Canvas Tile Element

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Early Terrain radar emulation (from the 787-8)
Cquote1.png Drawing an entire image via setPixel calls from Nasal will also be slow [...] I would suggest, it might be better to make these special image layers which are computed by C++ code, so they can be updated efficiently.
— James Turner  (2018-12-02 11:16:35).  [Flightgear-devel] Feature request: Canvas dynamic image from Nasal.
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Cquote1.png Once you get to the extra features (of modern avionics), like FIS-B weather or TIS-B traffic info over ADS-B, or TAWS This is a link to a Wikipedia article (terrain alerting), we're probably in way over our heads trying to emulate even the simplest general-aviation IFR GPS.
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Cquote1.png A moving map is a different beast. It would make sense to implement that as a scene graph in its own right with its own pager. That would require a change in current fg architecture to use a CompositeViewer instead of a single Viewer, but we're contemplating that anyway.
— Tim Moore (2008-08-04 09:43:37). [Flightgear-devel] Cockpit displays (rendering, modelling).
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Cquote1.png I'd really like to use the Atlas generated maps as a layer in the browser map. Is anybody out there looking for an adventure and is able to modify the Atlas map generator to generate maps on-the-fly?
— Torsten (Mon Mar 17, 2014 8:56 pm). Re: Atlas still in use?.
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Atlas map view of the San Francisco bay area

Some contributors have been experimenting with atlas based moving map displays (with pre-rendered Atlas images), but with nasal code.[1] [2]

The nice thing about Atlas is that it uses the current FlightGear scenery for generating it's maps. If we get better scenery, Atlast produces better maps.[3]

This issue of not being able to render maps to a sub window is coming back to bite us every time. If it's not stuff like this then it's moving map/GPS/ND type instruments. [4]

James originally implemented the a moving navigational Map as a custom PUI widget - it's *not* an Atlas-replacement, or an MPMap replacement, i.e. not intended to also display terrain elevation [5]

An Atlas- style renderer as another layer is possible, it'd also let people builda 'map' dialog box with navaids and airways overlaid, like the map UIs in MSFS / X-Plane / Fly. [6]

In order to feed imagery from tools like Atlas or moving maps in general from a network server, you'd want to look at protocols like WMS and the servers which already have been developed for this purpose.[7]

the Atlas project already has a GetMap application, linked with CURL to to do the http requests... written by Fred back in 2004 [8]

Intro

The zkv 1000 glass cockpit project (2010)

tiled web maps are obviously great for many reasons, but people without a broadband internet connection may still want to use a different tool, or even an offline solution in general. And like I said, there is the issue of mismatching data - FlightGear has never been particularly good at this, but there is now an increasing tendency to rely on "online functionality", i.e. there is a growing assumption that people do have an internet connection, and that they're online while using FlightGear - depending on whom you ask, that is not just controversial, but increasingly problematic.


Apart from that, there is the issue that some of our really long-term contributor are in fact behind GSM-style connections, as well as a growing number of hard-coded online assumptions that have hit the project repeatedly - remember the METAR URL issue ?

Bottom line, it's not a good idea for the project to rely so much on infrastructure and make connectivity assumptions, FlightGear must remain usable in offline mode.

Atlas/Map can help the project to remain/become self-sufficient (again).

We've previously seen how this reliance on online infrastructure can hit the project really hard and affect the project for years to come (mapserver).

It isn't too far-fetched to suggest that sooner or later the project's increasing tendency to add functionality with a focus on people being online, will leave some people out of the loop.

Absorbing atlas back into the project can help the project to become self-sufficient again.

[9]

Problem

A simple, canvas based tile map which is centered around the aircraft.
MapStructure OSM (OpenStreetMap) layer created by Stuart for his ongoing FG1000 effort


Thanks to the Canvas system, we now have an increasing number of MFDs/avionics that use so called "slippy" maps - there remains the obvious issue that such a "slippy map" will usually be based on very different geo data than FlightGear's terrain (i.e. mismatching data).[10]

FlightGear uses relatively old data pulled at the time from X-Plane (IIRC). This data is not updated regularly because this could cause conflicts with the (also relatively old) scenery.[11]

More and more Airports that have different airport data on the FG Map & Route Manager. Route Manager data seems to agree with other map sources like Sky Vector. Does FG Map get updated from independent sources like Sky Vector & others.[12]


About setPixel()

Drawing an entire image via setPixel calls from Nasal (for terrain / wxr radar overlays by any chance?) will also be slow, in which case, it might be better to make these special image layers which are computed by C++ code, so they can be updated efficiently.[13]


Obviously, it's a valid use-case, i.e. creating a ‘scanned’ terrain radar, WXR or similar overlays on Canvas, no argument there, where defining a raster via paths is pretty heavyweight for frequent updating. [14]

For features like:

  • Inverse synthetic-aperture radar
  • Synthetic-aperture radar
  • Ground radar
  • Ground radar for moving objects


But once we got capability for modifying canvas images real-time or through some other method like fragment shader, it will be usable for many things, for example wxr radar etc etc.[15]


Originally, radar altimeter was a big CPU hit, because it does a ‘scanned’ set of 3D ground intersections (over a range of angles in two axes) at the full FDM rate (120Hz), and this becomes significant number of triangle intersections.[16]


This kind of feature would be the prerequisite to get a working TERRain mode on the 737 MAP display.[17]

Status

07/2020

Note  This can already be done by treating the tile as a 3D model and rendering an orthogonal projection of the tile(s), and using the patch from Howto:Extending Canvas to support rendering 3D models

RFC (idea/feature request frequently discussed on the devel list and forum)

To be fair though, depending on the progress in the scenery department (adopting Virtual Planet Builder), the atlas based approach may become obsolete sooner or later: World Scenery 3.0 roadmap

Background

FlightGear uses very outdated navigational data - whereas online sources (chart providers) use different data.

To solve this, we need to use the same underlying data source.

The most straightforward option would be to procedurally render our own charts using the map/atlas tools, and use those internally, without relying on 3rd party sources, and online web services.

Motivation

There is the long-standing idea to use FlightGear itself to render a map to a texture, e.g. based on the atlas/map source code (GPL compatible), quoting TorstenD:

What I have in mind for the map is to render the map tiles (small 256x256px fragments of a map) from flightgear scenery data on the fly when the user requests them from within the map application. Thats how openstreetmaps works and I like the idea of reusing proven concepts. There is no need at all - in fact, it's not even desireable - to do that in the main loop. Running a standalone application (or call it process if you like) creating and serving the tiles will add no load to the FlightGear process, no matter how complex the map is.[18]


Note  Porting Map.cxx into a dedicated ReaderWriter plugin for OSG by merging it with the existing STG/BTG ReaderWriter machinery in SimGear, we still end up with a mechanism that runs outside the main loop for loading/rendering, even if we're going through Canvas::Image or a subclass of it, because osg::Image objects are loaded by a worker thread.

Idea

1rightarrow.png See Atlas for the main article about this subject.

Given that we do have existing code to render such maps, and that the Canvas system does have support for loading raster images (sc::Image), this would be the most straightforward option to ensure that there is no mismatch between a moving map and a corresponding radar display, because it'd be using the same underlying terrain/vector data.

Integrating Atlas

Note  Also note that, while atlas may seem huge/complex and archaic, all that is needed is porting Map.cxx - which is really just 600 lines of self-contained C++ code, because it's a standalone executable - and it deals with all the parsing/scenery processing using atlas APIs, so given that it's designed to run in a separate process, it could also easily run outside the fgfs main loop, i.e. as part of an OSG ReaderWriter plugin, at which point it would become trivial to also support BTG files at the canvas/image level, because the plugin would process the BTG files using Map.cxx: https://sourceforge.net/p/atlas/hgcode/ci/default/tree/src/Map.cxx

This would also mean that Phi could use an atlas/map based back-end for the creation of maps based on actual FlightGear scenery, as per Torsten's original idea.[19]

atlas isn't "obsolete" - it just works "as is". What it provides ? A moving map, and in fact an accurate moving map - because it contains its own terrain processing routines that "parse" FlightGear scenery/terrain to render moving map charts interactively, and it does so in a different process (out of the FlightGear main loop), so can easily use other cores.

These days, it may admittedly seem redundant and even irrelevant thanks to options like Phi and/or Azure. But the truth is, atlas remains relevant, because it processes actual FlightGear terrain files to create those charts, but also because it's an "offline" application, you don't need a high bandwidth internet connection - it will even work without an internet connection.

As a matter of fact, the right thing to do would be absorb atlas/map into simgear and use it in-sim to dynamically create charts "on demand", which would then include "up to date" airport charts (think runways, taxiways, frequencies etc) - but that would also mean updating atlas, because it's still from the early pre-OSG days, i.e. is using legacy OpenGL[20]

Pointers

References

References
  1. https://sourceforge.net/p/flightgear/mailman/message/20010870/
  2. https://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg33880.html
  3. https://www.mail-archive.com/flightgear-devel@flightgear.org/msg16345.html
  4. https://www.mail-archive.com/flightgear-devel@flightgear.org/msg30262.html
  5. https://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg27097.html
  6. https://sourceforge.net/p/flightgear/mailman/message/20012110/
  7. https://sourceforge.net/p/flightgear/mailman/message/28301870/
  8. https://sourceforge.net/p/flightgear/mailman/message/28302153/
  9. https://forum.flightgear.org/viewtopic.php?f=31&t=37158#p364650
  10. https://forum.flightgear.org/viewtopic.php?p=364640#p364640
  11. https://forum.flightgear.org/viewtopic.php?f=25&t=37589&p=369707#p369706
  12. https://forum.flightgear.org/viewtopic.php?f=25&t=37589&p=369707#p369705
  13. https://sourceforge.net/p/flightgear/mailman/message/36483136/
  14. https://sourceforge.net/p/flightgear/mailman/message/36483231/
  15. https://sourceforge.net/p/flightgear/mailman/message/36484679/
  16. https://sourceforge.net/p/flightgear/mailman/message/36484933/
  17. https://sourceforge.net/p/flightgear/mailman/message/36579110/
  18. https://forum.flightgear.org/viewtopic.php?f=31&t=21972&p=203544#p203544
  19. https://forum.flightgear.org/viewtopic.php?f=31&t=21972&p=203544#p203544
  20. https://forum.flightgear.org/viewtopic.php?f=31&t=37158