topic Re: Intersect v/s Union in Spatial Data Science Questions

Intersect v/s Union

YusufMohamedshah — Fri, 18 Sep 2015 14:51:13 GMT

I am new to ArcGIS. I am trying to use Linear Referencing Tool: Overlay Route Events. I have two dbf files: One is a line file and another is a point file. I want to do an overlay of point file to line file and get the results as a UNION. But I get an error. However if I do INTERSECT it works fine.

So the question is: Why an INTERSECT works but UNION does not work. If I want the results as UNION, is there a work around.

I would appreciate any input.

Thanks

Re: Intersect v/s Union

TimWitt2 — Fri, 18 Sep 2015 14:54:06 GMT

Union does not work with a point or a line feature. It only works with polygon features.

What is the goal of doing what you want to do? That might help us to help you.

Re: Intersect v/s Union

RebeccaStrauch__GISP — Fri, 18 Sep 2015 15:30:33 GMT

You may want to take a look at the Near command

Near—Help | ArcGIS for Desktop

This can add an XY coordinate of the closest point on the line feature. If you intent is to have the point on the line (not sure that it is), you could create a script to move the location to the new coordinates, or create a new featureset using the new coordinates.

Re: Intersect v/s Union

YusufMohamedshah — Fri, 18 Sep 2015 15:38:35 GMT

I am working with highway data. I have two files: a roadway centerline file in which each segment is identified by RouteID, FromMeasure and ToMeasure. And a roadway signs file in which each sign is identified by RouteID and FromMeasure. My goal is to locate the signs on the roadway and produce an output file with all the roadway segments with signs info attached. Hence I wanted to do UNION so that I can get all the roadway columns as well as Signs columns in the final file.

Thanks

Re: Intersect v/s Union

TimWitt2 — Fri, 18 Sep 2015 15:40:32 GMT

You could create a spatial join ArcGIS Desktop

Re: Intersect v/s Union

NeilAyres — Fri, 18 Sep 2015 15:46:03 GMT

Sorry, files???

Is this spatial, well at least the roadway center lines?

If you have roadway centerlines as a feature class with measures (PolylineM), then you can join the signs table to it by creating route events. This problem has nothing to do with union or other geometry overlay operations.

Re: Intersect v/s Union

YusufMohamedshah — Fri, 18 Sep 2015 15:50:15 GMT

The spatial join has option of using only one common column name between the two tables. I need following logic to get the output:

If RouteID between the two files match and FromMeasure from Signs fall between FromMeasure and ToMeasure from Roadway then output. Also break the segment where the match takes place. So for example if a segment has two signs, the segment should be broken at the points where sign matches. So there will be three segments with same RouteID and updated FromMeasure and ToMeasure.

Re: Intersect v/s Union

YusufMohamedshah — Fri, 18 Sep 2015 15:57:42 GMT

Thanks Neil for your reply.

I am new to GIS world hence I am not using correct language. I have two dbf tables: Roadway which is line data in which each segment is identified by RouteID , FromMeasure and ToMeasure and a Signs table which is point data in which each sign is identified by RouteID and FromMeasure. My goal is to locate the signs on the roadway segments and produce an output file with all the roadway segments along with signs. Also whenever a sign matches the roadway segment it should be broken at that point by creating a new FromMeasure and ToMeasure.

Thanks

Re: Intersect v/s Union

DanPatterson_Retired — Fri, 18 Sep 2015 15:57:54 GMT

So your data are in the form as noted here

http://desktop.arcgis.com/en/desktop/latest/guide-books/linear-referencing/about-overlaying-event-data.htm#GUID-DF53F6FE-7E53-46D5-B2EC-06FED79ECC9F

and you were doing this...

http://desktop.arcgis.com/en/desktop/latest/guide-books/linear-referencing/overlaying-events-intersecting-or-unioning-events-.htm

and from here...

http://desktop.arcgis.com/en/desktop/latest/tools/linear-ref-toolbox/overlay-route-events.htm

did you see this paragraph?

If either the input or overlay event properties are type POINT, the output event properties must be defined as type POINT when an INTERSECT overlay is performed. The output event properties must be defined as type LINE when a UNION overlay is performed.

and what was the error

Re: Intersect v/s Union

YusufMohamedshah — Fri, 18 Sep 2015 16:07:18 GMT

Following is the screen capture of the Overlay Route Events tool: When I execute it I get the error shown below:

Re: Intersect v/s Union

DanPatterson_Retired — Fri, 18 Sep 2015 16:22:43 GMT

Ok...saw the screen shot (keep trying to attach it, it may be too large) you sent.

I don't see anything obvious, although I don't like the paths that you are obtaining your data from or saving it to, but if it has worked in those streams before, it rules those out. The error is too generic, it could be there are some bad values in one or both of the tables and you may want to untoggle the zero length option. If it works with other data sets, then it may lie in the data...you could try a subset for a small known area that you can examine and see if it works for the subset.

Re: Intersect v/s Union

ChrisDonohue__GISP — Mon, 14 Dec 2015 16:13:31 GMT

Adding Richard Fairhurst as he may have ideas.

Chris Donohue, GISP

Re: Intersect v/s Union

RichardFairhurst — Mon, 14 Dec 2015 16:57:46 GMT

The screen shot is consistent with what Dan pointed out, you cannot use Union when one of the event tables is a point event table. Notice that the output event type setting is Line and that setting cannot be edited to change it to Point. You can only create points when a point event table or feature class is used with any of the Intersect tools and points simply don't work with any of the Union tools.

The workaround is to create two new fields to hold duplicates of the real measure fields of your line events. You should use the duplicate line measure fields for the inputs to the tool. Do an Intersect with the points, not a Union. Make sure the output measure field name is not the same as the original measure field names used by the line events. The output will have a new measure field for the sign point location created by the tool, but it will also have the original measure fields.for the line. Just use the two measure fields preserved from the line that were not inputs to the tool to create a line event layer. The layer will contain line events with the original line data combined with the data of one of the signs it touched, and there will be overlapping lines that will match the full set of signs touched by each segment.

In case what you really want is a single line event that has many columns of fields that combine the data for each and every sign along the segment into a single event, no tool does that. A Pivot table could pivot one of the sign attributes into multiple columns from the output of the Intersect above, but it would not pivot multiple point attributes without a lot of effort.