Why does OLC display wrong altitudes?

On Tuesday, February 12, 2019 at 11:22:19 AM UTC-5, wrote:
Here is an example:
https://www.onlinecontest.org/olc-3....l?dsId=6604692
- at the time 18:11:04 the altitude displayed in the web page is 68 meters (which is well underground), while the IGC file (downloaded from OLC) says "A0086400944" at that time, i.e., about 900 meters.

....and here I was thinking "I don't know what he's on about... all *my* flights display correctly". lol. New issue. Have you been in touch with OLC?

T8

On Tuesday, February 12, 2019 at 11:43:19 AM UTC-5, Tango Eight wrote:
On Tuesday, February 12, 2019 at 11:22:19 AM UTC-5, wrote:
Here is an example:
https://www.onlinecontest.org/olc-3....l?dsId=6604692
- at the time 18:11:04 the altitude displayed in the web page is 68 meters (which is well underground), while the IGC file (downloaded from OLC) says "A0086400944" at that time, i.e., about 900 meters.

...and here I was thinking "I don't know what he's on about... all *my* flights display correctly". lol. New issue. Have you been in touch with OLC?

T8

It's not new, I've seen this many times for at least the last 2 years, starting before the switch from OLC 2.0 to 3.0. I don't know how to contact them.

On Tuesday, February 12, 2019 at 12:50:58 PM UTC-5, wrote:
On Tuesday, February 12, 2019 at 11:43:19 AM UTC-5, Tango Eight wrote:
On Tuesday, February 12, 2019 at 11:22:19 AM UTC-5, wrote:
Here is an example:
https://www.onlinecontest.org/olc-3....l?dsId=6604692
- at the time 18:11:04 the altitude displayed in the web page is 68 meters (which is well underground), while the IGC file (downloaded from OLC) says "A0086400944" at that time, i.e., about 900 meters.

...and here I was thinking "I don't know what he's on about... all *my* flights display correctly". lol. New issue. Have you been in touch with OLC?

T8

It's not new, I've seen this many times for at least the last 2 years, starting before the switch from OLC 2.0 to 3.0. I don't know how to contact them.

I've sent mail to olc.

T8

I’ve seen this occasionally in my flights if the takeoff altitude was not determined correctly, or if I forgot to start the logger before the tow started. I dont recall if it is OLC or the logger which adjusting your takeoff altitude to airport altitude, but if there is mismatch there, the rest of the altitude trace will be wrong.
The solution is to edit the flight in OLC and manually adjust the start to your release time, which seem to fix this issue.

Ramy

On Tuesday, February 12, 2019 at 12:52:05 PM UTC-5, Ramy wrote:
I’ve seen this occasionally in my flights if the takeoff altitude was not determined correctly, or if I forgot to start the logger before the tow started. I dont recall if it is OLC or the logger which adjusting your takeoff altitude to airport altitude, but if there is mismatch there, the rest of the altitude trace will be wrong.
The solution is to edit the flight in OLC and manually adjust the start to your release time, which seem to fix this issue.

Ramy

Ah. On the flight log Moshe linked, the "flight" starts in the air. That must be it. I had some sort of pre start screw up that caused me to have to restart the flight recorder and (unusually) it did not do its normal thing and give me a take off to landing log with a short gap.

T8

On Tuesday, February 12, 2019 at 1:09:57 PM UTC-5, Tango Eight wrote:
On Tuesday, February 12, 2019 at 12:52:05 PM UTC-5, Ramy wrote:
I’ve seen this occasionally in my flights if the takeoff altitude was not determined correctly, or if I forgot to start the logger before the tow started. I dont recall if it is OLC or the logger which adjusting your takeoff altitude to airport altitude, but if there is mismatch there, the rest of the altitude trace will be wrong.
The solution is to edit the flight in OLC and manually adjust the start to your release time, which seem to fix this issue.

Ramy

Ah. On the flight log Moshe linked, the "flight" starts in the air. That must be it. I had some sort of pre start screw up that caused me to have to restart the flight recorder and (unusually) it did not do its normal thing and give me a take off to landing log with a short gap.

T8

A couple of other example such logs I've looked at also are missing the takeoff. So that may be part of the problem. But missing the takeoff is no excuse to mess up the altitudes in the fixes that do exist. Here's another example, and this one is from a logger (Dell Streak running XCsoar, AFAIK) that does not have a pressure sensor, both altitude fields are identical and contain the GPS altitude (which should never be "corrected"?):
https://www.onlinecontest.org/olc-3....l?dsId=4917557
- the altitudes in the first hour are displayed way too low in the OLC web page graphics.

On Tuesday, February 12, 2019 at 1:38:28 PM UTC-5, wrote:
On Tuesday, February 12, 2019 at 1:09:57 PM UTC-5, Tango Eight wrote:
On Tuesday, February 12, 2019 at 12:52:05 PM UTC-5, Ramy wrote:
I’ve seen this occasionally in my flights if the takeoff altitude was not determined correctly, or if I forgot to start the logger before the tow started. I dont recall if it is OLC or the logger which adjusting your takeoff altitude to airport altitude, but if there is mismatch there, the rest of the altitude trace will be wrong.
The solution is to edit the flight in OLC and manually adjust the start to your release time, which seem to fix this issue.

Ramy

Ah. On the flight log Moshe linked, the "flight" starts in the air. That must be it. I had some sort of pre start screw up that caused me to have to restart the flight recorder and (unusually) it did not do its normal thing and give me a take off to landing log with a short gap.

T8

A couple of other example such logs I've looked at also are missing the takeoff. So that may be part of the problem. But missing the takeoff is no excuse to mess up the altitudes in the fixes that do exist. Here's another example, and this one is from a logger (Dell Streak running XCsoar, AFAIK) that does not have a pressure sensor, both altitude fields are identical and contain the GPS altitude (which should never be "corrected"?):
https://www.onlinecontest.org/olc-3....l?dsId=4917557
- the altitudes in the first hour are displayed way too low in the OLC web page graphics.

And here's another example (one of my own flights this time), this log also is missing the takeoff, and in this case the whole (fairly short) flight displays with wrong altitudes. Near the end of the flight the OLC web page graph shows negative altitudes, landing at -561m - while the lowest altitude in the actual log (as downloaded from OLC) is +165m. It's all GPS altitudes, no pressure sensor in my Nook.
https://www.onlinecontest.org/olc-3....l?dsId=6600502

Those concerned have also sent a monetary contribution to OLC I assume. I need to send something for the year also!
Mark

On Tuesday, February 12, 2019 at 12:52:05 PM UTC-5, Ramy wrote:
I’ve seen this occasionally in my flights if the takeoff altitude was not determined correctly, or if I forgot to start the logger before the tow started. I dont recall if it is OLC or the logger which adjusting your takeoff altitude to airport altitude, but if there is mismatch there, the rest of the altitude trace will be wrong.
The solution is to edit the flight in OLC and manually adjust the start to your release time, which seem to fix this issue.

Ramy

Ramy: I think you're on to something there, as all the examples we've found seem to be of log files that are missing the takeoff. Although the effect of the "start" altitude on the displayed altitudes seems to dissipate later in the flight. But when you manually choose the start point, do you have to tell OLC the altitude of the start, or does the act of choosing that point tell it to believe the altitudes in the log?

I think they should always assume the altitudes in the log file are correct (for use in the web-page display). Even if the location of the start of the log is not at the declared airport. Certainly they shouldn't assume that the altitude of the start of the log is that of the airport, when the location is clearly not at the airport.

Moshe, I am not sure if correcting the start always fixes the issue, although it did for me in few cases, not sure exactly how.
Regardless, one would always check that OLC identified the release correctly and adjust if needed, otherwise this may significantly impact your score.

Ramy