topic Re: Snapping problem causes wrong network dataset creation in ArcGIS Network Analyst Questions

Snapping problem causes wrong network dataset creation

EleniBoboti — Wed, 29 Jun 2011 17:08:35 GMT

Dear colleagues,

I am facing a problem that I cannot solve and would like to ask you for any ideas.

I want to create a network dataset from digitized road features. I digitized the features myself from a scanned map making use of the snapping option in the Editor.
However the nodes of my edges do not snap properly to the other edges. They appear to be snapping correctly at first but when I zoom in, there is still a gap (see attached picture: [ATTACH]7553[/ATTACH]). Thus in the network dataset edges do not get properly connected either.

Now I've tried a way to get around that which was not successful:
It seems the snapping is connected to the XY Tolerance which one can set, when creating a feature data set. By default the tolerance is set to 0.001 meters. So below 1 mm distance coordinates are considered to be equal. Hence the snapping goes somewhat wrong. There is always 1 mm distance between the node and the edge like in the picture.

So I changed the XY Tolerance to 0 in the feature data set. Then I used the Integrate tool on the road features with a tolerance of 0.002. Now all the nodes which were 1mm appart from the edges now appear to have snapped to the edges. However much I zoom in now, I cannot see a gap any more. Nevertheless the network dataset generation still does go wrong. There still seems to be a tiny little gap between the nodes and the edges.

My question is now. Is there a way to set an XY Tolerance for the network dataset generation or is there a way to snap the nodes correctly to the edges?

Any suggestion is appreciated!

Thank you so much.
Eleni

Re: Snapping problem causes wrong network dataset creation

JaySandhu — Wed, 29 Jun 2011 19:19:30 GMT

When you create the network dataset, what connectivity model did you choose: End Point or Any Vertex?

If it is End Point, then you will not get the node to connect to a middle of an edge as shown in your picture.
In that case, switch to Any Vertex and re-build your network.

Regards,
Jay Sandhu

Re: Snapping problem causes wrong network dataset creation

JoeBorgione — Thu, 30 Jun 2011 11:00:38 GMT

When you create the network dataset, what connectivity model did you choose: End Point or Any Vertex?

If it is End Point, then you will not get the node to connect to a middle of an edge as shown in your picture.
In that case, switch to Any Vertex and re-build your network.

Regards,
Jay Sandhu

Jay- as many of my posts indicate, I'm not a fan of 'Any Vertex' connectivity. But there has to be a reason that this option is available: When is Any Vertex connectivity advantageous to End Point connectivity?

All the best-

Re: Snapping problem causes wrong network dataset creation

JaySandhu — Thu, 30 Jun 2011 16:48:48 GMT

Joe,

Any vertex connectivity maybe useful if all your data was planar. In that case you could maintain some longer roads without breaking them at every T intersection. Some data formats such as the the Open Street Map are built using this model. However, it is not a good choice for non-planar data such as highway intersections with ramps, underpass, overpass situations as Integrate will put a vertex on these overlapping and crossing lines and then the Any Vertex connectivity will connect them!

it is just another connecivity model and if data comes that way, we support it!

Jay Sandhu

Re: Snapping problem causes wrong network dataset creation

EleniBoboti — Thu, 30 Jun 2011 16:59:24 GMT

Dear Jay,

Thank you very much for your useful information. Since my data is planar the 'Any Vertex' option solved my problem and so I can now use my network dataset.

Kind regards,

Eleni

Re: Snapping problem causes wrong network dataset creation

EleniBoboti — Sun, 03 Jul 2011 12:41:19 GMT

Dear Alan,

Thank you for your explanation, it definitely helped me understand the situation a bit more. However, I still do not understand why I have to use the Integrate tool to my features before generating my network dataset. Even if I set a higher tolerace (like 0.002) to my original dataset and then generate the network dataset, there are no connections. Even if the nodes are only 0.001 m away from the edges. Shouldn't it work without using the integrate tool?

Kind regards,

Eleni

Re: Snapping problem causes wrong network dataset creation

JoeBorgione — Mon, 04 Jul 2011 11:02:46 GMT

Dear Alan,

Thank you for your explanation, it definitely helped me understand the situation a bit more. However, I still do not understand why I have to use the Integrate tool to my features before generating my network dataset. Even if I set a higher tolerace (like 0.002) to my original dataset and then generate the network dataset, there are no connections. Even if the nodes are only 0.001 m away from the edges. Shouldn't it work without using the integrate tool?

Kind regards,

Eleni

Eleni; the integrate tool actually moves feature elements (vetexes in you case) to become absolutely coincident with others found within the snapping tolerence. Is it possible for you to post a portion of your data with known inconsistencies here on the forum? I would be happy to execute the integrate tool upon those features to see if I can recreate the issue you are having.