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www.undertowsoftware.com • View topic - Details about dataset
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Details about dataset

PostPosted: Thu Apr 11, 2013 8:28 am
by jimwelch
I was asked these questions by one of my clients, but didn't know how to answer them. I also thoroughly checked the documentation that came with mappro80, but didn't find this information anywhere. I was wondering if anyone here could help.

What datum is the tele atlas dataset (used in mappro80) based on?
What projection is it in?
What is the accuracy of the data?

Thanks in advance to anyone who can shed some light.

Re: Details about dataset

PostPosted: Thu Apr 11, 2013 9:22 am
by Gyrotech
You may have just opened Pandora's box :-) I'mm try to answer your questions, but remember, this is a lot more complex than what you think :-)
jimwelch wrote:What datum is the tele atlas dataset (used in mappro80) based on?

* WGS84

jimwelch wrote:What projection is it in?

* Geographic (not projected)
BTW, these details are in the MultiNet Shapefile 4.3.2.1 Format Specifications, http://read.pudn.com/downloads119/ebook/508039/MultiNet_Shapefile_4-3-2-1_Version_Final_v1-0.pdf)

jimwelch wrote:What is the accuracy of the data?

An this is where "it depends" :-) You actually should look at these links (there are many others) and make up your own mind.

http://www.spatialinsights.com/catalog/product.aspx?product=95 (Between 5 and 12 meter accuracy, usually better)

http://www.mapmart.com/TeleAtlas/PopUps/TeleAtlas_Info.htm (12 meters or better for 80% of the US)

http://www.gpsmagazine.com/2006/07/navteq_vs_teleatlas_which_one.php#.UWavy6Lqlg0 (Navteq is better, 2006)

https://njgin.state.nj.us/oit/gis/NJ_NJGINExplorer/docs/Roads_Feasibility_Presentation.pdf (NJ TeleAtlas comparison)

http://www.mail-archive.com/google-maps-api@googlegroups.com/msg39725.html (TeleAtlas 400m off)

http://www.prnewswire.com/news-releases-test/tele-atlas-announces-industry-benchmark-for-digital-map-accuracy-51589467.html (Teleatlas, Industry Benchmark)

Does this info answer your questions? If you are able to get more definitive answers regarding the accuracy of the data, please post it here. Many of us would love to know. Undertow should probably make this type of info readily available in the documentation of their SDK.

Re: Details about dataset

PostPosted: Sat Apr 13, 2013 1:41 pm
by jimwelch
Thank you very much for the info.

For some reason I thought that the accuracy was much better than that. Are you sure? The map data on most GPS devices I have used, appear to be within a small fraction of a meter and most of them are right on. I wonder why/how their data is so accurate and the Teleatlas data isn't!

Re: Details about dataset

PostPosted: Thu Jun 20, 2013 12:21 pm
by Luke.Leone
Jim, how did you determine that your GPS data is more accurate? Did you get that from detailed specs of the GPS manufacturer? I'm trying to get similar info for my Garmin, but having a hard time getting such details :-:

Re: Details about dataset

PostPosted: Thu Jun 20, 2013 3:40 pm
by artmart
Hey Luke, I know nothing about MapPro, but know a little something about a GPS unit and researching their info. What Garmin model to you have? I don't recall the specs for my unit but I do recall that my model had an accuracy rating and some of it had to do with the number of satellites you were tracking. I recall reading these specifications for several brands and models and having my unit it reminds me how accurate depending on the number of satellites.

I used my Garmin GPS60cx (without loading the topo map overlays) on a Yosemite backpack and it seemed like it was VERY accurate (maybe 15 ft resolution or less) but it was close enough that I did not worry about the accuracy. I was with a more experienced backpacker and when he kept insisting where we left our packs. We had dropped them to try and get our bearings for a snow covered trail and needed to travel lighter to do so. I then used it find them since his paper tracking was about a 1/2 mile off and while it took me a while to convince him that my GPS had the exact location that I had saveed, he didn't wanna believe the GPS since he was an old map and compass guy and his first GPS unit he ever bought was NOT very good and didn't believe mine was either. He finally caved and I was very relieved when we found them with a near direct route! He mostly grumbled about "luck" and "I knew where it was all the time" and it actually helped me a second time on this same trip (no grumbling this time) but I don't remember the details. Now with the topo overlays, I am very impressed with accuracy.

If you provide your GPS model, maybe I can help you find what you're looking for.

Re: Details about dataset

PostPosted: Thu Jun 20, 2013 11:07 pm
by Luke.Leone
Thanks, Art, but that's not what we are talking about. I know what the garmin resolution is in terms of the Lat/Lon coordinates that are calculated based on the GPS birds and how that depends on the # of birds the device is locked on, how the coordinates are calculated, etc. What we are talking about is the resolution of the dataset that is supplied with the garmin (or whatever other) device. Those are two totally different things. That's why I asked Jim, "how did you determine that your GPS data is more accurate". And, so that we don't waste time going back and forth :-), just because the GPS gets a fix, gets a Lat/Lon and that displays a mark "right on the street", that doesn't mean that the resolution of the underlying street data and the accuracy of the Lat/Lon GPS signal are the same. GPS devices use what is called snapping, which looks at the Lat/Lon acquired, looks at what is the "closest" street section and then "snaps" the point onto the street, even if it does not agree 100% with the signal.

Re: Details about dataset

PostPosted: Fri Jun 21, 2013 2:11 am
by artmart
Ah yes, I know what you are talking about now... thanks for the explanation. Duh.

Re: Details about dataset

PostPosted: Fri Jun 21, 2013 10:25 am
by UShadow
Luke.Leone wrote:which looks at the Lat/Lon acquired, looks at what is the "closest" street section and then "snaps" the point onto the street, even if it does not agree 100% with the signal.

Your explanation was very good! I just put a graphic together for anyone who is still confused. Hope it helps!
road_gps.png
road_gps.png (46.69 KiB) Viewed 8310 times

Re: Details about dataset

PostPosted: Sun Jun 23, 2013 3:43 pm
by mAlagi
Well, the way you explained it makes absolute sense! Thanks ushadow.