Interpolate Route Event Z Values from Route

09-15-2017 07:11 AM
New Contributor

I am trying to interpolate z values based on the example provided in this  post on geonet. In it she has a set of know x,y,z locations that she turns into a Polyline Z and converts to a route (PolylineZM). Then she places (using Locate Features Along Routes) other points of interest with unknown z values on the route and uses Calculate Geometry in the attribute table to get the z values at those points. I would like to do the same, but am having issues because my 2D/x,y points won't locate themselves on my 3D/x,y,z route, or, if they are, they are refusing to calculate geometry relating to z values.

I created the route from points I had and tried to locate my route events on the route. I tried yet again after my initial post and they all showed up as route events, but they won't calculate the z geometry for my points of interest. My points are just Point M, while the geonet poster's points were PointZM. As a result, Z values aren't even an option in the Calculate Geometry menu. The only time I've been able to Calculate Geometry with z values was when I put some z values (from the route) into my route events before locating them on the route, but only those edited records would calculate geometry. I need to interpolate the unknown route event z values from the route, and it was somehow done in the above geonet post, so I'm hoping it really is possible.

Is there a way to make all of these route events into Point ZM without explicitly setting z values before locating them on the route?

I tested by putting some z values (from the known route z values) in the some of the rows of the route event table.
The points I assigned test/known z values to and would generate values when I used Calculated Geometry but only they would, and I was trying to get z values for all my points.

I tried adding NULL values to the z field in hopes of making clear it should be 3D and has unknown z values rather than a z value of 0, but the z values get removed when I run the Locate Events Along Route tool if there are only NULL z values, leaving me with just a PolylineM that won't interpolate z values from the route. If I try to add the z values back with Feature to 3D by Attribute, it will remove the event layer from the route and leave me with a PolylineZ. It will keep z values if there are some actual (non-zero, non-NULL) values, as when I ran my previously mentioned tests, but that still leaves me with a bad PolylineZM since, as previously mentioned, my points of interest don't have z values and so are omitted/can't have their z values interpolated from the route.

Leslie Harwood

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3 Replies
Esri Community Manager

Hi Erin-


Thanks for asking your questions and welcome to the GeoNet community! I wanted to let you know that we're moving your question to the space so our Esri and user subject matter experts can further help answer this and future questions.  So you're aware on how and where to post your questions, here's a few quick tips and reminders:

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Thanks again for contributing and I hope this helps and let us know if you have any questions.


Michelle Mathias
Manager, Community Experience & Programs
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MVP Esteemed Contributor

Did the Add-in not work that Richard referenced?

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New Contributor

No, I haven't tried it because I didn't think the Add-in was needed to accomplish the task based on the solution provided by the original poster. She explained her process and, though she thanked him for pointing her towards linear referencing, never mentioned using or even testing Richard's Add-in. It seemed to me she was only using the innate capabilities of the Linear Referencing tools. Am I mistaken?

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