[mkgmap-dev] [PATCH] route recalculation sensitivity

Mon Apr 6 13:29:46 BST 2009

Bernhard Heibler wrote:
> Hi,
>
> I think I found the required bits. Seems to be the flag at 0x43 in the
> TRE header....
Tell you what, the code that handles the bytes at 0x47 and 0x48 looks
flawed to me.
Assuming 0x47 and 0x48 are a 16-bit number, mkgmap sets it to a constant
'1':

        writer.putInt(0x110301);

        writer.putChar((char) 1);

        writer.put((byte) 0);

        polyline.writeSectionInfo(writer);

But looking at Garmin's own maps, I see a variety of numbers coded here
in the range 0x4AE to 0x590....
(The following is a dump of the bytes at 0x43-0x46 and 0x47-0x4A
interpreted at 32-bit LE numbers)

Found  0: 0x110301 0x31000544

Found  1: 0x110301 0xC3000490

Found  2: 0x110301 0x8F0004CA

Found  3: 0x110301 0x03000564

Found  4: 0x110301 0xF3000590

Found  5: 0x110301 0xDF000524

Found  6: 0x110301 0x1D000505

Found  7: 0x110301 0x94000537

Found  8: 0x110301 0x0000053F

Found  9: 0x110301 0x3E000540

Found 10: 0x110301 0x5E00052F

Found 11: 0x110301 0x06000512

Found 12: 0x110301 0x2E0004F8

Found 13: 0x110301 0xCE0004FF

Found 14: 0x110301 0x880004EC

Found 15: 0x110301 0x320004F1

Found 16: 0x110301 0x9C0004BC

Found 17: 0x110301 0x240004F7

Found 18: 0x110301 0xA600050D

Found 19: 0x110301 0x040004CD

Found 20: 0x110301 0xBC0004EF

Found 21: 0x110301 0x36000526

Found 22: 0x110301 0x080004D6

Found 23: 0x110301 0x100004AE

Found 24: 0x110301 0x000004D8

So we see that Garmin themselves use 0x110301 at 0x43(!), it seems bytes
0x47-0x48 are a 16-bit number and presumably 0x49-0x410 are what mkgmap
gets from the call to "polyline.writeSectionInfo(writer);". The document
I have (John Mechalas, 2005) claims that 0x49 is actually constant '0'
and that the byte at 0x4A is the "Offset of Polyline Overview Section TRE4".

Steve