I was researching alternative methods of data display and I ran across a bunch of programs that claim to display information in 2 and 1/2 dimensions. Needless to say, I was rather confused…what the heck is the 1/2 dimension??
Did you ever play Doom? You remember how even though everything looked 3D, you couldn’t have two objects in the same location at different heights? That’s the most likely meaning of 2.5D in this context.
The other possibility is that they’re using some kind of weird fractal method. Can you provide a link?
I think ultrafilter’s first idea is correct. IIRC fractal dimensions are usually some oddball number (like 2.61 or 2.488) rather than a nice round 2.5.
This is probably totally wrong, but what I imagined when I read the title was an environment like ours, but one of the spacial dimentions only permitted movement in one direction (how, I dont know, but it’d be kinda coolio).
Well, fortunately, we dont deal with different numbers of dimentions at A-level physics, or I’d have failed based on that.
Cheers, Harry
The 1/2 dimension is better than 2D, but not “true” 3D. So just halfway between. It’s not a mathematical concept, just a programming term.
The advantage over real 3D is that the math is a lot easier. And the levels are simply maps + floor and ceiling elevations, which is easier to design than a true 3D environment.
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- If a game was in 2.5-D. what that -usually- meant was that the walls were true 3-D generated, but the characters and other objects were really only 2-D sprites scaled up and down to show proper distance perspective.
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- For a statistical or mathematical program, heck I dunno, could mean anything. What type of program are you referring to?
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Reminds me of games like Pandemonium! and Klonoa.
I suppose we inhabit a 3.5D universe: Three full dimensions with one that only allows movement one way. That half dimension is time, of course.
I’m guessing that’s the correct idea - a 3D graph where negative numbers are not allowed on one of the axes (so you have a “floor” bounded by an origin plane).
On further reflection, and some Google checking, I think 2.5D in charting refers to something different than it does in first person shooters. It’s where a 2D bar chart (or a line chart) is made to look 3D by drawing diagonal lines back from all the points, making it look kinda three dimension. Like this.
Actually, ultrafilter and SmackFu are correct when it comes to game graphics, DougC. A 2.5D game engine does not use a true 3D environment with sprites. I think a lot of people have this misconception because the sprites are the most obvious visual problem in Doom, and Doom is the classic example of a 2.5D engine. So people say, “oh yeah, I remember what Doom looked like – that’s 2.5D” and they’re thinking specifically of the sprites. But using sprites does not make a 3D game 2.5D (Descent and Quake 1 both used sprites in a real 3D world, although Quake’s use of them was slightly more sophisticated). Given an environment which can be represented by 2.5D, a layman would actually be hard-pressed to tell the difference between a 2.5D engine and a 3D engine rendering of that world.
Whether or not the OP was referring to that particular meaning of “2.5D graphics” is another question.
I think SmackFu’s got it; that makes a lot more sense regarding data interpretation than do Raytrace engines. 
This is pretty interesting stuff though - I think I get the general point of what you’re saying about Doom, Quake, etc… but is there a website that has more extensive/technical information about 2.5D games?
It’s usually referred to as “raycasting”. A google search on that will reveal lots of info on it.