Map Mapping and Other Questions.

Map Mapping and Other Questions.

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Sat Feb 7 21:43:15 2015   by   Vespero.
Hello!

I'm looking to use planet for various projects of mine (writing and roleplaying) and I was wondering if you guys could help me with a few things.

Firstly, is there any good way to turn one of these 2D projections into a 3D material? Not necessarily topographically, I'm chiefly looking for a way to map one of these maps to a sphere to more realistically view the projections.

Secondly, when generating a projection, the dimensions of the resulting file can be specified. Does altering these numbers squash/stretch the file, or generate further past the borders?

Thirdly, since I'm not nearly as versed in cartography as I would like, what is the best way to determine scale on the projection? Can the latitude/longitude grid be used to determine distance in a reliable way? (on a reasonable scale for working with.

Fourthly, "Contour Lines" is an option, but what do the numbers refer to?

Thanks for the help (love the generator),
Vespero.
 
Mon Feb 9 12:32:21 2015   by   Torben
The maps are actually generated in 3D coordinates which are then mapped to 2D using various projections, but there is currently no interface for getting the 3D coordinates.  You can map any projection back to a sphere by using the inverse projection.  The easiest is probably the square projection where x and y coordinates are directly proportional to longitude and latitude, so you just need to convert longitude/latitude pairs to (x,y,z).

The scale is determined in part by the size of the image and in part by the zoom factor.  Some projections (Mollweide, Mercator, square, Peters, icosahedral and sinusiodal) scale so, at zoom = 1, the equator maps to the width of the image.  Orthographic scales so the north pole is at the top of the image and the south pole is at the bottom.  The other azimuthal projections (area preserving, stereographic and gnomonic) use the same scale as orthographic at the center of the image, but distort scale differently.  More details in the manual at http://www.diku.dk/hjemmesider/ansatte/torbenm/Planet/ .  The zoom factor is a straight-forward multiplier for the scale.

No projection preserves distances (except in specific directions), so you can not measure distances directly on the map.  If you know the longitude/latitude pairs of two points you can calculate their distance using the formula at http://www.movable-type.co.uk/scripts/latlong.html (note that this uses Earth radius as scale).  Again, the square projection makes it easy to find longitude and latitude directly from the image coordinates.

With contour lines, the number is the spacing between contour lines in terms of latitude.  Since there is no a priori altitude scale, this is specified in the number of steps in the colour map.  So using a colour map with 256 different colours will give different contour lines than a colour map with 32768 colours.  This is, admittedly, rather crude.
 
Mon Feb 9 15:48:56 2015   by   Ron Vantreese

> Firstly, is there any good way to turn one of these 2D projections into a 3D material? Not necessarily topographically, I'm chiefly looking for a way to map one of these maps to a sphere to more realistically view the projections.

I use POV-Ray (www.povray.org) and I take a square projection and wrap it around a sphere object.

Here is a sample of POV-Ray code:
#macro Land(radius, albedo, landmapimagetype, landmap)
sphere
{
<0, 0, 0>, (radius*unitscale)
texture
{
pigment
{
imagemap
{
mapimage(landmapimagetype, landmap)
maptype 1
}
}
finish
{
ambient 0
brilliance landbrilliance
albedoeffect(albedo)
}
}
}
#end

... it takes time getting used to it, and you don't necessarily have to make it as complex as I did to wrap a planet map around a sphere.

The 3 minimum requirements in POV-Ray are Light, Camera, and at least 1 object.

 
Wed Feb 11 09:44:47 2015   by   RGT
The maps are good to be placed on spheres in a 3d modeling program, as the poles tend to be water or iced, so no weird issues there.

I use the Square projection and I get a good map I can use as a texture like in here: http://runetrantor.deviantart.com/art/Headquarters-Keeper-of-Galaxia-510976517

From what I have seen, there is no serious distortion of landmasses as it would if we used Mercator.
 

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