[Feature] Polygon Exclusion Zones

[rhbvkleef]

It is sometimes useful (especially for fixed radar installations) to draw geographic zones wherein no ARPA takes place. A geographic polygon seems reasonably feasible to implement. From the propsed clients, SignalK (with the resources-provider-plugin and FreeboardSK) and OpenCPN (with OpenCPN Draw) support drawing polygons.

As @keesverruijt knows, I recently implemented this in a (private) fork of radar_pi using OpenCPN Draw to create the polygons. It is able to export these polygons as GPX files. I personally don't believe it is a good data format for in the API of Mayara, and I think GeoJSON Polygon is a beter format. Signalk's resources-provider-plugin also uses it for regions, which is a bonus.

Example uses

• Islands and shoals: It is fairly common with fixed installations that islands and shoals are detected despite an autolearning background being present. It is nice to be able to exclude those areas entirely from considerations instead of having to tune your radar and autolearning background around it: you already know that there are never going to be useful radar targets there.

... More?

[redhog]

Regarding islands and other geographic features, see my notes in #11

When using mayara together with a chart plotter such as opencpn it is theoretically possible (but hard) to get the coastline from their chart source and use that for filtering.

Whether that should be done inside mayara is another question - but if it is to done inside a separate signalk plugin then another problem crops up - signalk doesn't have a concept of a pipeline of filters on its data model, so not sure how this could work.