Hi all!
What I've been told (safe source) about canvec/geobase data origine and
accuracy...
About 5% of the available datasets (usually populated area) have been produced
digitally and have an accuracy better then 25m.
So, almost every thing you'll find in canvec have been scanned from 50K paper
map. The paper map where produced using 50K aerial photographies and their
accuracies were between 25 and 100m (or worst in some case)!
BUT, over the last years
- All the road network has been acquired using high accuracy GPS (90% better
than 10m).
- Every datasets that had an accuracy worst than 30m have been geometricaly
corrected.
Then, the resulting canvec (Federal) datasets have an accurate road network,
and the rest of the content should have an accuracy between 10 and 30m.
However, if you are standing on the bed of a stream/river with your GPS unit
(and having a good satellite visibility), I would say you're probably more
accurate that the available data!
Anyway, I would propose that everyone uploads their GPS traces even if some
exists for the same way because it might helps to see what geometry is right.
Daniel
Date: Thu, 12 Mar 2009 13:29:10 -0400
From: [email protected]
To: [email protected]
Subject: Re: [Talk-ca] ACQTECH vs. Valdate vs. OSM User imput for CanVec HD
I think he's aware that we can't use Google Earth, nor did he ever say to. He
was just saying that his GPS tracks met up with the actual path when overlayed
on the Google imagery, meaning that his tracks are probably more accurate.
About the waterways - I think many of the waterways (smaller ones) were just
traces of aerial imagery onto the topo maps. Waterways are too much of a pain
to do by GPS on such a large scale so I couldn't see them being too accurate,
unless you get a municipality's watershed layers which I've found to be very
accurate and detailed, but those aren't available to the public or under the CC
so it doesn't matter anyways. For all we know the federal data could have been
aerial-->paper topo-->digitized, meaning it could be very innacurate. I don't
know what the metadata says since I'm at work and can't (shouldn't) access it,
so I don't know if it says in there what the source is. I think a user who
knows the area should be the one who decides what should happen to the waterway
or at least compare the bot loaded data with the aerial imagery that's already
available to decide which is nearest to the actual location.
-Kevin (Kevo)
p.s. sorry for sending twice sam, i always forget to press reply all.
On Thu, Mar 12, 2009 at 1:16 PM, Sam Vekemans <[email protected]>
wrote:
Hi,
Ya we (the OSM community) dont use Google Earth (because the map isn't free,
you cant take a printed map of Google Earth/Google Maps and print it in Books.
.. you can with OpenStreetMap.org
By submitting your original GPX tracks to OSM, you then help build the larger
map of the world, the more original GPS tracks that get added to the area, the
more likely and easier it is to accurately tell what map features are more
accurate.
The map that your making (yes, it is useful) however, the OpenCycleMap
currently available, is also available to download as a garmin map from
Cloudmade
http://downloads.cloudmade.com/north_america/canada#breadcrumbs
& the OpenHikingMap is currently in progress which takes the OSM map features
and tones down the highways so then all the trails stand out more. Also, all
the things relevant to Hiking will also be shown.
http://wiki.openstreetmap.org/wiki/Hiking_Map
Here's that the area of discussion looks like on the cyclemap layer
http://www.openstreetmap.org/?lat=49.58793&lon=-114.5186&zoom=17&layers=00B0FTF
But of course, if your not into contributing to OSM directly, im sure Simon
would be able to help out again, and import the latest version of your .mp map
when it's ready :)
Cheers,
Sam Vekemans
Across Canada Trails
On Thu, Mar 12, 2009 at 9:53 AM, Calgary Trail Maps <[email protected]>
wrote:
The current OSM data is from my maps, which are based on my tracks, other than
the ATV bridge which someone else added. You can see them clearly in Google
Earth. I'm working on cleaning this area up for my next release and I'll clean
it up a bit more.
John
From: [email protected] [mailto:[email protected]] On Behalf Of Sam
Vekemans
Sent: March 12, 2009 10:35 AM
To: [email protected]
Cc: Calgary Area Trail Maps; Talk-CA OpenStreetMap; Jean-Sébastien; Dale Atkin;
Richard Degelder
Subject: Re: ACQTECH vs. Valdate vs. OSM User imput for CanVec HD
Hi Simon,
So for the canvec data, it was recorded back in 1979 when the earth was flat ..
lol :-)
it also says that the technique is "vector data" . ... it also says the
planimeteric accuracy is "19" that would be 'meters' ... so your statement of
'15 meters' off makes the canvec data also 'right' in it's own sence.
If your GPS had a better accuracy, then best guess is all you can do.
And John,
Thanks, would u be able to upload all your GPX tracks to OSM?
If not, i can upload that for you, on your request.
Using JOSM, i just download all the local area GPS Traces, and i only see 1
track (Simon's)
And everyone,
Well, i "think" when it says "GPS" as the source, would be from a 'trimble
differencial unit" (but not sure) .. and so, when canvec says it's a "7 Field
completion" then we could says it's as accurate as any mapper account.
And so, looking at the contour lines on the Cyclemap, it looks pritty good.
Anyway,
I fixed the script so it reads as a "river" thats because it's a "Watercourse,
non isolated" for the "Watercourse, isolated" thats when i list it as a
"stream" and for all the "other" and "unknown" I list it as a "stream" so then
they can be manually upgraded.
So for some of them that are labeled... like "York Creek" it's hard to say what
it is.
I could change it so that "Watercourse, non isolated" is listed as a "stream"
would that be better?
Thanks,
Sam
P.S.
I now need to go over the whole set again and fix up the wiki charts. Hopefully
in the next few days it will be better. ... but of course, im always looking
for errors. anyway i published the rules.txt file and added the 'date-time
stamp' from notepad so you can see how old it is.
http://docs.google.com/Doc?id=d2d8mrd_179gnhs54cw
On Thu, Mar 12, 2009 at 8:29 AM, <[email protected]> wrote:
> Hi, i have an area, which i found interesting.
> The York Creek (river) ish..
Are you perhaps refering to this spot?
http://www.openstreetmap.org/?lat=49.58793&lon=-114.5186&zoom=17&layers=B000FTF
http://www.flickr.com/photos/24244...@n03/2777260804/in/set-72157606820699424/
Where I sat with my doggie, having lunch on a fine afternoon last summer.
Looking at the sources available to me (OSM, OSM-GPX, CatMP and Canvec),
it appears that the Canvec waterway (coded 1470171) is about 15m too far
west.
That said, consumer GPS is not going to be very accurate. Look how the
(only!) GPX track is very noisy here. The only real way is to get multiple
GPS tracks going through the area an visually average/discount them to get
an approximately true location.
One thing that we have on our side when looking at waterways, is that
water is lazy and will take the easy route. So if you look at this area
with a contour layer you might be able to confirm which of the waterways
is in the wrong place.
Cheers,
Simon.
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