topic Re: Polygon - Dissolve; leaves "cracks" in the polygon feature in Geoprocessing Questions

Polygon - Dissolve; leaves "cracks" in the polygon feature

denisedavis — Fri, 29 Apr 2011 11:09:54 GMT

I have hundreds of polygons that I'd like to put together to create one polygon. In the past I would simply use the Dissove tool and this worked fine. The polygons I'm trying to put together now are parcels and they are separated wherever there is a road right-of-way. When I do the Dissolve, the polygon has "cracks" in it. I've gone through most of the tools I thought might get rid of the "cracks" (Eliminate, Integrate, Union) and can't seem to get a solid polygon feature. Any help with this is greatly appreciated. Thanks in advance!

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

JohnSobetzer — Fri, 29 Apr 2011 12:26:07 GMT

You might:

1. run a repair geometry (after saving a backup).
2. run a clean
3. if you only have a few of these you probably could select them in an edit session, modify feature and delete the vertices.
4. if have ArcInfo use feature to lines and if there are any "crack" lines delete them, then run feature to polygon.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

DanPatterson_Retired — Fri, 29 Apr 2011 12:53:06 GMT

if hundreds to one is what you want, have you tried the following
1 estimate/measure the gap between the polygons to get some sense on the space you need to close (ie say 10 meters)
2 buffer the polygons using the dissolve option, using a buffer width slightly larger than your estimated gap in 1 (say 5.1 meters). At this stage you should have one big polygon with no gaps.
3 negatively buffer the result in 2 ( ie -5.1 meters)
This should hopefully, but no guarantee return what you want, but this will depend upon the polygon configurations prior to the initial buffer.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

TimothyHales — Fri, 29 Apr 2011 12:54:45 GMT

Note sure if this will get you to your expectations, but open an edit session and select all of the features. Then use the merge function from the editor menu. This will take all of the feature and create a single multipatch feature. If you then would like for them to be individual features you can use the Multipart to Singlepart tool.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

denisedavis — Fri, 29 Apr 2011 13:16:27 GMT

Thanks for all the responses. I've tried everything suggested except for the buffer that Dan suggested. This works well aside from the rounding of the edges. I'm working in ArcGIS 10 with an ArcInfo license. The option to make the corners flat/squared is grayed out so I'm not able to change it in the Buffer Geoprocessing pop up form. Any suggestions as to how I could get my straight edges back after the buffer is appreciated. And thank you again for everyone's help!

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

DanPatterson_Retired — Fri, 29 Apr 2011 14:35:43 GMT

did you perform the negative buffer? after the initial buffer?

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

denisedavis — Fri, 29 Apr 2011 17:10:13 GMT

Oh yes. And it worked Great! Except for the rounding of all the edges. Do you know how I can get the option to change the edges in the geoprocessing tool from rounded to flat/straight?

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

DanPatterson_Retired — Fri, 29 Apr 2011 19:06:25 GMT

As indicated in my original thread

but this will depend upon the polygon configurations prior to the initial buffer.

the outcome would depend upon the original polygon configuration. do you have any images of pre-buffer...buffer and ... negative buffer that demonstrates your situation. It may be a case of getting too exhuberant in your buffer values, both positive and negative...and it might take a few passes to obtain what you want. So pictures would help along with gap details and buffers used.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

DonovanCameron — Fri, 29 Apr 2011 21:16:59 GMT

In the thread, 'filling in' spaces between polygons, that post suggests using the Feature to Polygon tool with a defined cluster tolerance.

Might work for you since you are dealing with lots of Right of Ways with a similar gap distance.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

denisedavis — Mon, 02 May 2011 12:17:34 GMT

So pictures would help along with gap details and buffers used.

I've attached a .docx with images. I've tried different buffers and I'm still not getting the option to keep the squared corners. Perhaps there is a setting I'm not aware of so I can reset the default (rounded edges) to squared. I'll look into this, but if anyone knows where this setting is and can help me out, I'd appreciate it.

Thanks again for all your help.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

denisedavis — Mon, 02 May 2011 12:28:02 GMT

'filling in' spaces between polygons[/URL], that post suggests using the Feature to Polygon tool with a defined cluster tolerance.

Thank you. I looked at the post before I started this thread.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

JohnSobetzer — Mon, 02 May 2011 17:00:15 GMT

I misunderstood what your problem was. I thought it was topological slivers or "debris".

If you have ETGeowizards You might take the results of your negative buffer and use the global snap on it to your original polys. You might try different distances. It isn't one of the free tools, however, and I don't know if you can find something equivalent.

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

denisedavis — Tue, 10 May 2011 17:10:09 GMT

In the thread, 'filling in' spaces between polygons, that post suggests using the Feature to Polygon tool with a defined cluster tolerance.

Thanks Don. Yes, I have tried this tool and it would work if the ROW had a consistent width. I was able to make Dan's suggestion (large buffer and then negative buffer of the same size) work except for retaining right angles on corners. There is an option in the buffer dialog that offers a drop down for which type of edge you desire. This option ("End Type") was grayed out so I wasn't able to change "Round" to "Flat". This option is not available when there are multiple polygons selected. If there is anyone who knows of a setting to make the "Flat" choice available when multiple polygons are selected, I would appreciate knowing where it is.

Thanks again for all the help!

Re: Polygon - Dissolve; leaves "cracks" in the polygon feature

DanLee — Wed, 18 May 2011 15:35:16 GMT

The Buffer process (positive and then negative values) will leave those undesired shapes at corners and turns, as shown in your images. You can try Aggregate Polygons with the ORTHOGONAL option and an aggregation distance a bit larger than the gaps.

Thanks,