11/13/2009 2:44:55 PM
MJ
Posts: 14
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Hello
I sometimes get the following error when carrying out a network accessibility calculation (see attachment).
The message appears during the calculation process when the road network data appears to be loading in. If I press okay the calculation continues and the results I obtain seem fine.
If it is relevat, the road data I am using is NavTeq and is clipped from a dataset I have in ArcGIS. This dataset has been merged by our GIS manager to contain all roads in one layer.
Anyone know how to avoid this error and if it is actually a problem?
MJ
edited by MJ on 11/13/2009
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11/16/2009 2:31:06 PM
GlosCC
Posts: 2
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Hi
This message only appears when the option to add additional nodes has been selected. I've always just pressed ok and ignored it.
SL
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11/16/2009 2:44:47 PM
admin
Administrator
Posts: 146
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This is to do with too many road nodes, Accession will put Road Nodes in by default at any junction or at the start and end of the road. By selecting increase road accuracy it will but additional nodes at the specified distance. If you put too many nodes on the screen/select too small a distance then you will get this error message. I would suggest increasing the distance of Road Node spacing during the calculation.
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11/23/2009 10:12:20 AM
MJ
Posts: 14
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Thanks,
But I am only using the default setting of 200m. I will try increasing this in future and see what happens.
Do you think it has any implications for the results produced ignoring this message? I.e. Is the road accuracy being increased at all if this problem occurs or is the increase in the number of nodes only partial? Also, is it something to do with using a very large amount of road data for the calculation.
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11/23/2009 1:02:53 PM
admin
Administrator
Posts: 146
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If the road network is really large then it could just be that there are too many nodes for Accession to deal with, I would suggest trying to increase it too 250 or 300m. If the road is very detailed and has a lot of existing nodes then you can get away with not using the "increase road accuracy"
As for when the error message returns, I believe that there is an error adding additional nodes, so you may find that some areas could show poorer accessibility if they live further away from a road junction. Apart for this there should not be any issues.
Regards,
Dan
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7/3/2010 12:00:57 PM
carol birchall
Posts: 17
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Hi Dan,
Just to follow on from this ... how many nodes is too many, or rather what is the max number that Accession can cope with? And also just to clarify, are you saying that the error message appears when the max has been reached but by clicking on OK the calculation will continue but without adding any more nodes?
Carol
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7/5/2010 9:49:53 AM
admin
Administrator
Posts: 146
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Hi Carol,
Unfortunately it's not really known what the maximum number of nodes are, this is because the number can vary depending on the computer performance and size of the network.
You're correct, if the error message appears then the calculation will complete but new additional nodes will not be created. The best suggestion is to re-run the calculation with a higher value in the "increase road accuracy" option.
Cheers,
Dan
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