Maps and GPS - Calibrate a map


The main topic of this page is calibrating maps. In fact, this means that we build a relation between the pixels of image and their geographical coordinates. Further I will give you some additional data. On this place no large treatises on map projections, map dates and such. To do this, I refer you to the internet (Wikipedia). For converting geographical coordinates form one in an other format  you  can find sufficient information and tools to. Memory-map ®, Fugawi ®, PathAway ® and OziExplorer ® all have their own tools to calibrate a map. If these do not help, then you can do it "manually" by creating a JPR-file.


A JPR-file contains calibration for data map(-file). With this data programs like Memory-map®, Fugawi®, PathAway® and OziExplorer® (whether or not indirect) able  to locate a geographical coordinate in the right spot on the map. The file format was developed by Fugawi®, but doesn't support it anymore. The last version of the file description was "JPR file format Version 1.18". Maybe you can find this document somewhere on the internet. An older version (1.14) can be found on the PathAway website (JPR file format Version 1.14). On this websit is more interesting information about the JPR File format (Advanced Mapping Manual and PathAway Map Conversion Tools 3.0).

The following information is essential for building JPR-files: name of the map (nm), the map datum (dm), the map projection (pr) (coordinate system) with associated parameters (pp, zn and p1-p6) and at least 3 (reference) points (rp1, rp2, rp3, ...) on a map of which both the pixel coordinate and the geographical coordinates in latitude and longitude are known. This information may be supplemented with scale (sc), Pixel per Inch (sr), units of measurement (un, du), type graphics file (it) and the vertices of the polygon of the usable part of map (vp1, vp2, vp3, ...). For details, I refer to the documents mention above.

Building a JPR-file be aware of the following peculiarities.

  1. The JPR-file and the Graphics-file must share there file location.
  2. The JPR-file follows the rules of the English language. Where in numbers in continental languages commas is used, in a JPR-file are dots used and vice versa. Practical: the comma is used as separator between data and the dot is use decimal separator.
  3. Commas aren't used for thousends.
  4. Use a simple editor for creating and customizing your JPR-files. This prevents all sorts of unique "invisible" characters in the text (and much frustration in debugging). Personally I use Notepad® from Windows®.
  5. Latitude and longitude aren't noted in degrees, minutes and seconds, but in degrees decimal ( ##.##### ).
  6. Five digits to the right of the decimal point for latitude and longitude provide sufficient accuracy.