Radar altitude is displayed at the mid-point, when below 200 feet a vertical bar moves up and down the scale which represents 200 ft AGL. Additionally a caret (triangle) moves up and down the scale, each small tick marks indicates 100 feet per minute with a maximum climb/descent of 1000 fpm.
Above 1428 AGL the digital display is removed.
Barometric altitude is your altitude above sea level as derived from a reference air-pressure and atmospheric laws. The result is your height above sea level regardless of your height above the ground. This is displayed above the VSI scale. In the example below my test map is at sea level so the baro and radar alt are the same. One of the things we'll do later is add a quick function to change the pressure to adjust this reading.
Another feature is that at some angles of bank, the AGL will vanish when this data is unavailable from the AircraftState (which is what happens when the ground moves out of the line of sight of the the radar altimeter under the aircraft when banking hard).
I'm not too clear what the angle of bank is, but I'm setting it to 30 degrees to match the bank angle indicator.
I noticed an inconsistency between the HMD VSI and the new one. The scale needs some testing with a stopwatch.
*update*
Today seems to have flown by as my laptop fan needed to be put out of my misery. Getting at the fan in a Qosmio X300 seems to require complete disassembly from the top down. In the process I managed to wreck the surface mount wi-fi connectors, a replacement antenna is on the way. Other than that I managed to get it all back together again with no major difficulty. Except I don't relish doing it all over again next week when the new parts arrive. The fan was truly dying, re-seating with machine oil didn't help.
It's 22:00 in the evening and I'm assessing where I left the FLT page, what's left to do.
- FPI flight path indicator
- Virtual waypoint marker
- Combined Torque
- Stabiliator gadget
That's more than I thought. Two of those are pretty quick to add. The difficult one, the virtual waypoint marker is a problem, I'm going to leave it out. My reasoning is that I don't have enough data on how it works with and without the video underlay.
The Stabiliator gadget will be handy to see the angle for debug purposes. It's controlled by the model LUA and you send messages to set an angle and it does it's thing. But it can be added later when required.
Lets get to work on the combined torque and FPI.
* edit *
Actually, I don't see an FPI in the source image so I guess I'll leave it out too (even though I just added it, I'll comment out the code).
* edit *
Actually, I don't see an FPI in the source image so I guess I'll leave it out too (even though I just added it, I'll comment out the code).
In the long previewmovie earlier released (with a nice flight over the city) I noticed that altitude rapidly changed when flying over buildings, and it rised or even disappeared when doing a hard turn. Your desciption explains this behaviour, but is this also how it works in real life?
ReplyDeleteId think they would have found something to fix this, as your altitude readout is false when turning (or even not available)? Isn't that a dangerous situation?
rised....rose...(?) I hope you know what I mean ;)
ReplyDeleteThe radar altimeter will do all manner of wounderous things to justify it's expense and bulk to maintain accurate output. I doubt it's like a laser measuring tape which is how I simply implemented it.
ReplyDeleteI really don't know how the real box works other than it looking quite chunky in google images. It appears to be a squarish bulk under the tail where it joins the main fuselage, looks like it has a window in it.
If I had to guess, it would sweep an arc, taking a cross section of samples and returns a weighted average. Still restricted by the physical constraint of being bolted onto the underside of a rolling chopper it will have a small field of view.
If I was smart I'd simply curve the last good value (like I do with the rate of climb) so the radar alt would not bounce so much. It's a trivial addition. The most accurate way would be do have three beams and taking the average but it all comes at the cost of cpu cycles.
I remember asking about this a while ago, specifically if the altitude changed as you rolled and the answer was maybe.
Personally I liked having direct feedback for flying over models so I could tell how big they were.
Flying a helicopter IS a dangerous situation, my advice is don't try it at home ;)
"In the long previewmovie earlier released (with a nice flight over the city) I noticed that altitude rapidly changed when flying over buildings, and it rised or even disappeared when doing a hard turn. Your desciption explains this behaviour, but is this also how it works in real life?
ReplyDeleteId think they would have found something to fix this, as your altitude readout is false when turning (or even not available)? Isn't that a dangerous situation? "
thank for share.
A question on al old blog entry. There's been some code changes since.
ReplyDeleteThe radar alt sensor has since been changed so it more consistent and will always return a valid distance while the aircraft is within pitch and roll limits. But will still vanish as is appropriate.
In the real aircraft the flight computer does some math to smooth it out (but doesn't update as fast as it does in the game). The readout will cut out beyond certain bank and pitch angles. If a sensor or gimbal is out of parameters you don't want it displaying false data which can be potentially more dangerous.