Why does OLC display wrong altitudes?

Many flights that I have looked at on OLC, posted by various pilots using diverse equipment, displayed with grossly incorrect altitudes. This is using the OLC online display that shows a small map and a small altitude graph. Usually, if incorrect, the displayed altitude in some parts of the flight is much (3x) lower than reality. If I download the IGC file from OLC and look at it in other software I can see the correct, higher, altitudes. Thus it is an OLC web page bug, not incorrect data in the flight logs stored on OLC. This has been happening for at least 3 years, in both OLC 2.0 and OLC 3.0. Is it just me? Is anybody working to fix this bug?

Metric system perhaps?

On Monday, February 11, 2019 at 3:11:44 PM UTC-5, wrote:
Metric system perhaps?

The altitude units (meters) are implicit in the IGC file format standard. And, as I wrote, the altitudes in the file itself, as downloaded from OLC, and in the online display, differ.

The wrong altitude is often about 3x too low, but that varies.

And the altitudes are displayed incorrectly only for some flights. I am not sure if the same flights always display incorrectly, and the other flights always correctly?

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.

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.

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 12:50:58 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

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.