Hi Everyone:

I am looking at the arducopter 2.0.55 code, trying to know in detail how the auto landing works. The following is verify_land function.

I found it difficult to understand the blue sentences.  It says "land at 1 meter per second", but the first equation does not seem so.  Also, in the second equation, why the velocity_land is updated like that? what is the physical meaning? In my understanding, the velocity_land drops gradually when it approaches the ground, is that correct?

Thank you in advance.

static bool verify_land()
{
    // land at 1 meter per second
    next_WP.alt  = original_alt - ((millis() - land_start) / 20);            // condition_value = our initial

    velocity_land  = ((old_alt - current_loc.alt) *.2) + (velocity_land * .8);
    old_alt = current_loc.alt;

    if(g.sonar_enabled){
        // decide which sensor we're using
        if(sonar_alt < 300){
            next_WP = current_loc; // don't pitch or roll
            next_WP.alt = -200; // force us down
        }
        if(sonar_alt < 40){
            land_complete = true;
            //Serial.println("Y");
            //return true;
        }
    }

    if(velocity_land <= 0){
        land_complete = true;
        //return true;
    }
    //Serial.printf("N, %d\n", velocity_land);
    //Serial.printf("N_alt, %ld\n", next_WP.alt);

    return false;
}