Track Position Different on GPS vs MapSource??

[jj]

I have an Oregon 300 and recently walked along some railroad tracks which are on the WI Topo I downloaded from this site.  The track I made looked like I was 30 ft off the railroad tracks when I was walking on them.  Once uploaded into Mapsource my track in this program is right on the rail line.

I don't understand how the track can look different on the same map. ANy ideas

[Boyd]

Sorry for the stupid question, but are you sure that you used the same map in mapsource that you had loaded on the GPS?

[jj]

Boyd

No offense.  I feel like my question is a stupid one.  Yes I loaded the Wisconsin Topo from this site to Mapsource and then from there to the GPS.  Thats the map with the railroad detail.  THe only other maps I have are the base map (which has no railroad track detail) and water maps.

[jj]

If I view the track in Google Earth it matches the map on my GPS which is wrong as it shows I'm way off the railroad track I was on.  But in Mapsource it looks right.

What da?

[jj]

Its more like 50 feet off but what's baffling is the track in Mapsource is dead on.  Same map, same track

[Boyd]

I agree, but that doesn't explain the difference between mapsource and the GPS itself. I wonder if it has to do with your projection settings? You should have a menu for something like "Map Datum" on the GPS. What is that set to? I use WGS 84 for all my own maps. Do we know what was used for the WI Topo? I know that this setting can change the appearance of the map, but wouldn't expect it to affect your position display. But it's all that I can think of.

[maps4gps]

The mapsets should be in WGS84/NAD83 as all the source data uses that and is processed in GM using that datum.

gpsmapedit shows the files to be in WGS84

What specific location in Wisconsin?

Is the Oregon set for WGS84?

Were you viewing the data at the same scale on the Oregon and in MapSource?

The track I made looked like I was 30 ft off the railroad tracks when I was walking on them.

  Ah! your Oregon knows best.
1. that is dangerous.
2. that is illegal - you were trespassing on private property.

...what's baffling is the track in Mapsource is dead on.

Agree.

[maps4gps]

Was there a road parallel and near the tracks?    
The mapset is not routable; if the Oregon is set to 'stay on road', it may display your location/track on a nearby road feature.  Maybe Garmin is trying to address concerns about not showing your location on a road/street when the map data is somewhat inaccurate and/or to compensate for the normal 'error' in GPS location.  The position is recorded correctly, just adjusted on the display; therefore in MapSource it shows your actual location.

[Boyd]

Was there a road parallel and near the tracks?    
The mapset is not routable; if the Oregon is set to 'stay on road', it may display your location/track on a nearby road feature.

Never thought of that, but you're right - road lock can cause this kind of strange behavior. However, on most units, the road lock is applied to the track itself, so I'd expect to still see it in Mapsource. Most of Garmin's new basemaps are routable, so it could very well be snapping to a basemap road which is hidden under the topo map.

[maps4gps]

However, on most units, the road lock is applied to the track itself, so I'd expect to still see it in Mapsource.

I can not say.  I never tried using it and do not have a mapset which is routable.
I would not have expected turning hillside shading off to change the background color from brown to light cream either; especially when the only mapset on the unit with such data was the 'built-in' basemap and it was disabled.  Seems how Garmin links some things is not very obvious nor intuitive.

[jj]

Thanks for all the ideas.

I don't think its trying to snap to a road.  I notice the same issue with roads on the same map (again its the WI Topo from this site).  My position on the Oregon display is always 30-50 ft east of where I actually am on the earth.  Railroad, Road road, etc.  In Mapsource a track looks ok.

It must be a datum setting.  I have not changed it from the default (I was not aware how to change it).  I'll check that to make sure its WGS84 and try again to see if there is any difference.

Ironically my position in WI is Oregon, WI.

[maps4gps]

For 43n & 90W, NADCON, for 27>83, says 0.0078 south and 0.4448 west - 10.075meters (33 feet) close to due west. 
Were you near/under any high voltage powerlines?

[jj]

You said:

For 43n & 90W, NADCON, for 27>83, says 0.0078 south and 0.4448 west - 10.075meters (33 feet) close to due west.

I assume you're saying two datums have a difference of 33 ft.  Not sure about the powerline significance.  I have this difference no matter where I am in this area (railroad track, many roads, etc)

Thanks for thoughts on this!

[jj]

I found the problem and this could be a bug.

I have Garmin on the water maps in my GPS and enabled.  When I disabled the water maps the topo map snapped to where it should be.  My track now is dead on the rail line where it should be.

Makes me wonder how accurate the water maps will be.  But at least this problem was solved.

[maps4gps]

Nice to hear.  Thanks for letting us know.  Enjoy.