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  1. #21
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    Tested in original US 40 and converted AU 50>52. Screenshots are from the 40, but results were identical in the 52.

    The Dual map and original J014709.JCV file give this message predictably:

    2sm5

    Substituting the patched JCV:

    qmwo

    Manually scrolling thru the route [south on Suk Sawat Road]:

    e8c6 61nk 739z

    As the map and jcv are on a microSD, I also tested it in a AU 1390. The expected results as experienced with US 3597, crashed with both original and patched JCV file when a view was encountered on a simulated route. The crash & reboot error on 1xxx devices has been longstanding, being repeated with subsequent fw versions when using an Asian jcv file. Any hope that Garmin will correct this 'bug' in either 1xxx or 3xx7 fw is probably in vain i guess unfortunately. Seems that if a non-Asian device displays a blank or message screen but does not crash when trying to show a view, then the patched file will work fine. On the evidence so far, if there is a crash error using original JCV with the device that'll be repeated with the patched file.
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  3. #22
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    Great explanation Neil, and I am now happy I have got my friend to purchase the 52 for me in Oz.

    Just need to wait for February now, when he arrives.

  4. #23
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    Quote Originally Posted by Neil View Post
    .................. Seems that if a non-Asian device displays a blank or message screen but does not crash when trying to show a view, then the patched file will work fine. On the evidence so far, if there is a crash error using original JCV with the device that'll be repeated with the patched file.
    Curse my eternal optimism. I've just disproved the first part of that theory using a US 765. Black screen using original TH jcv file and exactly the same on switch to patched. Went to the trouble to load SG/MY fw for test using it forgetting that it will display TH jcv anyway. Original and patched TH jcv of both the THGLB and J014709 [even worse of course] show cr*p views [picture size is lower than optimum]. Pleasant surprise was that when using SG/MY fw with AU map the TTS is perfect unlike with SG/MY fw on US/EU/AU 2x5. It even seems smoother than US 4.50 fw with loading and scrolling and the high-res AU jcv is crisp and perfect.

    Seems like a 'lucky dip' with US fw devices whereas Asian fw is good. I'll report on use with other US fw devices as I can. Then maybe you can collate the results to let ppl know what will and won't work syzygy.
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  5. #24
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    Quote Originally Posted by Neil View Post
    Seems like a 'lucky dip' with US fw devices whereas Asian fw is good. I'll report on use with other US fw devices as I can. Then maybe you can collate the results to let ppl know what will and won't work syzygy.
    The rule of thumb is: What you get with the original JCV is what you get with the patched JCV except the copyright warning picture is replaced by the actual junction view picture.

    As explained in post #16, the patch only deals with pointer replacements. No other changes like decryption are made to the original JCV file. So if a firmware can display the copyright warning picture then it will be able to display the replaced picture at the same quality (be it crisp, crappy, or black, etc.). Similary, if a firmware has problems (like crash) to parse and display the copyright warning picture then it will have the same problems with the patched pictures. The patched JCV cannot do better nor worse than the original JCV to access a picture.

  6. #25
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    syzygy can you give us some info about JCV format when you can time for it. Especially I am interesting in picture coordinates with format and offset rules for extracting it...
    Love your wife? Buy yourself a GPS for answering to her favorite question: "Dear, where are you?".

  7. #26
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    Thanks syzygy, i've got it now sorry for being a bit dense before. I thought if the 'foreign' jcv was not parsed correctly it would always simply crash the unit as would of course the patched file, and thought displaying either blank or pirate screen would result in correct display of patched. I completely missed the point that a blank screen is also a parsing error like crash error.

    Confirmed so far:

    All Asian fw units seem capable of correctly displaying another Asian locale's patched jcv.
    US 765 shows black screen
    US 1xxx have crash error.
    US 2xx5 display patched correctly.
    US 3xx7 have crash error [also therefore probably dezl 760].
    US xx [tested 40/50/42/52] display patched correctly.

    Further testing now done:
    US fw 2350, 2460 [also therefore probably dezl 560], 3790 all cannot parse Asian file, they display blank screen [almost certainly a generic problem with all 2xx0 and 37x0 series US/EU].
    US fw 3490 & 3590 display pirate screen with original, correctly display the patched file.
    US/EU 2xx7/2xx8 have crash error.

    Tested Fix for US 3790 is to convert to US 3490.
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  8. #27
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    The tool works great with CN Thailand 2013.30 on StreetPilot 2.16 for Android.

  9. #28
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    Quote Originally Posted by Giomen View Post
    syzygy can you give us some info about JCV format when you can time for it. Especially I am interesting in picture coordinates with format and offset rules for extracting it...
    To extract a picture, firstly get the starting file offset and length of the image block at the following file offsets. All uint32 are in little endian order.
    Byte Offset of JCV File in Hex Type Name
    2F uint32 image_block_offset
    37 uint32 image_block_length
    3B uint8 image_xor

    Secondly, divide the image block into a sequence of image records. Each image record has the following format with variable length.
    Byte Offset of Image Record Type Name
    0 uintVAR image_length
    VAR / 8 uint8[image_length] image_data

    To find the values of VAR (i.e. size of image_length in bits) and image_length follow the algorithm below.
    1. In the first byte of an image record, count n = number of consecutive least significant bits with value 0. For example, if the first byte value equals to 5c in hex then n = 2.
    2. VAR = (n + 1) * 8
    3. Convert the first n+1 bytes of an image record in little endian order to an integer N. For example, if the first 3 bytes are 5c 7e a4 in hex then N = a47e5c in hex.
    4. image_length = N shifted by n+1 bits to the right. For example, if N = a47e5c in hex then image_length = 148fcb in hex.


    Thridly, for each byte B in image_data replace B by the value "B xor image_xor". That's all.

    Note that the image_data you get may be a JPG or PNG image, or a SVGZ file (a compressed SVG text file which describes the layers of a junction view picture and refers to other JPG and PNG images). A JPG or PNG image in turn can be a complete or partial (i.e. one of the layers) junction view picture. Lastly, one of the JPG or PNG images in the Asian JCV files of post #1 is the copyright warning picture.
    Last edited by syzygy; 1st January 2014 at 22:20.

  10. #29
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    Default Units known to be compatible/incompatible with Asian JCV files

    Quote Originally Posted by Neil View Post
    Confirmed so far:

    All Asian fw units seem capable of correctly displaying another Asian locale's patched jcv.
    US 765 shows black screen
    US 1xxx have crash error.
    US 2xx5 display patched correctly.
    US 3xx7 have crash error [also therefore probably dezl 760].
    US xx [tested 40/50/42/52] display patched correctly.

    Further testing now done:
    US fw 2350, 2460 [also therefore probably dezl 560], 3790 all cannot parse Asian file, they display blank screen [almost certainly a generic problem with all 2xx0 and 37x0 series US/EU].
    US fw 3490 & 3590 display pirate screen with original, correctly display the patched file.
    US/EU 2xx7/2xx8 have crash error.

    Tested Fix for US 3790 is to convert to US 3490.
    zumo 3x0 use same Western JCV as US/EU nuvi xx so they are also compatible with patched Asian files:
    Quote Originally Posted by Neil View Post
    ......... add US/EU zumo 3x0 to that list too thanks to [Only registered and activated users can see links. ].
    Well done, Neil! A very nice summary of the compatibility of Asian JCV files.

    Here is my theory of this compatibility issue, including CN Europe JCV files. As mentioned in post #28, a junction view picture actually consists of layers of JPG or PNG images, including (from bottom to top) background (day or night), roads, arrows and road signs. There are, however, at least 3 different ways to describe this layered structure of a junction view.

    The first kind is by a SVG text file which has referencs to the image of each layer. The second kind is by an array of pointers where each pointer points to the image of a layer, from bottom to top. The third kind is a special case of the second kind with two layers only.

    Not all firmware support all kinds of layer structures, hence the compatibility issue arises. The result of a firmware parsing and displaying an unsupported layer structure is unpredictable. It may skip, display a blank picture, or in the worst case crash and reboot.

    One good example is the JCV files of CN Europe 2014.30. All NT versions are in the first kind. All NTU versions are also in the first kind except one of them is in the second kind. Guess what? The Nuvi 4x/5x firmware supports the second kind only. That's why you cannot install a NT map with a working NT JCV file on Nuvi 4x/5x. You have to install the NTU map with the only NTU JCV file of the second kind.

    All and only the Asian JCV files in post #1 use the third kind where the lower layer points to a complete junction view image and the upper layer always points to the copyright warning image. On a normal device that supports the second kind (such as Nuvi 4x/5x) the upper layer will override the lower layer such that the copyright warning image is always displayed. On a device with localized firmware the upper layer is skipped so the lower layer image can be displayed. As you may have guessed, the patch simply replaces the upper layer pointer with the lower layer pointer.

    Now, back to Neil's nice summary we can see
    All Asian fw units support the first and second kinds (the third kind is implied).
    US 765, 1xxx, 2xx0 (e.g. 2350, 2460), 3xx7, 37x0 (e.g. 3790) support the first kind only.
    US 2xx5, 3490, 3590 support at least the second kind.
    US 4x/5x support the second kind only.
    dezl 560, 760 support the first kind only.

    Lastly, here is the algorithm to tell if a JCV file is the first or second kind
    1. Convert the first two bytes at file offset 0 in little endian order to an integer N1.
    2. Convert the 4 bytes at file offset 0x56 (or 86 in decimal) in little endian order to an integer N2.
    3. If N1 >= 0x5e (or 94 in decimal) and N2 is not zero then it is the first kind. Otherwise, the second kind.
    Last edited by Neil; 16th October 2014 at 02:10. Reason: add info for zumo 3x0.

  11. #30
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    pity we don't have a LIKE button actually , I would have given a LIKE to syzygy's post
    Edit: done now
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