C2 latitude longitude to TPPos conversion error

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CSeguinot
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C2 latitude longitude to TPPos conversion error

Post by CSeguinot » Mon Mar 29, 2021 11:33 pm

Hi all
Thanks to information given on this forum, I'm able to read .fpl, .trn, .cup and .apt files.
I'm using python code for this, without using Condor DLL, simply because I'm running Condor2 under Linux (and using DLL there is tricky).

Using some flight plans created under C2 for the 0.5 FRN landscape, I'm able to compare TP position, TPPosx and TPPosy :
1- given in the .fpl file (generated by Condor2)
2- and those calculated by converting latitude longitude (.apt or .cup files).

I generally get a good agreement with an error lower than 1 meter for most airports. However, for some airport the error rise to 20 meters which is not so problematic in most case but is not normal.

I don't think this comes from the fact that FRN landscape cover 3 zone (30-32). I already checked that .cup and .apt files have the exact same latitude/longitude. I already checked my latitude/longitude to UTM/WGS84 conversion (error is lower than 1 meter).

Does anyone knows what and where this error come from?

Regards,
Christophe (newbie in C2)

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dgtfer
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Re: C2 latitude longitude to TPPos conversion error

Post by dgtfer » Tue Mar 30, 2021 9:50 am

CSeguinot wrote:
Mon Mar 29, 2021 11:33 pm
Using some flight plans created under C2 for the 0.5 FRN landscape, I'm able to compare TP position, TPPosx and TPPosy :
1- given in the .fpl file (generated by Condor2)
2- and those calculated by converting latitude longitude (.apt or .cup files).
for some airport the error rise to 20 meters which is not so problematic in most case but is not normal.
I don't think this comes from the fact that FRN landscape cover 3 zone (30-32). I already checked that .cup and .apt files have the exact same latitude/longitude. I already checked my latitude/longitude to UTM/WGS84 conversion (error is lower than 1 meter).
Does anyone knows what and where this error come from?
Hi Christophe,
Could you tell us where these errors are located?
Have you tried another conversion method, for example with Marc Till's CoCoCo (COndor COordinates COnverter)?
When we have merged the various sceneries in a single big one, we have also noticed a few misplacements, some of about 20m...
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CSeguinot
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Joined: Fri Nov 13, 2020 6:56 pm

Re: C2 latitude longitude to TPPos conversion error

Post by CSeguinot » Tue Mar 30, 2021 4:16 pm

Hi,
Thank you for this rapid answer.

This error is present on some airport. For 'Montlucon-Gueret' which is in zone 31, the error is 20 meters.

I understand that some airport could be missplaced on the maps, ie placed at an unprecise location while creating the landscape.
But I don't understand why :
  1. Condor2 use Latitude longitude to convert to x,Y:
  2. C2 use this for creating Flight Plans (TPpos)
  3. taking (TPPosx, TPPosY) given by C2 FlightPlan I should be able to calculate precisely Airport latitude/longitude.
The only difference in my approach (as compared to what most tools are doing) is that I don't use NaviCon.dll , but my own conversion tool which is working for most airports.

I will investigate more deeply and try to give an exhaustive list off error, also try CoCoCo as well.
I czan send you a private mail with the error list when available.

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dgtfer
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Re: C2 latitude longitude to TPPos conversion error

Post by dgtfer » Wed Mar 31, 2021 8:04 pm

CSeguinot wrote:
Tue Mar 30, 2021 4:16 pm
I will investigate more deeply and try to give an exhaustive list off error, also try CoCoCo as well.
I czan send you a private mail with the error list when available.
Yes please, it can be helpfull.
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CSeguinot
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Re: C2 latitude longitude to TPPos conversion error

Post by CSeguinot » Wed Mar 31, 2021 10:27 pm

OK Things are now clear.

For airport contained in .apt, TPPOsx TPPOsy found in C2 .fpl are identical to those calculated from latitude longitude, within less than 2 cm error (the precision of UTM formulas used for converting)
For most airports contained in.cup files the error generally rise up to 1 or 2meters. This is normal, latitude longitude use decimal minute with 3 digit. So this error is consistent since 1/1000 minute correspond to 1.2 meter move. Also, latitude and longitude given in .apt and.cup files differ this is where my problem is.

I intuitively thought that when defining flight plan in C2, .cup airports provided by the user would be used prior to .apt landcscape airports which are part of the landscape.
However, C2 first use landscape airports and seems to forget .cup airports having the same name. In some case (FRN Scene, Montlucon-Gueret and Troyes airports) coordinates differs in .apt and .cup files (with respective 'error' of 21 meter and 262 meter along X direction). For those airports, .apt seems to refer plane track, and .cup glider track.

So there is no real error, just different positions in .apt and .cup files.
To what extent .cup airport are usefull if we can't override .apt airports?

I finally also discovered that .cup file are save in user turnpoints folder at the fisrt use, and this is the place where we can modify these files. (see viewtopic.php?f=37&t=19428)
If for example "Troyes" airport in .cup (user turnpoints folder) is rename to "Troyeszzz" I'm now able to see it. Whitout renaming it I only see Troyes found in .apt

Seems this description correspond to the normal C2 behaviour and that I'm learning by doing...
Regards, Christophe

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wickid
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Re: C2 latitude longitude to TPPos conversion error

Post by wickid » Wed Mar 31, 2021 10:46 pm

The Condor airport centerpoint is the middle of the takeoff runway as defined in the landscape editor (the blue rectangle in the landscape editor). This may not necessarily be the airport reference point which is what a CUP file would use. For my home airfield we have 3 runways. In Condor there is only 1 defined. So the airport in Condor is offset by about 200 meters to the north from the .cup file which has the airport in the center of our field.
PH-1504, KOE
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EDB
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Re: C2 latitude longitude to TPPos conversion error

Post by EDB » Thu Apr 01, 2021 5:10 pm

As what Wickid says, the take-off location in Condor is defined by the Landscape-builder and is the center of the defined take-off area. Usually the runway.

The way-point off an airport is defined by the ICAO as the ARP (aerodrome reference point). You can find the ARP in the AIP. This point is located near the initial or planned geometric center of the aerodrome and shall normally remain where first established...

So these locations are different...

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