Radar Plugin Techical Details

[SerialHobbyist]

Just because I find it interesting, I'm trying to figure out how my Halo20+ radar "works".


Are there any references available?


Is someone who worked on the plugin willing to answer a few questions?


I'm trying to read the code but my C++ is rusty. I can see the data coming from the radar and the code seems to be storing it in 4k "spokes" (or maybe 2k?). Is a "spoke" of data a radial line from the unit with equidistant values for whether there is a "return" at that distance?


My test program receives the data, but it seems to receive 360 spokes in about 150ms which seems way too fast if each spoke is 1 or 2 degrees, so I'm pretty sure I misunderstand that part.



Is the spoke North up, or bearing up, or something else?


Thanks in advance for any insights.


Chas Douglass

[Hakan]

Chas..
First of all you may want to read a paper that was a inspiration for the Navico radar scanners plugin. Although the Halo code is not all the same the basics are there.

http://www.roboat.at/fileadmin/user_...kiEtAl2011.pdf

[SerialHobbyist]

Thanks so much. I think I can probably figure out the differences looking at the code.


I really appreciate the response.


Chas Douglass

[merrimac]

Chas,

You may have already understood this from the code, but the Navico radars actually send out 2048 ‘spokes’ per rotation, and yes, your understanding of a spoke is correct. The data contains 1024 different distances, with 4 bits per distance.

The spokes are generally ‘relative to to front of the radar’, but depending on the radar type they also get sent the actual heading and this heading is then retransmitted in the spoke header. This only starts to make a difference during the time that a ship is slewing from one heading to the next; a stable heading will negate any time difference between applying a heading correction to the received spoke.

[SerialHobbyist]

Thank you, that does help clarify.


Chas Douglass