Thursday, 31 July 2008

Medion MDPNA150 sat nav device

A Medion MDPNA150 sat nav came my way in an IIC case the other day. It didn't have any IIC stored upon it but whilst I had it I thought I would look at the recovery of navigation data should one come my way requiring this.

The sat nav had a 256mb mmc card and it also had internal memory. Like the Navman's I looked at earlier the Median runs a Windows CE OS and the internal memory could only be accessed via Mobile Device Centre in Vista (probably Active Sync will suffice but I did not test with this). The navigation software is Destinator. As it turned out I found only one file of note on this particular device - Previous.dat. This file contains the history of locations previously navigated to and was stored on the memory card. Destinator does create other files of potential interest but they seemed to be missing on this sat nav.

The format of Previous.dat is of particular interest and differs from many other sat navs in the form it stores latitude and longitude co-ordinates. Most others I have seen before store these values as signed 32 bit integers. Within this file they are stored as a Double.

The structure of file seems to be as follows. There does not appear to be a header. The file starts with the first record and all records appear to be variable in length.

Each record begins with a type which I believe relates to the various navigation options. The type is stored in unicode and in my limited sample I saw:

(name of a Favourite)

The type is terminated with hex 0000.

A number of other zero terminated unicode strings may follow relating to House Number, Street, City and postcode.

Each record contains two sets of longitude and latitude co-ordinates stored one after the other. I speculate that one set is actual and the other set is nearest road. In my sample they were either very similar or the same. Each longitude or latitude value is stored as a double which requires 8 bytes therefore 32 bytes are required to store both sets. The two sets are followed by a further 16 bytes of data -use unknown, which completes the record.

To locate these co-ordinates I found it easier to count back from the start of the following record. The other problem to overcome is how to convert the doubles to a decimal value. Encase does not have a easy way to do this. The data interpreter in Winhex can do this. The hex editor 0xED on a mac can also do this but rounds up to fewer decimal places than winhex.

20th November 2008 Update
Subsequent to writing this up I examined a Goodmans device also running destinator software. I have written about it here . There is more information in that post. I can supply an Enscript (written by my friend Oliver Smith over at Cy4or) to parse out these records on request.


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