ArduPlane: parameterize lookahead climb ratio

[timtuxworth]

Plane altitude terrain lookahead currently uses a fairly arbitrary but safe 50% factor when calculating the maximum pitch to assume when calculating the if the plane can safely fly over the approaching terrain.

Some users want to be more aggressive than the default. so this makes the 50% factor into a parameter. The default is no-change to current behavior, but by changing PTCH_LKAHD_CLMB users can now chose a more (or less) aggressive factor for the percentage of maximum climb factor to use when calculating terrain lookahead.

[timtuxworth]

Hi George - could you take a look? Any suggestions?

[Georacer]

Hi Tim!

I've tried to read and internalize the lookahead code, but it's quite opaque; in the way I understand it, it's plainly wrong.
So I probably understand it wrong.

But that means that I shouldn't just expect your intervention to have no side effects.

Instead, do you have any test results (logs), where before the plane wouldn't manage a climb and now it does?

[timtuxworth]

Hi Tim!

I've tried to read and internalize the lookahead code, but it's quite opaque; in the way I understand it, it's plainly wrong. So I probably understand it wrong.

No you have it right. I had to rewrite terrain lookahead in my terrain avoidance Lua script #28625 because of that. In fact the only thing I really want out of it is the parameter value :-), so that my Lua based lookahead can use the same ratio.

[timtuxworth]

But that means that I shouldn't just expect your intervention to have no side effects.

The code should have no side effects iff the default value is used, which should give the same results as the previous hard coded value.

[Georacer]

@timtuxworth I've spent some time parsing the code.

To me, it looks like if the ratio is 0, only then will the full climb rate be asked by the lookahead.

But I want to see comparative tests.
If you beat me to that, please post those logs.