doc:
You can create multilevel JNX file from Google Maps Tiles cache containing more zoom levels. Then, in Garmin device, each map level disappears at some map scale, as you zoom the map out.
Each map level in the JNX file has defined one parameter, which we call JNX scale. The table on page
http://whiter.brinkster.net/JNX.html shows relation between the curent scale setting of Garmin device (you can see it on device's display) and JNX scale seting.
When MOBAT2JNX creates multilevel JNX file from GMT cache, it has to insert the JNX scale parameter for each contained map level. MOBAT2JNX uses some standard settings. With -jnxscale parameter, user can influence, at which map scale the JNX map levels disappear from Garmin device's display. You can assume -jnxscale parameter as an coefficient.
From the MOBAT2JNX readme file:
The default multiplier for calculating JNX Scale factors is 130.2084.
You can also use "set jnxscale=180" in your
batch file or set the permanent environment variable.So MOBAT2JNX uses default JNXSCALE parameter value 130.2084. If your map level disappear at scale 300m, but you wish it to disappear at 800m, you can try to set the JNXSCALE parameter to 130.2084 * 800 / 300.
For an already existing JNX file, you can still adjust JNX scales of JNX map levels by using the jnxscale utility from
http://www.the-thorns.org.uk/mapping/help/jnx.html