Import and Export

Sky Dolly supports a range of file formats for import and export of flight or aircraft data into (from) Sky Dolly.

Supported Formats

The following file formats are supported:

Format	Flavour	Description	Import	Export
CSV	Sky Dolly	Sky Dolly comma-separated values	yes	yes
CSV	flightradar24	flightradar24.com comma-separated values	yes	yes
CSV	Position	Position and attitude data	-	-
GPX	-	GPS exchange format	yes	yes
IGC	-	International gliding commission format	yes	yes
JSON	GeoJSON	GeoJSON	-	yes
KML	flightaware	flightaware.com KML	yes	-
KML	flightradar24	flightradar24.com KML	yes	-
KML	Generic track	KML with elements	yes	-
KML	Sky Dolly	Sky Dolly KML	-	yes

Formats

CSV - Comma-Separated Values

The CSV format (comma-separated values) is a simple text format organising the data into columns, containing an optional header with column names followed by values which are typically separated by a comma. There are however variants which use other delimiter characters, such as tab stops or semicolons.

GPX - GPS Exchange Format

The GPX format is an XML-based format for exchanging global positioning system (GPS) data (or generally speaking, position data recorded with any global navigation satellite system (GNSS)). Besides tracks containing the actual recored data the format also supports waypoints and routes, including some metadata.

The GPX format is an XML-based format for global positioning system (GPS) data exchange (or generally speaking, position data recorded with any global navigation satellite system (GNSS)). Besides tracks containing the actual recored data the format also supports waypoints and routes, including some metadata.

The <wpt> elements specify individual points of interest (e.g. start and end point, including waypoints along the planned route to visit)
The <rte> element contains the planned route to get from one waypoint to another
The <trk> element contains the actual recorded GNSS data (e.g. GPS data), the actual track that has been taken and recorded

IGC - International Gliding Commission

The IGC format has been specified by the International Gliding Commission. It is mostly popular for flight recorders used in gliders. The format is a text-based format and consists of various “records”, such as:

Header (H records): flight date, pilot name(s), used flight recorder hardware, and other flight data
Tasks (C records): the (planned) waypoints, including take-off and landing
Fixes (B records): the timestamp, location, pressure and GNSS altitude (plus optional extended data such as environmental noise level)

JSON - JavaScript Object Notation

The JavaScript Object Notation (JSON) is a text-based format designed for data exchange between applications while still being “human-readable” (to some degree). Like XML it merely specifies the syntax of a document, without specifying the semantics.

The semantic is injected by defining the proper keywords, objects and their hierarchies.

A notable example is the GeoJSON format, which specifies geographic features using the JSON syntax.

GeoJSON

The GeoJSON format represents geographical data such as points, lines and polygons, by using the JSON format. The format is maintained by the Internet Engineering Taskforce (IETF) and specified by the RFC 7946.

KML - Keyhole Markup Language

The Keyhole Markup Language (KML) format is used to specify and display geographic data with “earth browsers”. It has become well-known with the advent of Google Earth. The format is maintained by the Open Geospatial Consortium (ogc.org).

Import

In order to import a flight:

Choose the desired import format via the File | Import menu entry

An import dialog will appear, with common and plugin specific import options.

Common Import Options

CSV - Comma-Separated Values

The Format ooption specifies the column layout of the data.

FlightRadar24 - the data is in flightradar24.com column layout, essentially position, heading and velocity
Sky Dolly - the data is in Sky Dolly column layout, that is the entire data for the given aircraft

Note that while the Sky Dolly format contains almost all recorded aircraft data (position, engine, primary flight controls, ….) it does neither contain information about the actual aircraft type nor about the initial flight conditions (simulation time, temperature, pressure, …). But for the time being it is the format of choice to exchange aircraft for formation flights, recorded on different computers (e.g. in a multiplayer session).

IGC - International Gliding Commission

GPX - GPS Exchange Format

Options

The Waypoints option specifies which GPX element (<wpt>, <rte> or <trk>) to interpret as waypoint. Those positions are then stored in the flight as waypoints.

Waypoint <wpt> - the <wpt> elements are interpreted as waypoints
Route <rte> - the <rte> elements are interpreted as waypoints (default)
Track <trk> - the <trk> elements are interpreted as waypoints (less useful, but possible)

The Position option specifies which GPX element (<wpt>, <rte> or <trk>) to interpret as position. The imported latitude, longitude and altitude values are then stored for the aircraft as positions.

Waypoint <wpt> - the <wpt> elements are interpreted as positions
Route <rte> - the <rte> elements are interpreted as positions
Track <trk> - the <trk> elements are interpreted as positions (default)

So while the default settings interpret the GPX elements as specified (“as intended by the specification”) it is possible to import GPX data containing only a (planned) route (<rte>). So while those points are likely to be few, with a great distance between each, Sky Dolly will do its best to reconstruct the (planned) flight.

The popular Little Navmap application is able to export flight plans as GPX. The option to specify the Positions may be useful in such a use case.

KML - Keyhole Markup Language

The Format option specifies the KML format (flavour) respectively the source which created the KML file in the first place.

flightaware - the KML file as exported from flightaware.com
flightradar24 - the KML file as exported from flightradar24.com
Generic track - the KML file with a >gx:track< element

Export

In order to export a flight:

In the logbook (key F1), load the desired flight
Choose the desired export format via the File | Export menu entry

An export dialog will appear, with common and plugin specific export options.

Common Export Options

Formation Export

The formation export option controls how formation flights are to be exported:

User aircraft only - only the aircraft designated in the formation as user aircraft is exported
All aircraft (single file) - all aircraft of the formation are exported, if possible into a single file
All aircraft (separate files) - all aircraft of the formation are exported, each into its own file

Some file formats such as KML and GPX support multiple tracks, so they are suitable for exporting a whole formation into a single file. Otherwise each aircraft is exported into its distinct file, with an enumerated file name starting from 1 to N (the number of formation aircraft).

Sample Rate

Resampling is the process of calculating data points at a different frequency (in Hertz) than the original sample rate (also in Hertz). This involves interpolation of the original sampled values, to get another “smooth interpolation curve” through the new sample points. Various interpolation methods exist, such as linear and cubic interpolation.

Sky Dolly applies cubic spline interpolation (Hermite splines) for flight position, velocity and acceleration and mostly linear interpolation for instrument lever positions and flaps positions, for instance.

There are different scenarios where resampling is useful. The two major cases are upsampling (the data is evaluated at a higher frequency than the original sample rate) and downsampling (the data is evaluated at a lower frequency than the original sample rate):

Upsampling is done if the recorded data has been sampled only every second (1 Hz), but we need the data for every simulated frame (essentially in the same range as the displayed frames per second, but possibly even higher). So the data is resampled with, say, 60 Hz.
Downsampling can be done in order to reduce the amount of data. For instance if an aircraft was recorded in the flight simulator for every simulated frame (typically in the same range as the displayed frames per second, possibly even higher), but for data analysis reasons it may be sufficient to have the aircraft position sampled only every second (1 Hz). In essence that means a data reduction by a factor of 60 in this example.

The sample rate option specifies the resample rate in Hertz:

1/10 Hz (smallest resulting file size), …, 10 Hz (largest resulting file size)
Original data (no resampling) - the original recorded data is exported, without any resampling

A sample rate of 1 Hz is typically a good choice when it comes to visualising or even analysing flight paths. Choose original data in cases where you want to transfer data from one Sky Dolly instance to another one.

CSV - Comma-Separated Values

Options

The Format option let’s you choose between various column layouts:

Sky Dolly - all simulation variables supported by Sky Dolly are exported
FlightRadar24 - the CSV has the same columns and values as also exported by flightradar24.com

GPX - GPS Exchange Format

Options

The Timestamps option let’s you choose the base time of the exported timestamps:

Simulation time - the time as set in the flight simulator is taken as start time
Recording (real-world) time - the actual real-world time is taken as start time (the point in time when the recording was started)

The option Recording (real-world) time may become useful if screenshots are taken during flight recording. With the help of the exported GPX with real-world timestamps the photos may then be “geotagged” with the help of other third-party software.

IGC - International Gliding Commission

Options

The Pilot name specifies the name of the first pilot. The name is exported in the header (H record: “pilot in charge”).
The “Co-pilot name* specifies the name of the second pilot. The name is exported in the header (H record: “crew 2”)