terminology question: what is a "normal map"?

[Liar]

Hey all,

Stupid question, i am sure:

I had thought that "normal map" meant, an image file that just 'maps' directly onto a spherical object, as opposed to a specular map, cloud map, night map, or an image file that maps onto a non-spherical custom-designed object like a spacecraft or a non-spherical asteroid.

But browsing the Jupiter section of the Add-Ons site (http://www.celestiamotherlode.net/catalog/jupiter.php), I noticed that there are some files that fit this definition that are not labeled as "normal maps"; eg: John Van Vliet provides a Callisto Virtual Texture, called 'Callisto 16K VT' (described as "16K Callisto Surface Virtual Textures"), but he *also* provides a 'Callisto (8K VT) Normal Map' (described as "Normal virtual texture - Artists concept -").

Is the 8K one called a Normal Map to distinguish it from the 16K one? If so, then does Normal Map have a different, more technical meaning than I thought?

Further down the page, there is an 8K Ganymede file called "8K Ganymede Surface Texture", and then, just below it, an 8K Ganymede file called "8K Ganymede Normal Map Texture."

I had thought that "surface texture" and "normal map" meant the same thing... what distinguishes them?

[Liar]

I should mention, by the way, i did look through the "Some informations about textures (little FAQ)" FAQ at the top of the board, and found this exchange:

what is the difference between a normalmap and a standard texture

http://members.shaw.ca/jimht03/normal.html

Bye Jens

...but (as you'll see if you follow the link) the link no longer leads to an explanation of the difference between standard textures and normal maps in Celestia (although there is a tutorial on that site which does explain the concept of a "normal map" in the history of 3D game development, i can't match this up with my knowledge of Celestia, or see what the difference is with a "standard texture" in Celestia).

[Adirondack]

Liar,

Wikipedia is your friend: http://en.wikipedia.org/wiki/Normal_mapping

Adirondack

[CAP-Team]

A normal map is a specific type of map, there are several types:

texture (surface map): like a map of the world
cloud map: just the clouds
bump map: a black-and-white height map, where black is level 0 and white is the heighest point in the map
normal map: a special type of bump map. This map does not use shades of gray but colours (x y z values) to specify a direction (the normal) on a map.

Normal maps and bump maps can be applied on a planet or moon so craters are rendered with appropriate shades and depths, it has nothing to do with being "normal".

[Liar]

Ahhhh, thank-you

[LordFerret]

Excellent. I'd been quite confused about that myself.