topic Distance Between Trail Marker Issues? in Geoprocessing Questions

Distance Between Trail Marker Issues?

DylanPhilyaw — Wed, 08 Jun 2011 19:28:45 GMT

I hope someone can help with this.

I am interning for Grandfather Mountain State Park. All of the park trails have been GPSed as polylines. We just put up new trail markers along all of the trails and GPSed those as point data. I am trying to find some way to measure the distance each trail marker is from the trail head. They are using this data for 911 database purposes. I am using ArcGIS 10. Does anyone have any suggestions on how to do this without manually doing it with the measure tool? Any help would be great!

Dylan

Re: Distance Between Trail Marker Issues?

DarrenWiens2 — Wed, 08 Jun 2011 20:21:40 GMT

You can either use Near or Generate Near Table, both of which require ArcInfo level licensing. If you don't have ArcInfo, it will be a little more difficult.

Re: Distance Between Trail Marker Issues?

HardolphWasteneys — Wed, 08 Jun 2011 20:48:07 GMT

Dylan,

this is a Linear Referencing Toolsapplication involving the "Locate Features Along Routes" tool.

First you need to set up your polyline FC with a field that identifies the individual trails consistently then run the Create Routes tool on them with the trail name field as the Route Identifier Field, Measure Source as Length and Coordinate Priority as the position of the trail head relative to the trails.

This creates a new feature class that is aware of its length, or "M" value, at any point.

Now you intersect that with the signpost GPS points using the Locate Features Along Routes tool.

Again you will need to have an identifier field in your GPS point FC that shows the trail name with exactly the same syntax as in the Route Identifier field in your route FC.

One caution when using the tool: you may have to play with the "search radius" unless your signpost points are "snapped" to the polyline that form the routes. Or you could also set the precision of your FCs to a value like 5 m. This is because your GPS precision will not show the points as intersecting the polylines if you use the default 0.0001 m precision even if they were taken with a top of the line RTK unit rather than a Garmin Map 60 CSx or whatever.

Also make sure nothing in the point or route file is left selected or you will get only a partial output.

Open the Output Event Table and look under the "MEAS" field for the distances of the GPS points along the trails. The output Event Table can be exported as a new FC that records the trail sign distances.

Good luck,

Re: Distance Between Trail Marker Issues?

ThomKaye — Wed, 08 Jun 2011 21:57:41 GMT

Dylan-
Somewhat off-topic but I am doing something similar in regards to conducting a trail survey to support accurate distances. I am limited to using commercial GPS units to survey my trails therefore perhaps compromising the accuracy of my collection. I am trying to collect true centerline data to maintain as much integrity in my resulting distance calculation. Therefore I exploit satellite orbits, survey in the winter (leaves off), set collection parameters to a small time interval and some post processing. Are these some of the steps you've taken? Are their any I missed?

Thom

I hope someone can help with this.

I am interning for Grandfather Mountain State Park. All of the park trails have been GPSed as polylines. We just put up new trail markers along all of the trails and GPSed those as point data. I am trying to find some way to measure the distance each trail marker is from the trail head. They are using this data for 911 database purposes. I am using ArcGIS 10. Does anyone have any suggestions on how to do this without manually doing it with the measure tool? Any help would be great!

Dylan

Re: Distance Between Trail Marker Issues?

DylanPhilyaw — Thu, 09 Jun 2011 11:29:43 GMT

That sounds like pretty much what I did except, I have had to take my points during the summer with leaves on. What commercial GPS are you using? If it is a newer Garmin there is a setting that allows you to use the Wide Area Augmentation System (WAAS). This can provide more accurate results. I also believe that other commercial GPS units have this feature available also. Another thing that I did was use the "average function" when taking waypoints. That helped me get my estimated accuracy down below 3 meters.

I hope that this helped, if not just shoot another post and I will see if I did something similar.

Dylan

Re: Distance Between Trail Marker Issues?

DylanPhilyaw — Thu, 09 Jun 2011 11:32:37 GMT

Thanks Hardolph,

I have to do fieldwork first thing this morning but I will be in the office this afternoon and let you know how this works out. I do know that I was trying something similar yesterday but had no direction on how to do it. Thank you for the detailed answer that sounds like it should work.

Dylan

Dylan,

this is a   Linear Referencing Toolsapplication involving the   "Locate Features Along Routes" tool.

First you need to set up your polyline FC with a field that identifies the individual trails consistently then run the   Create Routes tool on them with the trail name field as the   Route Identifier Field, Measure Source as Length and Coordinate Priority as the position of the trail head relative to the trails.

This creates a new feature class that is aware of its length, or "M" value, at any point.

Now you intersect that with the signpost GPS points using the   Locate Features Along Routes tool.

Again you will need to have an identifier field in your GPS point FC that shows the trail name with exactly the same syntax as in the Route Identifier field in your route FC.

One caution when using the tool: you may have to play with the "search radius" unless your signpost points are "snapped" to the polyline that form the routes. Or you could also set the precision of your FCs to a value like 5 m. This is because your GPS precision will not show the points as intersecting the polylines if you use the default 0.0001 m precision even if they were taken with a top of the line RTK unit rather than a Garmin Map 60 CSx or whatever.

Also make sure nothing in the point or route file is left selected or you will get only a partial output.

Open the   Output Event Table and look under the "MEAS" field for the distances of the GPS points along the trails. The output Event Table can be exported as a new FC that records the trail sign distances.

Good luck,

Re: Distance Between Trail Marker Issues?

DylanPhilyaw — Thu, 09 Jun 2011 13:41:18 GMT

Thanks

That worked perfectly

Dylan

Re: Distance Between Trail Marker Issues?

ThomKaye — Thu, 09 Jun 2011 17:55:32 GMT

Thanks for the input Dylan. I took the steps you outlined as well during my surveys. Hopefully it will yield the best possible results.

One software program that I use to assist with the visibility of the satellites is Trimble's Planning software. It essentially helps with surveying during a given time span by telling you how many satellites will be visible. http://www.trimble.com/planningsoftware_ts.asp

i've attached a screen shot.

I can't seem to find a post-processing application for commercial units, although I am sure one exists. For professional units you can correlate your results to CORS stations to get the best possible accuracy using proprietary applications. I'll reach out to the ESRI mobile team to see if they have any ideas.

That sounds like pretty much what I did except, I have had to take my points during the summer with leaves on. What commercial GPS are you using? If it is a newer Garmin there is a setting that allows you to use the Wide Area Augmentation System (WAAS). This can provide more accurate results. I also believe that other commercial GPS units have this feature available also. Another thing that I did was use the "average function" when taking waypoints. That helped me get my estimated accuracy down below 3 meters.

I hope that this helped, if not just shoot another post and I will see if I did something similar.

Dylan