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How to achieve best results from Align Features geoprocessing tool?

DavidSchuster

Good afternoon!

I'm trying to align a feature class containing traffic jam polylines with our road network in an automated way. The traffic data provider uses a different road network than ours, hence the need to align them.

For the most part the Align Features geoprocessing tool works quite well, except that sometimes it gets confused where roads converge at small angles (for example where entrance/exit ramps meet the main roads/service roads) and at complex highway interchanges or roundabouts.

In troubleshooting this issue, it seems that the spatial index grid size might have some effect on the alignment results. Somewhat by accident, I noticed that if I take the same input geometries, and align them with the same target geometries (repeating the test using target feature classes with different spatial index grid sizes), one resulted in a correct alignment and the other did not. I repeated the test in ArcGIS Pro 3.1 and in ArcMap 10.8.2 and I get the same results.

Can anyone help me figure out how to achieve the best results from the Align Features tool? Would using a larger or smaller grid size help, or is it completely coincidental?

Or is there a better way to achieve what I'm trying to do?

Thank you!

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DavidSchuster

Dan, thank you very much for taking the time to run tests using our sample data and for meeting with me last week! I'll try to summarize everything I've learned so far from our conversation and my experiences:

To recap, the Align Features tool was not designed for my specific use case of aligning traffic jam lines from a 3rd party vendor to a our independent road network. It's meant more for boundary alignment where the entire feature is present in both the input and the target feature classes. Despite this, I found that it still does a great job in many cases. For our situation, we knew it wasn't realistic to expect anywhere near 100% correct alignment for all the traffic jams, but this was OK as we were looking for progress, not perfection. Most of the major traffic jams we care to include occur on straight, divided roads that Align Features had little problem handling correctly. So this tool still works for our purposes.
The Align Features tool can get confused by things like roundabouts, entrance/exit ramps, highway interchanges, etc. It helps to provide the Align Features tool with a match field (such as road name or road classification) assuming you have such a field in both the input and target feature classes. In our case we did not have a matching field in both our road data and traffic jam data, so we had to go through extra preprocessing steps to generate one.
Some of the complex areas of the road that we couldn't handle correctly simply had to be excluded from traffic jam processing.
The traffic jam data we receive sometimes contains overlapping lines, so it was also necessary to handle these situations. Some of these overlaps represented the traffic in opposing directions of an undivided road. Other overlaps we couldn't explain and we'll need to work with the traffic data vendor. I haven't quite solved this problem yet, but I'm looking at the Spatial Join, Group By Proximity, and Dissolve tools to hopefully resolve these.
In order to identify problems and improve our process, I added steps to our model to cross check the results of the Align Features tool with the road network to find any places where the alignment failed (via the Intersect and Symmetrical Difference tools). The AF_CONF (confidence) field produced by the Align Features tool was helpful as well in some case.
Processing time can be lengthy on large datasets, and since we're dealing with real-time traffic, time is of the essence. We want the model to be as fast as possible. So we're trying be smart about what we pass into the Align Features tool by limiting the number of features in the input and target feature classes.
Dan, there were some test cases that you identified where it seems like the align tool should have worked but didn't. From what I understand you are planning to look into those for possible future fixes/enhancements. One other enhancement that would be great if possible is the option to "Maintain curve segments" so that the Align Features tool can output true curves wherever the alignment target was a true curve segment. To retain true curves, I'm doing some post processing steps using the Pairwise Clip tool which has an environment option to maintain curve segments. Just a suggestion.

Hopefully this summary is helpful to others that might be attempting to use Align Features in the same way.

Thank you again for your help!

-David

DanLee

Hi David, I did some testing and would like to show you a few good / bad cases. Also I had to do some pre-processing before using Align Features. Would you like to email me at dlee@esri.com so I can explain more to you? Once you get a clear conclusion, you can sum here.

DavidSchuster

Thanks Dan - btw, I'm sorry, the project only has one batch of jams (I thought there were more batches), but it should be plenty to give you the idea of the type of geometry we're getting for the traffic jams.

DanLee

Got it right this time. Thx!

DavidSchuster

Strange, I'm reattaching the new ppkx file to this post. It should look like this:

SampleRoadsAndTrafficJams.ppkx

DanLee

Yes, I extracted the ppkx you shared. Here are the data I got:

DavidSchuster

Dan, did the new ArcGIS Pro package attachment (SampleRoadsAndTrafficJams.ppkx) that I posted today come through? That one has more batches of jams as well as the complete set of target roads.

Thanks,

David

DanLee

Hi David,

Thanks for sharing the sample data. I see the 135 features in TrafficJamLines_All_Backup, but I can not find the target features you want to align to. Could you share the target features please? Thx.

DavidSchuster

Hi Dan,

Attached is some sample data containing several batches of traffic jams (each representing the traffic jams at a different point in time), as well as the target roads I'm trying to relate them to.

The jams are coming from a provider with a totally different road network, so we expect there will be times when the jams are just too different to be aligned properly, so I'm certainly not expecting anywhere near 100% success rate. The Align Features tool seems to do a really good job - it just gets confused sometimes (as mentioned in my original post). I've experimented with different ways of building the model to improve performance and also deal with other issues I've encountered along the way (such as true curves). I noticed that the Align Features tool does not have a environment setting for "Maintain Curve Segments" similar to the one offered by Pairwise Clip, where the output of aligning to a true curve segment would be a true curve segment.

If you have any information you could share about how Align Features works "under the hood" that might help me to avoid some pitfalls. Any suggestions you might have for alternative approaches are much appreciated as well. Some of our key requirements are that it has to be automated as a geoprocessing task and it needs to run quickly (preferably < 30 seconds) since we're working with live traffic and want the results to be usable as soon as possible.

Thanks!

David

SampleRoadsAndTrafficJams.ppkx

DanLee

Hi David,

Thanks for the update.

My suggestion on creating a new fc and appending the original features into the new fc was to get the data in a standard stage, so the XY Resolution and XY Tolerance for your data would be as shown below. I didn't think this would resolve the Align Features problem, but it would ensure data integrity for analysis down the road.

As I mentioned before, the tool is NOT designed for matching/aligning two sets of shifted network like features. I am not sure it would work well even if you have common fields as the Match Fields between them. If you could share some more data, I can help assess how the problem might be solved.

DavidSchuster

Dan,

Sorry for the delayed reply. I tried your suggestion of creating a new feature class and appending but unfortunately that did not work. However, I did find what I think might be the cause for the different alignment behavior between the two target road feature classes. Although the geometries of the two target road feature classes was the same, the order of the features within the feature class was not. I think the Align Features tool is somehow affected by the order that the features appear in the feature class. When I took the problematic target roads, and exported them into the same order as the working feature class, the align tool behaved as expected.

Unfortunately, I'm not sure there's much I will be able to do about this, except for somehow using the Match Fields parameter on the Align Features tool - I just have to figure out how to create an ID that can be shared between both the input features and the target features.

Thanks again for your help!

DanLee

I understand. Would you be willing to share more complete data so I can see the real situations?

By the way, I noticed that your TrafficJamLine_Original has the standard xy resolution which is 1/10 of the xy tolernce, but TargetRoads1 has non-standard xy resolution and xy tolerance. I am not sure if it would make a difference in what you are trying to do, but it may potentially cause invisible problems or bad result in your workflow.

You can try the following:

- Use Create Feature Class to create a new empty feature class using TargetRoads1 as the Template Dataset and TrafficJamLine_Original for the Coordinate System.

- Use Append to add all features from TargetRoads1 to the new feature class.

DavidSchuster

Although 3ft search distance works, you'll see the problem again if you try a search distance of 5ft. And unfortunately in my case I can't make the search distance too small because the traffic jams lines are coming from a completely different provider. Some of the jams are off by as many as 10 feet, sometimes more.

DanLee

I tested Align Features; it worked for me without setting spatial index grid size.

DavidSchuster

Thanks for the reply Dan!

I've attached a sample project and some images showing the issue. For simplicity, I eliminated all the roads and traffic jams except for the ones I'm testing the problem with.

The black lines represent a straight section of a service road, and a turnaround section that forks off of the service road. These are the target geometries I'm trying to align a traffic jam to. There are two versions of this target roads feature class. The geometry in both is identical - the only difference between the two feature classes that I can find seems to be the spatial index grid size. "TargetRoads1" has a grid size of 760ft. "TargetRoads2" has a grid size of 980ft. The input lines feature class has a grid size of 2600ft.

The red line represents the traffic jam that we are trying to align to the target roads. Visually, you can see that the jam should line up with the straight section of the service road. When aligning against "TargetRoads2", the Align Features tool gets it right (green line). But when aligning against "TargetRoads1" it gets it wrong (orange line) - the jam aligns briefly to a section of the turnaround, and then jumps back to the straight section of the service road. (p.s. I used an align distance of 20 ft for all of my tests)

I've tried removing and recreating the spatial indexes on the feature classes using various grid sizes to see if I can improve the results and make them more consistent, but I don't have a good enough understanding of what they mean. I'm hoping someone might be able to shed some light on it.

Ignoring that these are road segments, it seems like the Align Features tool should be able to handle a use case like this, shouldn't it?

Thanks for your help!

David

TestingAlignFeatures.ppkx

TargetRoads (black lines - service road and turnaround).png

Original Traffic Jam Line (red line).png

Test1 - Incorrect alignment (orange line) - target road spatial index grid size = 760.png

Test2 - Correct alignment (green line) - target road spatial index grid size = 980.png

DanLee

Align Features tool is not designed to align two sets of network features but to align adjacent features. It would be helpful if you could show a screenshot of a typical area or share a sample data. I wonder what you need might be spatial adjustment, such as rubbersheeting.

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