Garmin Topo (and base map) accuracy

[wheagy]

If this has been discussed before, please point me to it (didn't find anything in a search).

 

I have a new 60csx (did the latest firmware updates). I only have the base maps and

24k topo maps installed. I've noticed that when driving or biking, my position frequently

appears to be off to the side of a road or trail by up to 40 feet. This is more pronounced

when traveling east-west or west-east, where I usually am to the north of the road.

On north-south roads, I appear on the road, although my position may be off...hard

to tell. I have heard that roads in the topo are not all that accurate, but I see the same

behavior on base maps. I've used other GPS units (auto and aviation) and have not

noticed this before (it's much harder to tell with aviation GPS units). In my auto unit, it

appears the display algorithm will "snap" my position to the nearest road even if my coords

don't say I'm exactly on a road. I realize the 60csx is more general purpose, so maybe

it doesn't do this? But, is is common for a basemap road to be that far off? If my GPRs

is indicating 20 feet accuracy, should I expect to see myself off to the side of a road?

It seems that the basemaps my have some inaccuracy since when driving I'll notice a

long gradual curve on the road, but this is not reflected on the base map. It may just

show up as a straight segment. I'm not used to this since my auto GPSr has pretty

realistic depiction of the same road...including gradual curves. Does City Navigator

have better road data?

 

Thanks,

 

Win

[CenTexDodger]

If this has been discussed before, please point me to it (didn't find anything in a search).

 

I have a new 60csx (did the latest firmware updates). I only have the base maps and

24k topo maps installed. I've noticed that when driving or biking, my position frequently

appears to be off to the side of a road or trail by up to 40 feet. This is more pronounced

when traveling east-west or west-east, where I usually am to the north of the road.

On north-south roads, I appear on the road, although my position may be off...hard

to tell. I have heard that roads in the topo are not all that accurate, but I see the same

behavior on base maps. I've used other GPS units (auto and aviation) and have not

noticed this before (it's much harder to tell with aviation GPS units). In my auto unit, it

appears the display algorithm will "snap" my position to the nearest road even if my coords

don't say I'm exactly on a road. I realize the 60csx is more general purpose, so maybe

it doesn't do this? But, is is common for a basemap road to be that far off? If my GPRs

is indicating 20 feet accuracy, should I expect to see myself off to the side of a road?

It seems that the basemaps my have some inaccuracy since when driving I'll notice a

long gradual curve on the road, but this is not reflected on the base map. It may just

show up as a straight segment. I'm not used to this since my auto GPSr has pretty

realistic depiction of the same road...including gradual curves. Does City Navigator

have better road data?

 

Thanks,

 

Win

 

You did not say what road navigator you have. It doesn't really matter, but it it were a Garmin, you would be able to tell what kind of detail City Navigator would have as all Garmins use City Nav or City Select for their road data.

 

That being said, yes the basemap is as bad as you describe. City Navigator shows the roads as they truly are, or fairly closely. Also the 60 series has the "lock on Road feature so that the GPS will assume you are on a road if it thinks you are off but very near a road. IIIRC you must have City Nav for this feature to work correctly.

[wheagy]

My other GPS is a MIO 168 (does not use Garmin software).

 

This answers my questions.

 

Thanks,

 

Win

[+YuccaPatrol]

Also, don't expect trails on a topo map to be anywhere near perfectly drawn on the map.

[wheagy]

Yeah...that was another question...trail accuracy. Although I assumed that

if the road accuracy was bad, the trail accuracy would be too.

 

There are a couple of trails near here that appear on topo, but when I actuallly

rode them on my bike, I was surprised by how much detail was missing.

 

Win