrows, we would want something like the following:


  • To Z-elevation of Line B-C: 0

  • From Z-elevation of Line C-D: 0

  • To Z-elevation of Line E-C: 1

  • From Z-elevation of Line E-C: 1

This way B-C and C-D connect to one another but not to E-C or C-F.
And E-C and C-F connect to one another.
Note that if B-C and C-D are above the other lines, you may want to set their connecting elevation values to be 1 and switch the E-C values from 1 to 0 for easier interpretation, but it doesn't really matter for it to work properly.

The help files probably do a better job of explaining this than I just did. So you might also want to take a look at the Modeling Elevation section in the following topic:
http://resources.arcgis.com/en/help/main/10.1/#/Understanding_connectivity/004700000009000000/

Thanks,
Robert

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Thanks Robert. I manage to edit the elevation values and it worked.

Thanks

Habtom
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