class Region extends Model {
    // that one has a required zone attribute which is a Polygon
}

class Forecast extends Model {
    // that one has a required zone attribute which is a Polygon
}

class Boat extends Model {
    // that one has a required location attribute which is a Point
}

class WeatherForecastCreationObserver
{
    private NovaRequest $request;

    public function __construct(NovaRequest $request)
    {
        $this->request = $request;
    }

    public function creating(WeatherForecast $forecast)
    {
        $coast = Coast::find($this->request->input('coast_id'));
        if ($coast !== null)
        {
            unset($forecast->coast_id);

            // This is throwing an SQLException, see below
            // $forecast->zone = $coast->zone;

            // I can however make it happy by wrapping it inside a SpatialExpression
            // Remember this tweak #1 as I will refer to it in next observer
            $forecast->zone = new SpatialExpression($coast->zone);
        }
    }
}

Numeric value out of range: 1416 
Cannot get geometry object from data you send to the GEOMETRY field 
(SQL: insert into `weather_forecasts` (`timestamp`, `zone`) values 
(2020-02-18 00:00:00, (-16.3 16.28,-23 16.28,-23 14.45,-16.3 14.45,-16.3 16.28))) 
at /home/vagrant/code/vendor/laravel/framework/src/Illuminate/Database/Connection.php:669)

class BroadcastWeatherAlertObserver
{
    public function saved(WeatherForecast $forecast)
    {
        $boatsAtRisk = Boat::within('location', $forecast->zone)->get();
    }
}

Call to undefined method Grimzy\LaravelMysqlSpatial\Eloquent\SpatialExpression::toWkt() 
at /home/vagrant/code/vendor/grimzy/laravel-mysql-spatial/src/Eloquent/SpatialTrait.php:219)

public function toWkt()
{
    return $this->value->toWkt();
}