[mkgmap-dev] Embedding raster maps

Tue Jan 5 12:02:06 GMT 2021

Hi Steve,

that was really helpful. I managed to get my map listed. However the raster layer did not show up :( Well I didn't really expect it. ;)

>
> I believe that the byte at 0x40 is the start block of the FAT so in
> test.img it should be 2.  Patching that byte did not make it load
> though.

Indeed, it seems to be an offset in number of 0x200 blocks. In all my example maps it's set to 8 and FAT starts at 0x1000. In your map it's set to 2 and FAT starts at 0x400. Another mystery solved.

I guess the next step is to get a rectangular extended polygon without the raster data to show up. The polygon type for the raster map tiles used is 0x10613. Usually it only contains a single point as the extended data referencing the jpeg tile has the four boundaries coded as 32 bit integers.

My goal is to remove the extended data and to code all 4 corner coordinates. This should give me a matrix of all rectangles. Again this raises the question about the minimum effort necessary to add a single polygon. In my naive point of view it would be just encoding it into the extended polygon section of the RGN file.  Of course I tried it and it does not work. So I am missing something, or have a couple of more bugs in my code.

Would it be possible to code another file with a single polygon

QPolygonF(
    QPointF(11.7914,46.9628)
    QPointF(11.8021,46.9628)
    QPointF(11.8021,46.9555)
    QPointF(11.7914,46.9555)
)

coded in three map levels: 0/24bit, 1/23bit and 2/22bit. This would give me a nice working reference to compare.

Thanks & Cheers

Oliver