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keesverruijt / BR24radar_pi

OpenCPN radar plugin for Navico Broadband Radars (BR24, 3G, 4G models) [HISTORIC]
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What exactly are "spoke meters"? #299

Closed msacarny closed 5 years ago

msacarny commented 5 years ago

When digesting spoke packets, range in "spoke meters" is converted to 'actual' meters. What exactly are spoke meters, and why was range expressed in them as opposed to standard meters?

douwefokkema commented 5 years ago

From where do you get the term "spoke meters"? Unknown to me. In the spokes as received from the Navico radar, the range is encoded in decimeters, which we convert to meters.

msacarny commented 5 years ago

Thank you. Let me clarify. For example, we command range = 500 m.

As I see it, 4G packet headers are interpreted as follows: In br24Receive::ProcessFrame(), line 240: large_range is determined to be 0x80 raw_range = small_range = 0x0ca0 = 3232 range_meters = range_raw / 4 = 808 Line 287: m_ri->ProcessRadarSpoke(..range_meters..) Line 483: m_range.Update(convertSpokeMetersToRange(range_meters)) Here, 808, apparently in 'spoke meters' is converted back to 500 m by table lookup.

Why does the radar return such strange units for range in the packet header? What is the relationship between 'spoke meters' and 'actual' meters?

Hakansv commented 5 years ago

"Why does the radar return such strange units for range in the packet header?" Why?? Ask Navico. It is as it is. Here we just try to interpret. Why do you ask? BTW. BR24radar_pi is so to say out. At least for OCPN v5.0 and up. Try https://github.com/opencpn-radar-pi/radar_pi

douwefokkema commented 5 years ago

msacarny, The BR24radar_pi code base is old and no longer maintained. We have not been using this code base for over a year now. If you have issues, please refer to the current radar_pi code. Douwe