CSBK data and repeater GPS coordinates

[Zaarin]

Apologies if this is a really obvious question but I can't find a straight answer.

Been trying to get CSBK data working with enhanced GPS and MNIS. In the MNIS configuration where I configure conventional systems, there's a table for adding GPS coordinates of the repeaters at the bottom. The only thing I can find in the system planner is the following:

The location information is compressed into a single CSBK, and recovered at the control
station or MNIS with the location information of the repeater. IPSC/Capacity Plus Multi
Site does not work with a control station for location CSBK data, because the control
station does not know where the location data comes from. However, IPSC/Capacity
Plus Multi Site works with the MNIS.

So what is actually sent from the radio that also requires the coordinates of the repeaters to work? Does it use some triangulation where it combines partial location data from the radio with the coordinates of the repeater to arrive at the actual location of the radio? Sounds overcomplicated.

 

[motoapx]

Based on my read of the system planner, it stands to reason that certain data is intentionally omitted from an LRRP response in order to fit into the CSBK data window. I'm just spitballing here, but I would think that you could fulfill that requirement doing something like this:

During initial registration (or the time that a LRRP request is sent to the radio), I suspect that the infrastructure sends its stored repeater coordinates to the subscriber. That information, alongside the subscriber's GPS-derived location, would allow the unit to calculate the delta of the two positions (probably a decimal lat/lon difference -- guessing the report is precise to the thousandths place due to the cited error of the lat/lon with CSBK), and send only that information back to the infrastructure in the CSBK response. At extreme latitudes I'd expect this method to break down (since 130 lateral miles at polar latitudes can span something like 20 degrees longitude), but I didn't see where / if the planner cites an upper or lower latitude limit for this mode.

In any case, this should be reasonably straightforward to test empirically if you have your infrastructure up and running. First set the repeater's coordinates to its actual location, and plot the reported location of a fixed GPS subscriber that is participating in the system. Then, change the repeater's coordinates (either lat or lon) by a known amount, and query the same subscriber for location information again (it's probably sensible to power cycle or reboot the participating equipment between trials). if the fixed subscriber moves by the same amount that the repeater was "moved", that seems like a pretty good indication that the mathematical difference of positions is what's being sent to the infrastructure in the LRRP response.

 

[Zaarin]

Thanks. Finally got a new server with SmartPTT and MNIS up and running today so I'll experiment a bit like you suggested.