Georeferencing with OpenOrienteering Mapper

MapRun courses need a geo-referenced map file, with lat/long coordinates for the area covered by the map, and saved in Google's KMZ format. Jon Glanville has documented the process of doing this using OpenOrienteering Mapper (OOM) v0.9.5 or later. nb. versions before 0.9.2 have a bug which causes errors in the result. And you also need Google Earth Pro (GE) to identify geographic coordinates. You can start with any of a non geo-referenced OCAD or OMAP file, or a JPEG image, which you may have exported from a PDF map image, such as one used by Purple Pen.

Creating a Geo-referenced OMAP File and KMZ

I briefly summarise this process here (adpated and extended from Jon's guide).

  1. You need to open or load this starting file in Purple Pen, using one of the following as appropriate:
    OCAD or OMAP map file
    • in OpenOrienteering Mapper "Open an existing map ..."
    JPEG or PNG file
    • in OpenOrienteering Mapper "Create a new map ..."
    • Use Template -> Open Template to load the map image file, specifying the dpi and map scale
    • export it as a JPEG at 200dpi (eg, using Preview on a Mac, or other program with similar functionality)
    • then import as a template as for JPEG above
    Purple Pen map
    • in Purple Pen, use File -> Create Image Files to save the All Controls course, creating a JPEG at 200dpi (preferably one without controls)
    • then import as a template as for JPEG above
  2. Save or save as this map as an OMAP file
  3. Identify two points to use for the geo-referencing locations. Choose points that are far apart, and which you can identify accurately on the map and on a Google Earth image (I recommend adding placemarks at these locations on the GE image for future reference)
  4. In OOM move the pointer to each of the two selected points, and get the map coordinates of each (visible in the bottom right of the window). eg
    A = (-63.44, 31.41)
    B = (106.00, 25.43)
  5. Use Google Earth to get the geographic coordinates of these two reference points. I find this easiest if I add a placemark at each location, and then "Get Info" for each to see (and perhaps nudge to cleaner values) the coordinates for each point. eg.
    A = (-35.331238, 149.129181)
    B = (-35.334722, 149.147314)
  6. Using Jon's Georeferencing Calculator spreadsheet, enter the two sets of coordinates for the two selected points, as well as the map scale, in the 9 yellow boxes. Then note the calculated Rotation and Scale Factor in the blue boxes
  7. In OOM, select Map -> Georeferencing. In the dialog:
  8. You now have a geo-referenced OMAP file, which you should Save
  9. You can now also create a KMZ of this by selecting File -> Export as ... KMZ, specifying 150dpi and keeping the tiling default. You can then open this KMZ in GE to verify correct referencing of the map

Creating a Geo-referenced OCAD File

Since many orienteering maps have been created using the (very expensive) OCAD program, and may not be geo-referenced, it is highly desirable to be able save a geo-referenced OMAP file created from this, back as an OCAD file. However this has been tricky, as the OCAD file does not keep as much information as the OMAP file does.

  1. Open the geo-referenced OMAP file in OOM
  2. Select Map -> Georeferencing. In the dialog:
  3. Save As a suitable OCAD format file (11 or 12 usually). nb. You will get a warning dialog that information may be lost, that you have to accept (because indeed it is, sigh).
  4. Close and re-open this OCAD file
  5. Select Map -> Georeferencing, and note in the dialog that the Georeferencing reference point has been shifted to the (0,0) map location with the geographic coordinates suitably updated, but also that the auxiliary scale factor has changed
  6. You can now export it as a KMZ file, which you can check is correct in GE (seems is very close but not quite the same as the KMZ from the OMAP file)

Creating a KMZ using the MapRunners O-Utils Convertor

Versions of OOM prior to v0.9.5 did not support KMZ export. We were able to generate a KMZ using the MapRunners O-Utils Convertor, but some additional steps were needed, as it requires the map to be oriented to true north, and then exported as an image file with associated world file.

  1. In OOM rather than using the calculated Rotation as the map declination, select Map -> Rotate Map. In the dialog:
  2. Select File ->Export as Image. In the dialog: This will save both the JPEG image file and the associated JGW world file
  3. In your web browser, open O-Utils. In the "Create a KMZ file..." section:

Please send any comments, improvements, or other feedback to:
Guide last updated by: Lawrie Brown - Friday, 02-Jul-2021 18:03:38 AEST