# Use of linear referencing on a route that span over 3 different UTM zones

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10-22-2018 12:52 PM
New Contributor II

I have a long route (~2400 KM) that span 3 different UTM zones. (N - 37, 38, 39)

On this route there is a sign every 1 km-approximately (km marker), these signs help in determining the exact location of assets along the road etc…

I have the actual location of these signs as a point and it turned out that the distance between 2 markers is between 1100 m to 1200 m in general so there is an error in these markers location caused by human mistakes. So I need to create new km markers that conserve the distance between the 2 markers (1000 m) using linear referencing and event tables on my road route.

But the problem is my route passes by 3 different UTM zones and all of my data are geographic WGS84 which is in degree, therefore, I can’t create km markers using linear referencing and event table in this case for each 1 km as my m measurements if the route was WGS 84.

And I need the rout to be 1 single record along the 3 UTM zones so I can’t divide the route based on the projection boundary. Even though I tried to do this and also had an error equal to 20 m on the boundaries of the projection zone.

What should my route projection be in this case? So that the linear referencing and event tables work without any distortion.

For sure the route should be in a projected coordinate system since we're using meters (1000 m) to dived the route or you think we can use the geographic coordinate system by transforming the m value to a decimal degree.

3 Replies
MVP

What is your desired/allowable level of accuracy?  Three UTM zones covers about 1/3 of the USA, and does introduce a lot of distortion.  So how much distortion is too much for you?

I just posted this idea (with LRS in mind specifically) for the exact reason/problem you are having.  GIS Design Support for NSRS 2022 and Low Distortion Projection Zones

If you have only one route, you could potentially find or define a projection that would satisfactorily minimize distortion for that route.  Probably your best option is to segment the route shapes between projections at a state level, build a bunch of LRS routes and calibration points then use those to calibrate the whole route with attributes as opposed to shape length definition, but then again, what is your desired/allowable level of accuracy?

Upvote my idea and maybe someday you could use GIS and LRS for something like this with Surveying level accuracy, distortion a couple 10's of parts per billion.  You can't eliminate distortion but you are asking the right question to minimize distortion for sure.

MVP

One more thought, if the route happens to be a railroad, and if you happen to have some inertial measured data, you could potentially use the inertial at-ground distance measurement as the length of the route, to accurately build your LRS Route.

New Contributor II

thank you very much Kyle. it is a railroad and we did have physical point along the route that we know its location. so basically we used these point to calibrate the route measurement by setting a (from to) for the  m value.