Welcome, Guest. Please login or register.

Login with username, password and session length
Forums Search:  


Author Topic: Mapping data source of gpsfiledepot  (Read 4197 times)

happynomad79

  • Jr. Member
  • **
  • Posts: 4
  • Karma: 0
    • View Profile
Mapping data source of gpsfiledepot
« on: December 07, 2016, 05:32:17 PM »
Hi,

i am a newbie to GPS technology.
i am curious about the different between proprietary map (paid map on sale in Garmin website for example) and free maps (which can be dl from mapping interests groups like gpsfiledepot and openstreetmap).

Understand that proprietary map receives their mapping data from from national mapping agencies like U.S. Geological Survey and Ordnance Survey. Where does open source / free maps receive their mapping data from?
Thank you.

Boyd

  • Expert Advisor
  • *****
  • Posts: 4037
  • Karma: 50
    • View Profile
Re: Mapping data source of gpsfiledepot
« Reply #1 on: December 08, 2016, 03:50:10 AM »
GPSFileDepot is a repository of maps made by many different people. It is impossible to make any generalizations about data sources because these people have different methods, goals and experience levels.

Some people follow the mapmaking tutorials on the site, you can skim through these and see the data sources that are used: https://www.gpsfiledepot.com/tutorials/how-to-create-garmin-topo-maps---part-1---setup/

But I think you may have it backwards when you say "Understand that proprietary map receives their mapping data from from national mapping agencies like U.S. Geological Survey". Here in the US, data from public agencies such as the USGS is free for anyone to download and is a primary source for people (such as myself) that contibute free maps to this site.

Commercial products may incorporate some of this data but are more likely to use private data sources which are often more up to date and comprehensive, such as HERE (formerly NavTeq) or Digital Globe. Google and Apple have made substantial investments in gathering their own proprietary data also.

happynomad79

  • Jr. Member
  • **
  • Posts: 4
  • Karma: 0
    • View Profile
Re: Mapping data source of gpsfiledepot
« Reply #2 on: December 08, 2016, 06:28:48 PM »
Dear Boyd,

Thanks so much for enlightening me.

Can i just ask you one more question which has puzzled me despite surfing around for info.

Understand that routing and way-points are usually stored in non-non proprietary file format (like GPX) which can be easily converted into other format using software like gpsbabel so that anyone can create and share their routes in various platforms (be it dedicated GPS units or phone based apps). I guess i am wrong again this time round :-[

How about maps? Can proprietary maps be easily converted from img to imi etc?

Thank you!!

jolly47roger

  • Mapper
  • ***
  • Posts: 95
  • Karma: 8
    • View Profile
Re: Mapping data source of gpsfiledepot
« Reply #3 on: December 09, 2016, 03:55:36 AM »
There are some tools that will convert maps but, because different map systems implement features in different ways, it is unlikely that you will be able to get an exact copy.

However, many of the maps posted on this site have licence conditions that prohibit conversion, re-engineering etc. - so check carefully!

Boyd

  • Expert Advisor
  • *****
  • Posts: 4037
  • Karma: 50
    • View Profile
Re: Mapping data source of gpsfiledepot
« Reply #4 on: December 09, 2016, 05:08:58 AM »
Garmin's traditional map format is vector-based and consists of lines, points and polygons. These are stored in a proprietary database along with instructions for how to connect line segments to create a road or polygon vertexes to define a lake for example. Garmin has never formally published their format and considers it proprietary. So all the maps here have been created with third party tools that have reverse-engineered Garmin's format. This is actually a violation of Garmin's software license, but since it helps them sell GPS units, they choose to "look the other way" and allow it.

It may be possible to convert some Garmin maps to other formats, but it is much better to use the source data to create a different map. And as jolly47roger pointed out, "free" is not necessarily the same thing as "open source".

There is another category of maps that are based on raster images. Basically, these are just pictures that contain additional information that aligns them with the surface of the earth. Newer Garmin handhelds support raster imagery in the form of "custom maps" in Google's .kmz format. You will find a number of these at GPSFileDepot as well. Since it's just a picture, it could be anything, such as a scanned paper map or aerial photo. These can be converted to other formats fairly easily.

.gpx files contain only points and lines. Waypoints and Tracks can usually be converted to many different formats using a tool like GPSBabel as you said. Routes are a little more complicated, since they rely on having a routable map. Routable maps contain additional information about how the roads are connected and allow the caluclation of efficient routes between points. There are hardly any routable maps here at GPSFileDepot (they are much harder to make), so having a route in a .gpx file won't be of much use. A Garmin gps will give you an error to the effect of "no routable roads were found" if you try to use a route with them.
« Last Edit: December 09, 2016, 05:11:49 AM by Boyd »

happynomad79

  • Jr. Member
  • **
  • Posts: 4
  • Karma: 0
    • View Profile
Re: Mapping data source of gpsfiledepot
« Reply #5 on: December 09, 2016, 06:06:48 AM »
Thanks jolly47roger and Boyd for your explanation.

Have nice weekend.