PMGlobe, version 3.31 3 Aug 2009
[previous | contents | next]

Performance considerations

PMGlobe is designed as a ‘32-bit’ application, with all calculations being carried out using 32-bit integers (floating-point arithmetic is not used).

On slower processors, there may be a noticeable delay when the globe is drawn, especially if the window is large or fullscreen. The relatively long draw times are due to the number of calculations needed; for each pixel that is part of the globe, the program must determine the corresponding latitude and longitude, whether that point is land or water or is in daylight, twilight, or night, and how brightly it is lit (which depends on the angle of the surface of the globe at that point, relative to the sun’s current position).

In general, therefore, the simpler the image presented the faster it is drawn. Selecting Sunlight or 3-D both slow down the drawing. Similarly, non-equatorial (tilted) views take significantly longer to draw than equatorial views (hence the Snap to equator view option).

As a rough guide, the simplest (flat lighting, equatorial view, no sunlight) image with a diameter of 400 pixels would take about 4–6 seconds to draw on a 25MHz 386 PC or PS/2. On a modern 2GHz Pentium-based PC, this should reduce to about 60ms. The most complicated drawing (3-D shading, non-equatorial view, sunlight) might take about four times longer.

The time taken is inversely proportional to the speed of the processor and proportional to the square of the image diameter.

Image load time

If the default or external images are used to create the globe picture, there may be a noticeable pause before the globe is first seen while the images are first loaded and decompressed. For a faster initial display, set both daylight and night images to use the ‘Classic’ imagery, which has a negligible load time.
[previous | contents | next]
Copyright (c) IBM Corporation, 2009. All rights reserved. ©
Author: Mike Cowlishaw,