[mkgmap-dev] Opening gmapsupp.img with Basecamp?

Thu Apr 7 19:16:40 BST 2011

On Fri, Apr 1, 2011 at 2:59 PM, Andy Allan <gravitystorm at gmail.com> wrote:
> On Thu, Mar 31, 2011 at 6:34 PM, Steve Ratcliffe <steve at parabola.me.uk> wrote:
>
>>> I'm happy to do some more experimentation / testing patches etc if you
>>> can give me some things to try.
>>
>> Could you try the attached patch please.  If it works it should take it
>> up to 512M.
>>
>> If you need more than that there will have to be some experimentation to
>> find out what is implemented. Actual devices ignore all this as far as I
>> know.
>
> Initial testing is good - I got an image of 172M working fine. Thanks!
> I haven't yet tested all the way to 512M.
>
> It would be great for me if images up to 2G in total were supported.
> Next week I'll try Felix's suggestions of going via the mapsource
> installer and see if I can generate large gmapsupp.img files that big
> that Basecamp is happy with. That might give us some hints as to
> what's ultimately possible.

I spent a few hours on this today, but I couldn't get the nsis
installer working with large files - when I ran the .exe it would
crash complaining the installer was corrupt.

However, I did manage to get the nsis installer running and installed
a small (~121M) .exe file, and then used Basecamp to re-export that as
a gmapsupp.img (~173M, about 4k bigger than the one mkgmap produced).
I've spotted two interesting things about it

1) Basecamp won't re-import it the manner that it imports a gmapsupp
that mkgmap produces, which is annoying.
2) The values at OFF_HEADS and OFF_CYLINDERS are different and suggest
the upper limits aren't what we think

What's the etiquette for reverse engineering this stuff? Is it helpful
for me to post e.g. "hd gmapsupp.img | head -n 20" or is that a bad
idea?

Cheers,
Andy