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1992-09-15
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.* This file should be SCRIPTable without the need for any changes
.* or any specific formatting options. It has been set up to be
.* printer independent as much as possible.
.pm 5
.rc 1 |
.hy off
.ll 73
:gdoc
:frontm
:titlep
:title GCP: A Great Circle Program
:address
:aline Release 1.1
:aline
:aline May, 1989
:aline
:aline
:aline
:aline Garry Barker, VK5BUB
:aline VNET SYDVM1(ABABARK)
:eaddress
.ri on
:etitlep
.ri off
.ju on
:preface
:p.This program was written for the potential benefit of all
amateur radio operators and may be distributed freely to anyone
interested. No responsibility is taken by the author with regard to the
accuracy, currency or usefulness of the program.
.rc 1 on
:p.The initial release of the program was an attempt to sample the
usefulness or otherwise of the program and to judge the
benefits of further development based on feedback (or lack of it)
and so, it had a few niceties omitted.
:p.The release discussed in this document (Release 1.1), incorporates
the following enhancements:
:ul compact
:li.Some performance improvements through improved mathematics
:li.A more consistent menu interface
:li.Removal of a printing bug
:li.Inclusion of degree marker numbers on the circumference
of the printed circle
:li.Ability for users to specify their own reference locations
for inclusion on the printed map
:li.Ability to exclude reference locations from the printed map
:li.Ability to specify spacing of radial markers in both degrees
and kilometres on displayed and/or printed map
:li.Ability to exclude radial markers from displayed and/or printed map
:li.Requirement for about 20K more memory (enhancement??)
:eul
.rc 1 off
:p.All work was done using the author's own time and resources.
The hardware included a PC1 with maths co-processor and
colour graphics adaptor, with 640K of RAM and 1 hard disk.
The printer used was a 4201 Proprinter.
:p.The mathematics for distance and bearing calculations were taken
directly from the :cit.ARRL Antenna Book, 14th edition, page
16-4.:ecit.
:h5.Acknowledgments
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:p.My thanks go to Garry Herden (VK5ZK), Hans Smit (VK5YX), Tony
Stanciewicz and Chas Franks for their help in testing and timing
the operation of the initial release of this program on their
equipment. Thanks also to those who offered suggestions and other
feedback on that release. It all gave me the incentive to produce
this next release.
.rc 1 off
:toc
:body
.* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
:h1.GCP Overview
:h2.Why a Great Circle Program
:p.The VK5BUB Great Circle Program (GCP) was written as a tool for
answering some questions I found myself asking, such as:
:ul
:li.How come I need to point a beam antenna due south from Adelaide
to contact Brazil? All atlas maps show Brazil either north-east or
north-west from Adelaide.
:li.Why do I hear strong Japanese signals when they are beaming long path
to Europe? Europe is "obviously" due west from Japan and Adelaide
is due south.
:li.How do I place my dipole so its major lobes favour
the "best" directions?
:li.Which signal paths lay over water?
:li.What countries are better worked on the long path?
:li.Why is it that I beam roughly north-west to Finland, but
.rc 1 on
Finnish
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stations beam almost due west for Adelaide.
:eul
:p.I found I could get hold of great circle maps from several sources,
but, in the true tradition of amateur radio, I wanted to be able to
produce my own and so I took it up as a project.
As with many projects, the program became a challenge and an interest
for me and I was unable to find anyone who had such a program. There
seemed to be programs to do one-at-a-time calculations of distance
and bearing, but none to draw pictures.
:p.In most instances, one would assume that the program would only
be needed once and then discarded once a basic map had been
printed. I suspect that the extra capabilities of GCP may make
repeated usage likely, although its usage on a one-off basis by
a few people would justify the effort to me.
:h2.What the program does
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:p.In essence,
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GCP allows the user to specify the latitude and
longitude of the centre of the circle and then
:ul compact
:li.draw a great circle map on a graphics monitor,
:li.draw it and then print it, or
:li.print without review on the screen.
:eul
The printed map in this
.rc 1 on
release, as for the previous release,
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of the program spans
4 print pages giving a circle of roughly 40 cm (16 in.) diameter.
The first 2 pages form the left half and the next 2 form the right
half of the map. The map is constructed by joining the 2
halves with glue in between the overlapping edges. See the section
on printer paper alignment in the chapter on "Using the Great Circle
Program" for a handy hint.
:p.At user request, the map can include a graphical representation
of the long path in the outer half of the circle with the short path
section then being half scale. This is useful in reviewing which countries
lie on a path all of its way around the globe.
:p.The printed map also includes numbered markers for a selected
set of locations to allow for easy identification of land masses
where the great circle representation makes shapes appear
distorted. At the bottom of the map is a legend for the
markers in numeric and concurrently alphabetic order.
.rc 1 on
:p.In this release, the markers and legend may be suppressed at
user option on the GCP menu. The particular locations to be used
as markers may also be changed by the user by editing the locations
source data file GCPLOCS.DAT. More on this later.
.rc 1 off
:h2.Required operating environment
:p.GCP has been written at the most machine-independent level
consistent with performance requirements. The lowest level
interfaces used are at the BIOS level for physical printing
and screen plotting.
:p.Basic machine requirements are:
:ul
:li.IBM PC or compatible.
.rc 1 on
:li.Approximately 430K of memory if maps are printed, 160K otherwise.
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This does not include memory needed for DOS, BIOS etc..
:li.CGA or similar if maps are displayed,
any other DOS-supported monitor otherwise.
.rc 1 on
Release 1.0 has been tested
with CGA, EGA and VGA, the latter running in CGA mode.
.rc 1 off
:li.IBM Proprinter or compatible if maps are to be printed.
Should work with IBM graphics printer. The printer must be LPT1.
:li.Room for the .EXE file and GCPMENU.PAN on floppy or hard disk
- approximately 80K. If the GCPLOCS.DAT file is used, it is accessed
every time printing is performed. If the file is not found, defaults
will be used, but if the drive is not ready, errors may occur.
This file is approximately 1.5K as supplied (unmodified).
:li.A maths co-processor is not needed, but provides a significant
performance advantage.
.rc 1 on
(See appendix A for some performance measurements for Release 1.0).
:li.Operating system - GCP Release 1.0 was tested with PC-DOS 3.2,
PC-DOS 3.3 and MS-DOS 3.3.
.rc 1 off
:eul
:h2.Required files
:p.The following are the program files:
:ul
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:li.GCP.EXE - the program for usage with maths co-processor. It will
either not execute, or run very slowly, if no co-processor
is available.
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:li.GCPA.EXE - the program for usage with the Alternate maths library
ie. without the maths co-processor. It will ignore a maths co-processor
if it is present.
:li.GCP.SCR - the documentation in standard GML SCRIPT format, suitable for
printing in virtually any SCRIPT environment
(PC, host, 3800, 3820, 3287, 6670...).
:li.GCP.LST - the documentation as a file to be printed to
a PC printer
.rc 1 on
:li.GCPLOCS.DAT - the source file of reference marker locations. This
may be modified by the user.
:li.GCPMENU.PAN - this is the compiled menu format. It may not be
changed by the user.
.rc 1 off
:eul
.* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
:h1.Using the Great Circle Program
:h2.Known bugs
.rc 1 on
:p.This release of the program has been released with no known bugs.
However, it has