Driving altitude via FSUIPC Offset 0x570

[bigskyfunk]

Does anyone know what this altitude is referenced to? Is it center of the earth? Radio Alt? Baro Alt?

I have a feeling it is radio alt and in that case I need to know the surface altitude so I can match the altitude generated by my sim which does not have a surface model.

Is there a way to extract the surface height below the aircraft using FSUIPC?

Thanks for you help as always.

Lance

[Skittles]

While going through the list of offsets, I thought I saw a Surface Height. I'll check again.

Is this what you're looking for?

Out of the Programmers.doc

Offset	Size	Use	                                                    FS2002	FS2004*
0020	  4	   Ground altitude in Metres x 256. (see also offset 0B4C)	Ok	    Ok

[Pete Dowson]

Does anyone know what this altitude is referenced to? Is it center of the earth? Radio Alt? Baro Alt?

Aircraft altitudes, like mountain tops and contours on maps, are of course measured from Mean Sea Level, as is this one. Why would you expect anything so wildly different from standard aviation (or even general) practice? Do you measure your home's altitude from the Earth's centre? :?

Is there a way to extract the surface height below the aircraft using FSUIPC?

It is available in two places -- 0020 and 0B4C. Both are listed. You can use them for radio alytitude calculations if you need such.

Pete

[bigskyfunk]

Pete thanks for your response and your comments on my hair-brained "center of the earth" idea. I tried using 0x020 to correct my altitude, but it does not appear to be dynamic. I logged the input and it stays constant during final approach even though the flight path is over some uneven terrain and water.

Then I logged the position and attitude parameters I am trying to drive. The log file shows that the altitude is only being updated about every 200ms. I am setting all the other parameters every 20ms. I have simplified the interface to FSUIPC so that all I do is read and write the position (lat,lon,alt) and attitude (phi,theta,psi), (ie offset 0x560 - 580).

Do you have any ideas on how to increase the update rate of altitude offset 0x570?

Also, I tried to use VDJKEY's idea about driving velocity and accelerations and letting FS9 do the integration, but it does not work at all.

Thank you for your help :)

[PhilippeV8]

It is available in two places -- 0020 and 0B4C. Both are listed. You can use them for radio altitude calculations if you need such.

Pete

:idea: 31E4 ? 8)

works fine here.

[Pete Dowson]

I tried using 0x020 to correct my altitude, but it does not appear to be dynamic. I logged the input and it stays constant during final approach even though the flight path is over some uneven terrain and water.

0x0020 is one of the original "un-mapped" FS values so it should be okay. When you say "correct" your altitude, you mean you are needing radar altitude? i.e. AGL? Try the one computed by FSUIPC at 31E4.

Then I logged the position and attitude parameters I am trying to drive. The log file shows that the altitude is only being updated about every 200ms.

Which, the one at 0020? That may just be an FSUIPC cycle for lower priority items. Clarify what you are talking about and I'll check.

Do you have any ideas on how to increase the update rate of altitude offset 0x570?

Is that what you think is updating only every 200 mse? As far as I know all the values for the 6 variables, LLAPBH are updated by FS every frame.

Regards

Pete

[bigskyfunk]

Pete and everyone,

With the aide of FS Interogater and this helpful community I finally realized that I was not driving the fractional portion of altitude, 0x570.

Basically I just had it scaled wrong and it was always zero. After logging and plotting the data I was writing to FS9 I looked at it with FS Interogater and saw that 0x570 was always zero. Then I applied the scaling obtained from FS Interogater and the problems is solved.

I really appreciate everyones helpful input.

Thanks,

Lance