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Garmin jnx file format hacking

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  • #46
    Re: Garmin jnx file format hacking

    Di they still say 'invalid file' - or just not display? Location is 36N 14E

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    • #47
      Re: Garmin jnx file format hacking

      "Invalid file" during the boot process.

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      • #48
        Re: Garmin jnx file format hacking

        So it needs more than the BirdsEye trailer, then

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        • #49
          Re: Garmin jnx file format hacking

          Two coordinates were missing from those files. Maybe this one will be better....
          Attached Files

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          • #50
            Re: Garmin jnx file format hacking

            Not better.... it doesn't work, always the same error message during the boot process. I tried the original file and also the renamed file to "Demo.JNX".

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            • #51
              Re: Garmin jnx file format hacking

              OK. I did some basic tests:

              - I use my demo.jnx file and I renamed it to Renamed.jnx. --> It works
              - I use my demo.jnx file (with 3 levels) and I change the first scale value to 76436. --> It works.
              - I use my demo.jnx file (with 3 levels) and I change all the scale values (73621, 4521, 341). --> It works.

              More tests to come...

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              • #52
                Re: Garmin jnx file format hacking

                Some more tweaks...
                Attached Files

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                • #53
                  Re: Garmin jnx file format hacking

                  Roger,

                  For Malta, please try to make a JNX file at scale 4777, with the tiles of size 0x20000 x 0x20000 coord. units.

                  Accoring to my tests, demo maps are really limited by the area.
                  Near Malta, if a map's coordinate box is 0x30000 * 0x30000 the map is valid.
                  0x40000 * 0x40000 - invalid,
                  0x30000 * 0x40000 - invalid,
                  0x20000 * 0x40000 - Ok,
                  0x20000 * 0x50000 - invalid,
                  0x20000 * 0x48000 - Ok,
                  0x48000 * 0x20000 - Ok.

                  So, it looks that for Malta, we can try to make a demo JNX with three horizontally aligned tiles with sizes 0x20000 x 0x20000, 0x20000 x 0x20000, and 0x8000 x 0x20000.
                  See the attached example: Victoria.zip
                  Last edited by Whiter; 13th December 2010, 02:23.
                  Garmin GPSMAP 62s

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                  • #54
                    Re: Garmin jnx file format hacking

                    I calculate x20000 as about 1km - is that right?

                    There are two maps here. The second one is located around 51.35N 2.98W
                    Attached Files

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                    • #55
                      Re: Garmin jnx file format hacking

                      Originally posted by roger47 View Post
                      I calculate x20000 as about 1km - is that right?
                      You are right. But this can depend on the latitude.


                      Originally posted by roger47 View Post
                      There are two maps here. The second one is located around 51.35N 2.98W
                      Both maps are shown without any problems. Here are the screenshots:Click image for larger version

Name:	gozo.jpg
Views:	1
Size:	8.0 KB
ID:	438921 Click image for larger version

Name:	462.jpg
Views:	1
Size:	8.7 KB
ID:	438920 Click image for larger version

Name:	565.jpg
Views:	1
Size:	12.4 KB
ID:	438919

                      gozo.jnx is 933 x 958 meters, st36.jnx is 820 x 929 meters.

                      Update:
                      And both maps are only displayed starting from zoom level 1.2 km.
                      Last edited by Whiter; 13th December 2010, 09:41.
                      Garmin GPSMAP 62s

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                      • #56
                        Re: Garmin jnx file format hacking

                        So what's next??

                        I think we can be reasonably sure that the images within a JNX must be aligned north-south so an image being converted must start that way or be rotated.

                        If anyone wants to send me a calibrated map (e.g Image + Ozi .map files) I can create a 1KM square JNX from it
                        Last edited by roger47; 13th December 2010, 13:15.

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                        • #57
                          Re: Garmin jnx file format hacking

                          Originally posted by roger47 View Post
                          So what's next??
                          There are several unknown things about the format:
                          1. The projection. You've said it's surely not Mercator. What can it possibly be? Do you know what projections are used in the Garmin devices? What are the most commonly used ones? If there is some criterion to distinguish, we can make any number of JNX files at different coordinates to check.
                          2. The set of scales. We've seen only four different scale values in JNX files. Are there other scales? To which zoom levels in the devices they correspond?
                          3. Max. number of levels of detail. How many levels does JNX format support? In all JNX files, I've seen, there were 3 levels at max. What if we need to have more?
                          4. The device lock code. How to sign a JNX file, so it would be accepted by a device?


                          Originally posted by roger47 View Post
                          I think we can be reasonably sure that the images within a JNX must be aligned north-south so an image being converted must start that way or be rotated.
                          You are right. There's no angles in the JNX format. At least, in the current version of the format


                          Originally posted by roger47 View Post
                          If anyone wants to send me a calibrated map (e.g Image + Ozi .map files) I can create a 1KM square JNX from it
                          I have a large collection of OZI maps, but they all are much larger than one square km. I've tried to cut a small piece from one of them, but the image quality was too low.
                          Garmin GPSMAP 62s

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                          • #58
                            Re: Garmin jnx file format hacking

                            1 The projection of the Garmin-produced maps is unusual - but I have seen it in other aerial images. The scale (in terms of degrees) is the same in Latitude and Longitude. This means that the images look stretched east-west. They are OK at the equator but the further north or south, the bigger the effect. The ones I produced are Plate Carree which means they have a consistent scale in metres/feet etc but the ratio of Latitude to Longitude is the cosine of the Latitude. The Garmin units must be correcting for their aerial images using the supplied coordinates but this does not, as you rightly say, allow for any rotation. Mercator projection (which stretches north-south) should work at these scales. But, who cares, as long as we have one that works.

                            2,3.I agree we need to investigate scales and zoom levels - but the Garmin units seem to be able to zoom themselves (as in your screenshots) so I reckon a map could be workable with just one supplied level. It's not ideal - but the restricted size of 'demo' maps is the more important problem.

                            4. Sorting out the size (which seems to mean the lock code) is most important. Do the lock codes interact with the map content - or is it possible to put new content under an existing lock code?

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                            • #59
                              Re: Garmin jnx file format hacking

                              Whiter : do you have a subscription to BirdsEye? If yes, are you able to produce a map, catch the lock code and use this one for a map created from scratch by you?
                              Last edited by Bill_clark; 16th December 2010, 00:44.

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                              • #60
                                Re: Garmin jnx file format hacking

                                Originally posted by Bill_clark View Post
                                Whiter : do you have a subscription to BirdsEye? If yes, are you able to produce a map, catch the lock code and is this one with a map created from scratch by you?
                                Yes, I do have a subscription, and a couple of days ago I've made a program to intercept WinInet.dll functions calls (BirdsEye interacts with the servers with WinInet
                                library). The signature block is sent by the server - all 788 bytes - and BirdsEye saves it to the JNX file wihtout modifications.
                                Right now I'm trying to disassemble the firmware. Unfortunately, I've never worked with ARM architecture.

                                One interesting observation: If you try to make two or more JNX maps with the same coordinates for the same device, the JNX files you'll get will ony differ in the signature block, all other header fields will be the same. The order of jpegs can possibly change, and map GUID will differ.
                                Now, if you cut the signature from one of this files, and palce into other, that modified file will be loaded and displayed without any error messages.
                                But this signature cannot be used in the JNX files made at different coordinates.
                                This means that the CRC in the header does not take into account the signature block, but the signature itself surely depends on the coordinates.

                                It would be very interesting to make two maps for the same place for two different GPS devices, and then to try to exchange their signatures.
                                Garmin GPSMAP 62s

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