Trail100k vs Garmin Topo East trail Locations

[Comet48]

I just downloaded and installed the Trail100k file into Mapsource and when I toggle in Mapsource between the Garmin Topo USA East file and the Trail100 file I notice that the trail junctions are off little.  The junctions from Trail100 are uniformly about .1 miles east of those on Topo East.

On the attachment from Topo East the cross-hair is where the same junction is displayed when the Trail100k file is loaded. 

Am I missing a setting somewhere or is there anyway to bring these into alignment?


Thanks  Tom

[maps4gps]

Is that the east file from Garmin's USA Topo 100k product?

A difference in datum will produce a consistent position shift, however I do not recall anywhere in the 48 States this being over 100'. 

I checked some local trails in the trail100k file with three other sources, and they are 'right on' to a few tens of feet different.  These sources may have used the USGS 100k data for their trail info.
Garmin never says what their, or their data provider, source info is.

Is it easy for you to get to one (or more) of those locations and obtain a good GPSr location to see which mapset is more accurate?

I do not know of any way to shift mapset data in MapSource.

[Comet48]

Thanks for the reply,

It's an older Garmin product called Mapsource United States Topo Copyright 1999-2002.  The box says: "... comparable to the U.S.G.S 1:100,000 scale paper maps".  I can't get to the WV location in the example I provided very soon, but will try to get to some place closer to home in the next couple of days.

In the mean time here's a track recorded in the southern section of Shenadoah National Park with the Topo East and the trail100k maps for the area overlaided.  There are some significant variations between the track and the Mapsource file and there were some satellite coverage issues when the track was recorded, but the differences between the track and the trail100k maps are pretty consistent with the other example (especially on the left side of the example).

Thanks for your help.

[maps4gps]

As in Garmin (or their data providers) only know the source of the data, so only Garmin (may) know what 'comparable to' means.

You are getting this difference in MapSoruce; is it also like this on the GPSr?  The 'field test' was meant to determine which mapset might have a better location; your track answered that.  Does not seem to be a datum issues as NADCON is indicating a shift of less then 100' in EW and also about half that for NS.

If Garmin used the 'trails' in the USGS 100k data set; there would be no need for you to also use the 100k trails mapset.

[Comet48]

Actually I was hoping to use the 100K Trails mapset in combination with the NE USA Topo 24K mapset that I very recently downloaded from this site.  Not many trails show up on that and despite how out of date trails often are on topo maps, they are still sometimes real useful. This whole endeavor came out of ongoing frustration with how difficult it often is to determine the grade/difficulty of terrain using my Garmin 100k maps.

Tonight I Just uploaded some of the 100K trails maps and NE USA Topo 24K into the GPS for a section of WV and the differences seem to be the same on the GPS as I see on Mapsource. On the attached screenshot the red trail from the 100ktrails file should end on the Forest Service road.

It's a great idea to display the trails with the thicker lines and it looks like this combination will still be pretty useful since the differences are consistent and trail locations on topos aren't exact anyway.  I think I need to check things out further in the field.

What section of the country where you referencing to when you mentioned  ...

"I checked some local trails in the trail100k file with three other sources, and they are 'right on' to a few tens of feet different"? 

I'm curious how that area looks on my Mapsoucre files.

Thanks

[maps4gps]

I put it out there because users of Garmin's first few Topo 24k areas in the West were saying they found few trails than in the Topo 100k product or none at all.  Comment on their more recent eastern areas indicate they have included many trails.

Like most of the mapsets we create, the transportation comes from the freely available Census TIGER files which have little reason to include trails if no-one lives along it.  I had prepared and tested adding the USGS 100k trail data to that of the Census; however, there were many duplicates/overlaps so I considered it might be too confusing to do so and way too much time to do the necessary editing featue by feature. 

I was looking at the trails in the foothills west of Denver, CO.  For comparison I used my CO Topo 7 1/2 (Census 2008 - after data for all counties had been spatialy realigned), CO topo from miscjunk (CDOT were their metadata indicated it was obtained from their mainframe database some years earlier, but no actual source give), and Abovethetimber commercial product (version 1, 2007?, probably Census data and therefore before the area had undergone spatial realignment - not all features may have needed realignment). 

When I get the time, I will also check using trail data the Forest Service created from USGS 24k topos and with 3 ft and 1 ft imagery of the area.

[Comet48]

Interesting, I just checked the area west of Denver using the Garmin "US Topo West" disc (from the same set as the East file) with the Trail100k map file and like you originally said, they concur within a few feet.

Maybe I just need to move

[Comet48]

Thanks I wasn't familiar with gpsvisualizer, but I do use TopoFusion to do that when I'm at the computer.  I find the 3D view to be the most informative. The elevation profiles often contain variation that just doesn't seem right.

I think for the use with the GPS and the small display area the best solution for me is going to be having both the 24k and 100k maps loaded and switch between them as needed.

It's too bad Mapsource doesn't have a method to adjust the calibration of the trail100k files for my section of the country, but I think the trails file will still be a useful aid because they show up so well on the small GPS screen.

Thanks for the advise.

[baileyjiam]

"The junctions from Trail100 are uniformly about .1 miles east of those on Topo East."

I have seen the same thing. On trails in VA and NC, Trails100K indicates the trails are subjectively 200 feet east of the actual trail locations. Once I got a feel for the offset they are usable, but Id like them to be more accurate. Ive observed this in the Shenandoah and in Pisgah National Forest, the the offset was the same in both.

[maps4gps]

Id like them to be more accurate.

We all would; and be more detailed/complete/current - but we have to use what is available and hope for the best.