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FSGRIDUK.TXT
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1991-02-08
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============================================================
Quick Basic programs for calculating Microsoft Flight
Simulator coordinates in the United Kingdom.
============================================================
The other-wise excellent Microsoft Aircraft and Scenery
Designer program (for use with Flight Simulator 4.0) has a
problem with coordinates. An option to use latitude and
longitude is offered, but does not work in the United
Kingdom area (perhaps the reason why it is not officially on
sale here!). This is a bit of a problem if, like me, you
wish to improve areas of the fairly barren UK scenery.
Microsoft Flight Simulator is still, to my mind, one of the
finest items of software available for the PC. I have never
really found computer games very satisfying, but FS (without
warfare) kept drawing me back. After finding I could do
consistent landings (without any idea what the flaps were
for) I started to wonder what the real thing was like. Eight
months and 4000 quid later, I now know. FS was not really
very useful in practicing general handling or visual
navigation, but now I am thinking of doing the IMC rating,
its radio-nav aspects have come into their own.
I could practice in the USA, but would prefer to fly in the
UK (I'll probably never actually fly outside it). So I need
to be able to improve my local flying area scenery using
ASD. When I first read about it, I hoped that the manual
would have data on the coordinate system and that I would be
able to compile numeric files into scenery. Unfortunately,
you have to create scenery in the ASD itself and there is no
information on the coords base. Finding that the Lat/Long
option was rubbish was another blow and the CAA charts don't
have an FS grid overlay (strange omission!).
I am a hydrographic surveyor and fairly familiar with
different coordinate systems, so I knocked together a basic
Lat/Long to FS program using a few points known in both
systems. It didn't work. After a week of exploring other
avenues, I discovered that one of the points I used -
Southampton VOR - is miles out of position in the FS world,
almost coincident with the Seaford VOR! FS-TEST acts as an
integrity check program to weed out any rogues.
Things are not perfect on the scenery disk, but these
programs seem to be correct to within about a hundred
metres. For the best accuracy, you should select points to
give a roughly equilateral triangle, containing the area in
which you wish to make conversions. Deviation angles between
the grids are shown to a decimal degree, but aerodromes are
probably best skewed to give the correct runway orientations
(as runways are quoted in magnetic this will not be much).
============================================================
FS-L2F allows on-screen conversion from Latitude/Longitude
to Microsoft Flight Simulator coordinates in the United
Kingdom area, primarily for use with the Aircraft and
Scenery Designer program. The Lat/Long coords are converted
to Ordinance Survey grid coordinates (using an algorithm I
was given some time ago by Dr Chris Davis of UWIST) and then
converted to FS grid by a transform using three points
(known in both OS and FS coords), fairly widely spaced
around the area in which conversions are required. These
must be edited into the file FS-OS.DAT. Input files (for
When compiled with Quick Basic the usage is:-
>FS-L2F [/P] [/O [resultfile]] [/I inputfile]
/P adds printer output
/O adds file output (defaults to FS-L2F.RES)
/I takes LatLong data from inputfile
Input files (for batch use) must be lines of text in the
form - "N5143.50, W00315.70".
============================================================
FS-O2F is a sub-set of FS-L2F which allows on-screen
conversion from Ordinance Survey grid to Microsoft Flight
Simulator coordinates in the United Kingdom area. The usage
is the same as FS-L2F, except that any input file should
contain `easting, northing' (eg "319428, 171973").
============================================================
FS-GRID uses a reverse transform (again with data from the
file FS-OS.DAT) to create a file of the FS grid
intersections of a given rectangle in terms of OS
coordinates. These could be plotted onto an OS map (or an
overlay) to allow you to read off FS coordinates directly.
============================================================
FS-OS.DAT is required by FS-L2F, FS-O2F and FS-GRID. It is a
list of points defined in FS coords and OS coords. Choose
three well-spaced points surrounding the area in which you
require conversions. Mark the three chosen with a `*' in
first position on name line. To add more points to this
list, you can get OS coordinates from published Lat/Long
(convert with FS-L2F) or OS maps, and FS from Flight
Simulator data sheets or slewing to recognizable places.
Watch out for obviously duff FS coordinates (Southampton VOR
is very wrong). In the Flight Simulator world VORs are set
on integer coordinates, so perhaps runway crossings may be
the best points to use.
============================================================
FS-TEST tests the integrity of the FS/OS coordinate data in
the FS-OS.DAT file by finding the distance between all pairs
of points in both FS and OS terms and finding the ratio
between them. Any ratios which stray from the mean scale
(268 metres per FS unit) are marked. Results are sent to
file FS-OS.ERR.
============================================================
FS-L2F.EXE is the compiled version of FS-L2F.BAS.
============================================================
While I am happy to allow free use and modification of these
programs, I retain the copyright.
============================================================
Andy Zienkiewicz
Cardiff
0222 794329
February 1991
============================================================