GPSrChive Discussion Forum

GPSrChive wrote: Mon Apr 08, 2024 8:11 pm The reason is that all (or most) third party maps secretly identify as CityNavigator maps, so when CN is toggled, they also are toggled.

Do you know which code that makes it to identify it as a City Navigator map? I'm pretty sure that the map developers didn't put it in by purpose...

GPSrChive wrote: Mon Apr 08, 2024 8:11 pm This has always been an issue with devices that allow maps to be enabled/disabled collectively.

I never noticed problems like this, although I don't have a GPSMAP 67. What I do know is that when you put multiple maps in one img file, you cannot switch individual maps on and off. Switching on/off is done per file. Maybe this is the case?

javawa wrote: Fri Apr 12, 2024 1:13 pm
Do you know which code that makes it to identify it as a City Navigator map? I'm pretty sure that the map developers didn't put it in by purpose...

It's more likely that Garmin has included identifiers in its own maps. The remaining maps are identified as CN.

The map format is reverse engineered pretty well. They would have noticed those identifiers.
Also note that the City Navigator maps use a different, compressed format (that's what 'NT' stands for). NT isn't reverse engineered, and isn't used by OSM map makers.

On a side note, using the same map ID (Family ID) as the CN map will certainly cause problems, but the chance that they are the same is very small.

javawa wrote: Fri Apr 12, 2024 1:13 pm What I do know is that when you put multiple maps in one img file, you cannot switch individual maps on and off. Switching on/off is done per file.

I agree with many of the arguments you presented, but I must say that there are Garmin devices in which disabling one map from the map set results in disabling all maps contained in that file.
Garmin devices use a solution that turns them on and off by map ID or by Map set (file name).

That's exactly what I meant to say...
Older devices turns them on/off by map ID, newer by map set.

javawa wrote: Fri Apr 12, 2024 1:33 pm The map format is reverse engineered pretty well.

Yes, pretty well, but not completely.

I have more time committed to learning Garmin map coding than all of the devices on this wiki. This is not a subject for casual study.

javawa wrote: Fri Apr 12, 2024 1:33 pm They would have noticed those identifiers.

Apparently not.

There are multiple methods used to embed the map ID into a Garmin map file. Not all maps use all methods. No doubt, some of them are used for security purposes to prevent theft, and as such I am unable to share more details at this time.

How can the map I create from scratch with a Garmin-independent compiler be related to the CN map?

Well, I've never experienced problems with a combination of CN and OSM maps on a device (I've got a few to test, and many GPS owners have used JaVaWa Device Manager to check their device for problems), as long as you keep in mind to store each map in a separate file for the devices that cannot handle multiple maps in a single file properly.
Also to be avoided: maps with the same family ID and map segments with the same segment ID.

Could it be related to the fact that the map is routable? I noticed that all routable OSM maps are turned off or on when toggling the CN map layer.

Can you create an online report with JaVaWa Device Manager? That might give some more information about your specific case.
There is a complication though, JaVaWa Device Manager cannot access MTP-devices like the GPSMAP 67. The solution is to put the SD card in a card reader connected to your PC, in that case JDM is able to access the SD card.