How to use printed maps for GPS Navigation on Android phones

From VOC Wiki
Jump to: navigation, search

This is a guide on how to use printed maps (such as the awesome Baldwin maps) for GPS navigation using Android smartphones. After trying several applications, the best one I found for this is called OruxMaps and it's available for free on Android Market (Google Play).

There are several steps to this guide: scanning the maps, stitching the scanned images, geo-referencing the digital map and converting to the format that is required by the app on the phone.

OruxMaps can also use offline maps created from online sources such as Google Earth, Google Terrain, OpenStreetMaps,...

Scan the map

Most maps are too large to be scanned in one piece, so the map must be folded and scanned section-by-section. The resulting images must be then stitched to obtain the complete digital map.

Stitch the scanned images

In case your map is small enough to be scanned in one piece you can skip this section. Otherwise after scanning the map you end up with several images that must be stitched together. There are several applications that could be used to accomplish this, the one I like is Hugin because it's open source and allows you to manually adjust and fine-tune the stitching process. To stitch scanned images using Hugin follow the excellent tutorial here. After the optimization step you should obtain a mean error less than 1.0, otherwise something went wrong, go back and check the previous steps, especially make sure the control points are ok.

Geo-reference and convert the map image

After stitching you end up with a raster map, usually in JPEG or TIFF format. The digital image needs to be geo-referenced to be used for GPS navigation. The geo-referencing process establishes the relation between the map pixels and the geographic coordinates. The OruxMaps app has an associated application OruxMapsDesktop that can both geo-reference and convert the map image to the required format.

The OruxMapsDesktop application

After starting the OruxMapsDesktop application you should see a window similar to the one on the right. Fill in the fields in this window as follows:

  • Image file : The scanned/stitched image of the map.
  • Calibration file : If some other GIS program is used to geo-reference the map, select the corresponding calibration file here, otherwise leave this one empty and fill in the fields below.
  • Datum and projection : Select the map datum and projection. This information can be found on the edges of most maps. The Baldwin and the NTS maps are using either North American Datum of 1927 (NAD27) or North American Datum of 1983 (NAD83). Projection is usually UTM, zone 10 (for this part of BC).
  • Reference points : You need to enter the image X,Y locations and the corresponding geographic coordinates for 4 points on the map. I usually use 4 UTM grid line intersections from the 4 corners of the map.
  • Map Name : A name for the map. This is name under which the map will show up on your phone.
  • Destination Directory : Where the final geo-referenced and converted map should be placed.
  • Multilayer : Select this and all the different zoom levels. This is especially useful for large maps as it speeds up the on-the-phone zooming by storing multiple zoom levels in the final map.
  • Format : I usually use jpeg format as the resulting maps are smaller.

After filling in all the above hit the Create Map button and the geo-referenced map will be placed in the destination directory. There will be a directory containing two files <map_name>.otrk2.xml and OruxMapsImages.db . Copy the entire directory to the phone inside /mnt/sdcard/oruxmaps/mapfiles/ and the next time you open OruxMaps on the phone you should see the new map in the offline maps list.

Creating offline maps from online sources

The OruxMaps application can also use offline maps created from online sources such as Google Earth, Google Terrain, OpenSteetMaps, NRC Toporama and many others. The offline maps can be created directly on the phone using the Map Creator menu option, or with the Mobile Atlas Creator desktop application. Recent versions of MobileAtlasCreator have removed a large number of sources, you can use the version from here which contains more sources (including Natural Resources Canada Toporama).