Network Analyst Questions ... and congratulation!

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02-25-2010 05:43 AM
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Occasional Contributor III
Hi,

doing tests with newly build networks that have been dissolved with the new tool makes me say: Great speed improvements, thanks!

To make me use that more efficiently in the workflow, please answer my following questions:

- There is also a new GP tool called SORT that could be used to sort i.e street edges in a FC before adding them to a network ... will that improve the network or does Dissolve take care of this in itself when creating the hyper-edges?

- It seems that Dissolve drops any attributes from the tables that are not used in Network Attributes - can that be avoided?

- What is the influence of Dissolve and/or Sort on the features Object-IDs ...since they are used as references i.e. by SignPosts and Turns ... will ObjectIDs remain unchanged if Turns/Signposts are there?

Thanks and regards
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New Contributor III
Glad to hear that the speed improvement has helped you!


- There is also a new GP tool called SORT that could be used to sort i.e street edges in a FC before adding them to a network ... will that improve the network or does Dissolve take care of this in itself when creating the hyper-edges?


The Dissolve Network tool spatially sorts your street features.  There is no need to use the GP sort tool to sort a dissolved network and using the GP sort tool on a network will reorder your streets and change OID values (breaking any turn/signpost features that reference the old OIDs).



- It seems that Dissolve drops any attributes from the tables that are not used in Network Attributes - can that be avoided?


This cannot be avoided.  The Dissolve Network tool merges like street features to create larger street features so that the network build algorithm can create hyper-edges.  While dissolving features the tool maintains the correctness of field values that are used as network attributes.  If an attribute is not a network attribute then the tool does not know how to merge field values to produce a correct field value on the dissolved feature and so we simply remove non network dataset related fields from the output streets feature class as the only other option would be to output incorrect values.



- What is the influence of Dissolve and/or Sort on the features Object-IDs ...since they are used as references i.e. by SignPosts and Turns ... will ObjectIDs remain unchanged if Turns/Signposts are there?


The Dissolve Network tool will update all OIDs used as foreign keys in turn feature classes, signpost feature classes, and historical speed tables.  This tool will create duplicate copies of your turns, signposts, and historical traffic tables and these duplicated tables reference the correct dissolved OID.  Your dissolved network will correctly use these network attributes (once you build it).  There is no need for you to update your OIDs unless they were incorrect in the original network dataset.

The standard GP Sort tool does not maintain any OIDs so you should not use it on network datasets that have turns, signposts or historical traffic.  You certainly can use the standard GP sort tool on feature classes that are frequently used as inputs to Network Analyst problems (e.g. point addresses in a nation).

Please feel free to ask if you have any other questions about this tool.
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Occasional Contributor III
Thanks for the replies - saves time!

To keep attributes I can just create simple descriptors ... Just two more findings i'd like to report

- Dissolve will fail, if the involved FeatureClasses do not have the shape-length-field as the last field in the field order. I've seen that with "sort" in early stages. The workaround is to copy the feature-class (or in my case the whole network dataset in its Feature Dataset) once - since that will re-order the fields. But smarter would be s solution where custom fields at the end of the table are acceptable.

- I tried to run dissolve twice on the same network (less attributes - faster net), after changing some settings - and this failed, apparently because the Override Point feature class name is hardcoded and not variable. If I rename it I can re-run dissolve ... maybe the tool should be smart enough to change the Override Point Feature Class name, if the pre-set name is already taken.

Regards
Guenter
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