GlobeCs v3 - What is it?

It is the 3D vector graph of the globe, 3rd version. The globe is turnable,  the display is zoomable and scrollable. Features to select view point, show the long-range fly path, put on the grid, crosshair, save the map, etc. Grey, auto scroll, transparent options.

Installation and use, legal status

Put files in the following directories: \APP\GLOBECS3.OPA, \OPD\GLOBECS.ODB, and with Psion-I (English version) install the OPA. It's all. I hope the menu  is self-explanatory enough.

GlobeCs is a Public Domain, if you use it, or its parts in your own programs,  please credit me. Use it as is, there are no registration and support for.

HW requirements

Psion3a (but I guess it runs on 3c and Siena too). Needs approx. 30-40 kB  memory to run, plus the PIC size, which depends on globe radius and the use  of grey (3.2-102 kB). It works on PC emulator without problems too (10-40 times quicker).

Features

• The user can jump to any view point in the Earth.
• It is possible to move the view point by optional 1,2,...,30,45 degree steps in N, E, S and W directions too.
• Thanks to vector graphics, the zooming is very easy.
• The optional globe radius is from 80 pixels (you can see the whole globe in the display) to 320 pixels (wider, than the 3a display, mainly for emulator on PC), varies with 40 pixels steps.
• The program calculates and plots the map outside the visible display too.
• After finish of plot the actual map can be saved as a PIC file.
• The ready plot of map is scrollable by arrow keys.
• The view point co-ordinates are always appearing in the saved filename...
• NEW in v2: and with the actual radius...
• NEW in v3: and plot time at the upper corners of map.
• NEW in v2: The initial view point is the home city, as in World app settings.
• NEW in v2: Long-range fly display. Input cities of fly departure and arrival and get the great-circle fly path. The calculated view point is at the middle of the shortest arch between the cities. The fly path looks as a straight line because the observer position is in the plane of the great-circle. It is fine to study the "strange" paths near to poles (e.g. Oslo-Seattle, Sydney-Buenos Aires). The city locations obtained from the ROM. Additional hints: (1) if you give the same city at departure and arrival, you can jump to it, (2) usually is enough to input the first some letters of city (e.g. "ams" for Amsterdam, "atl" for Atlanta).
• NEW in v2: Plot of the grid on the globe with optional 1,2,...,30,45 degree steps. Don't put on the grid after changing the radius without redraw!
• NEW in v2: Toggle the use of grey. If you use it, the required memory for the picture is doubled (the background space, the grid and fly line could be drawn with grey). Use redraw after toggle.
• NEW in v3: Interrupt of all plot activities by Esc key.
• NEW in v3: The user can scroll the map by arrow keys during the plot too.
• NEW in v3: Auto scroll option. If switched on, you see the recently drawn lines, i.e. the display follows the updated area of the map (the interrupt, plot time scroll and auto srcoll subjectively speed up the plot - no longer forced waits at apparently frozen display, you can break, interact or keep watch on the auto scroll; the cost for scroll is some 10 seconds, but you feel the scrolled plot quicker).
• NEW in v3: Transparent globe option. If selected, you can see the hidden continents too, like the globe would be made of glass. If grey is on, the hidden continent and lakes are appearing with grey, as well as the hidden parts of grid lines.

Menu short description

Size
    zoom In - increase globe radius by 40 until 360 pixels, redraw
    zoom Out - decrease globe radius by 40 until 80 pixels, redraw
    globe Radius - choose radius in range 80-360 pixels, default is 120

View point
    move to North by ... - move with the current step value, redraw
    move to East by ...
    move to South by ...
    move to West by ...
    Jump to co-ordinates - input longitude and latitude in degrees, South and West is negative, redraw
    Fly - displays the shortest fly path between two cities, input departure and destination city names

Options
    Grid on - puts the meridians and circles of latitude with step
    crossHair on - puts vertical+horizontal lines on the globe visible centre (view point)
    greY on/off - toggle the use of grey plane, default is on, redraw
    Transparent on/off - glass globe, hidden continents on the other side are visible too
    aUtoscroll on/off - during map plot the display window follows the plotting area

Action
    reDraw map - manual request for redraw e.g. after change radius
    save Map - saves the actual map in \PIC\ directory as picture
    change steP (for grid or move viewpoint) - possible steps: 1,2,...30,45 degrees, default is 15
    eXit - quit program

Help
    About - short message

Data representation and vectorization

The coastline of continents and islands and some big lakes is given like ODB file in binary form. Each point of the coastline represented by two integers (absolute longitude and latitude in degrees, West and South is negative), the end of a polyline indicated by two zeros. The usual step between the break-points is not greater then 7 degree (i.e. 3 bit, in this way it would be possible to save components of a relative vector with their signs in 1 byte, but the unpacking is a surplus time consuming procedure).

The data order, and so the plotting sequence of continents is the following: Africa, Europe, Asia, South America, North America, Australia and Antarctic (that's why the display is blank for a long, if the view point is e.g. on the West coast of USA or in New Zealand).

Some attempt made to keep continuos line even in case of near islands. In this sense I am proud of the Sumatra, Java and Lesser Sundaes, the British-Irish Islands as well as US-Canada Great Lakes but the Philippines turned out not very well. Presently the file consists more than 1500 points. By now some more or less islands in Arctic Ocean are missing, it means 300-400 additional points.

Computation and speed

The rotation of globe and calculation of visible/hidden points requires much trigonometry beyond the spherical-Cartesian transformation. For speed-up the code I used the following tricks:

• almost all often repeated calculations are in 2 or 4 byte integer arithmetic,
• pre-tabulated SIN for range 1-89 degrees with step 1, normalized to 1024 as integer, look-up of SIN and COS for any whole number degree angle in this table,
• procedure CACHEing.

The initial preparation of SIN table and dark background takes 7 sec. The time of plot recently is approx. 50 sec, does not depend on the globe size, and the view point. If auto scroll selected, the time is longer, about 1 min, and slightly depends on radius and view point. The plot time of grid strongly varies on step value.

Future plans

• to complete the missing islands' data,
• to load the initial map from PIC, if saved, instead of plot,
• to show the terminator - border of daylight and dark areas on the globe - depending on actual date and time in form of ellipse or sickle at the grey layer of bitmap; this could be processed and updated separately from the black layer,
• further probable speed increase by store instead of angles the normalized to 1024 SIN and COS values of longitude and latitude for each point,
• perhaps partial coding of plot routine in asm86 or C for further reduce the plot time.

The SIN normalization factor 1024 comes from the following considerations:

• this value is enough big to get accurate x and y co-ordinates on display (experiments made with 256, 512 and 1024),
• if you multiply 3 such normalized SIN or COS values, you are still in 4 byte long integer range, as far as 1024**3 < 256**4.

Bugs and known issues

In GlobeCs v1 fixed a small bug in saved map filename (sign of longitude part, i.e. E or W sometimes was wrong).

Known symptom is when changing the radius and then choosing "Grid on" the grid is drawn in the wrong size. This is not a bug: first you have to redraw the map. It would be easy to initiate automatic redraw, but due to plot time I decided to allow change more than one settings (e.g. step, radius, auto scroll) before next redraw.

Similar programs

D. Rushall's Solun 3 in registered version is able to show the 3D globe map. I have seen only its display hard copy, but as I understood, that globe is fixed size. Am I wrong? J. McAleey's W2 program does for 3D map the daylight/dark screen.