X-Plane 11 incorrect altitude in position packets

[justinshannon]

Hi, xPilot developer here. I was debugging some X-Plane 12 altitude anomalies with xPilot this evening and I encountered a swift user that was sending a negative altitude in the velocity (and slow) position packets.

After the aircraft departed (KLAX), I noticed that the aircraft stayed low (glued) to the ground due to the negative altitude.

Log excerpt during the aircraft's taxi:

^GER1970:33.9402700:-118.3800400:-77.82:-179.34:4192072:0.0077:-0.0006:0.0010:-0.0000:-0.0006:0.0016:0.00
^GER1970:33.9402700:-118.3800400:-77.82:-179.34:4192072:0.0104:-0.0004:0.0017:-0.0000:-0.0002:0.0020:0.00
^GER1970:33.9402700:-118.3800400:-77.82:-179.34:4192072:0.0091:0.0004:0.0022:0.0000:-0.0000:0.0014:0.00
@N:GER1970:4772:1:33.94027:-118.38004:-78:0:4192074:78
^GER1970:33.9402700:-118.3800400:-77.82:-179.34:4192072:0.0091:0.0004:0.0022:0.0000:-0.0000:0.0014:0.00
^GER1970:33.9402700:-118.3800400:-77.82:-179.34:4192072:0.0061:0.0012:0.0031:0.0000:0.0009:0.0022:0.00
^GER1970:33.9402700:-118.3800400:-77.82:-179.34:1864:0.0073:0.0012:0.0044:-0.0000:0.0015:0.0015:0.00

Log excerpt after takeoff:

$CQGER1970:@94836:ACC:{"config":{"on_ground":false}}
^GER1970:33.9391600:-118.3867900:-77.85:-182.63:4193220:-68.7297:-0.3319:-7.2618:-0.0306:0.0081:-0.0058:0.00
^GER1970:33.9391500:-118.3869000:-77.85:-182.64:4294966212:-69.2695:-0.2294:-7.2341:-0.0404:0.0069:-0.0040:0.00
^GER1970:33.9391500:-118.3869800:-77.85:-182.66:4290771908:-69.6267:-0.1361:-7.2270:-0.0411:0.0064:-0.0036:0.00
^GER1970:33.9391300:-118.3871300:-77.85:-182.64:4286577604:-70.3273:-0.1660:-7.2324:-0.0524:0.0062:-0.0049:0.00
^GER1970:33.9391200:-118.3872500:-77.85:-182.65:4278184900:-70.8487:-0.1231:-7.2175:-0.0550:0.0050:-0.0100:0.00
^GER1970:33.9391100:-118.3874000:-77.86:-182.62:4273990600:-71.5415:0.0047:-7.1978:-0.0562:0.0014:-0.0139:0.00
^GER1970:33.9391000:-118.3875200:-77.86:-182.64:4265601992:-72.0500:0.0562:-7.2124:-0.0611:-0.0004:-0.0162:0.00
^GER1970:33.9390800:-118.3876800:-77.86:-182.65:4257209288:-72.7159:0.3660:-7.2173:-0.0592:-0.0020:-0.0151:0.00
^GER1970:33.9390700:-118.3878000:-77.86:-182.66:4253014984:-73.2044:0.8299:-7.2123:-0.0484:-0.0034:-0.0131:0.00
^GER1970:33.9390700:-118.3878800:-77.87:-182.67:4248820676:-73.5170:1.1657:-7.2139:-0.0386:-0.0043:-0.0094:0.00
^GER1970:33.9390500:-118.3880400:-77.87:-182.66:4244622276:-74.1224:1.7584:-7.2213:-0.0297:-0.0050:-0.0003:0.00
^GER1970:33.9390500:-118.3881200:-77.87:-182.66:4244622276:-74.4191:2.0895:-7.2196:-0.0257:-0.0053:0.0008:0.00
@N:GER1970:4772:1:33.93905:-118.38812:-78:145:4244622276:78

I watched the aircraft for several minutes, but the altitude remained a negative value.

The user reported to me that they are using X-Plane 11, swift v0.12.72.