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#1
razornole

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Hello,

I'm trying to insert point (or line) features on a pre-existing trail map in ArcMAP 9.2. I'm measuring trail degredation and I want to insert in GIS where the degraded sections of the trails are. I measured the degraded sections of trails in the field with a measuring wheel, all distances from the trail head.
What I would like to do is start from the trail head and create a feature 50 meters (or any distance) down the trail. All I can seem to find in the help dialog uses Cartesian coordinates or way points. I don't have that kind of data. I would like to think that there would be a quick way to do this.

Thanks,
kru
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#2
peanut

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You could dissolve the line for your trail into one feature and from here use the split tool from the editor toolbar to split your line the way you want. The divide tool might work as well but I don't have much experience with it.

Hope this helps.

Rich

#3
razornole

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You could dissolve the line for your trail into one feature and from here use the split tool from the editor toolbar to split your line the way you want. The divide tool might work as well but I don't have much experience with it.

Hope this helps.

Rich



Thanks I'll give that a shot when I get back to campus tomorrow.

kru
"Ah, to see the world with the eyes of the gods is geography--to know cities and tribes, mountains and rivers, earth and sea, this is our gift."
Strabo 22AD

#4
A. Fenix

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hello kru,

as a caveat to what rich said, you can also calculate the feet/miles/etc of the trail arc to match your field measurements, depending on how many vertices the arc has (check out example i attached). this will give you a pretty good idea right off the bat of where your degraded sections will be, and from there you can decide whether dividing the line or creating a degraded point data layer will work best for your situation. :)

~a~

Attached Files


Analisa Fenix
GIS Manager/Chief Cartographer
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#5
tellett

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Hi Kru, I would go for the splitting option as well. Make sure the trail is one object and then you can start splitting it at any distance. You can only split any 'line' in 2 pieces so you'll have to split it quite a few times but I guess thats the easiest way to do it. You can read about splitting in the help guide but its pretty easy, just select the line with the editing arrow and then select split from the editing drop down list then choose split by distance, then for the distance put in the first measurement you have after the trail head start. If you want an even easier option thats not so accurate you can always use the ruler and then digitise a new layer. I'd go for the splitting option though.

#6
Polaris

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Kru -

It is pretty unlikely that your wheel measurements will match the length of the GIS line segments. Wheel distances are generally longer since the mapping will not capture every small bend in the trail. The further you go from the trailhead, the greater the difference will be.

One approach I've used to deal with this is to define the length of your trail as the length measured with the wheel, then divide up the trail into small equal length segments corresponding to wheel measurements. This won't be perfectly accurate, but can get you closer.

Ideally, you would have GPS points at the start and end of each degraded segment.

Analisa may have already alluded to this issue but I'm not sure.

Eric

#7
razornole

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Kru -

It is pretty unlikely that your wheel measurements will match the length of the GIS line segments. Wheel distances are generally longer since the mapping will not capture every small bend in the trail. The further you go from the trailhead, the greater the difference will be.

One approach I've used to deal with this is to define the length of your trail as the length measured with the wheel, then divide up the trail into small equal length segments corresponding to wheel measurements. This won't be perfectly accurate, but can get you closer.

Ideally, you would have GPS points at the start and end of each degraded segment.

Analisa may have already alluded to this issue but I'm not sure.

Eric


Thank you everyone for the responses. I will definitely try the splitting method (though I realize some of my data may be point data). I'm not trying to "map" these degraded sections, but rather get the degraded and non degraded sections of the trails on their own layer in order to see how they lay spatially with my geology, hydrology, precipitation, and ecology layers. Then I can do spatial analysis to see if there is any statistical correlation between these and trail degradation.

Eric you are right, there is a discrepancy on trail length with my GIS and field measurements. On average each trail segment is about 700 meters shorter on the GIS layer for an error margin of <10%. How do I use your method and define the length of the trail to my field measurements? This would be perfect as I was wondering how I was going to define my degraded sections near the terminus of the trail when that length isn't on my GIS layer. Unfortunately I don't have the GPS waypoints as the Glaciated mountains and temperate rain forests of Olympic National Park were not conducive to my hand-held GPS.

Thanks again,

kru
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Strabo 22AD

#8
paul

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Since you are using ArcMap 9.2, you can use the Linear Referencing geoprocessing toolset to do all this. Basically you would convert your trail polyline to a route, and then create route events using an Excel table containing the measured distances for the degradation.

I create race course maps, and have to deal with deviations between measuring wheels and digitized GIS data all the time. One good way to "normalize" the GIS data to the measuring wheel is once again to use Linear Referencing. Look at the Calibrate Routes tool. In a nutshell, you can "force" the linear distance of your polyline to equal the distance measured by your wheel. If you had GPS waypoints, you could calibrate to those, which would "anchor" the linear referencing to those points. But even when you don't have control points, doing a simple calibration will get things pretty close. It's not perfect, but will correct the vast majority of your data within reasonable limits.

See link below for documentation. Once you get the hang of it, Linear Referencing in ArcGIS is a really handy tool.

http://webhelp.esri....ear_referencing

#9
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Since you are using ArcMap 9.2, you can use the Linear Referencing geoprocessing toolset to do all this. Basically you would convert your trail polyline to a route, and then create route events using an Excel table containing the measured distances for the degradation.

I create race course maps, and have to deal with deviations between measuring wheels and digitized GIS data all the time. One good way to "normalize" the GIS data to the measuring wheel is once again to use Linear Referencing. Look at the Calibrate Routes tool. In a nutshell, you can "force" the linear distance of your polyline to equal the distance measured by your wheel. If you had GPS waypoints, you could calibrate to those, which would "anchor" the linear referencing to those points. But even when you don't have control points, doing a simple calibration will get things pretty close. It's not perfect, but will correct the vast majority of your data within reasonable limits.

See link below for documentation. Once you get the hang of it, Linear Referencing in ArcGIS is a really handy tool.

http://webhelp.esri....ear_referencing



Thanks to all who helped and Paul. After 2 weeks I finally figured out the some/most of the Linear Referencing Toolset. I was able to generate an event table with all my degraded sections, and they all were referenced perfectly on my calibrated routes.

Now I need to reference control points (point features) every 20 meters along each trail/route. I could/can do this using an event table, but I would have well over 6,000 point feature. Just wanted to see if there was an easier/quicker way of doing this, maybe SQL or something similar.

kru
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Strabo 22AD

#10
paul

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Now I need to reference control points (point features) every 20 meters along each trail/route. I could/can do this using an event table, but I would have well over 6,000 point feature. Just wanted to see if there was an easier/quicker way of doing this, maybe SQL or something similar.

kru


Alas, the SQL ability of ArcGIS is quite weak. As far as I know, you are limited to just Select * Where commands. You would probably have better luck using Manifold in that regard. I think if you are using ArcGIS, you are stuck with generating points from tables (unless I am missing something).

#11
razornole

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Now I need to reference control points (point features) every 20 meters along each trail/route. I could/can do this using an event table, but I would have well over 6,000 point feature. Just wanted to see if there was an easier/quicker way of doing this, maybe SQL or something similar.

kru


Alas, the SQL ability of ArcGIS is quite weak. As far as I know, you are limited to just Select * Where commands. You would probably have better luck using Manifold in that regard. I think if you are using ArcGIS, you are stuck with generating points from tables (unless I am missing something).


Ok that is good to know. I finally figured out how to paste 6,000 rows in a GIS table at one time, and I was able to generate those point events relatively quickly.

Thanks again to all for your help,
kru
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Strabo 22AD

#12
paul

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Glad it worked for you. Also, if you are using v.9.2, you can directly add Excel tables (.xls) to ArcMap, and generate route events from that. Probably the easiest way to go, opposed to .dbf or gdb tables.




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