the eye of the storm

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world builder options

Seed

The Seed is the value used as the starting point for the random number series used to the generate the world. Each seed will produce a different world, though seeds which vary by very small amounts (changing the 10th and/or 11th fractional digit is usually best) will only differ slightly. This can be a good way to 'tweak' your world if it is close to what you want, but not quite right.

Initial Altitude

The program generates planet maps based on recursive spatial subdivision of a tetrahedron containing the globe. The Initial Altitude option specifies the initial altitude of the corners before subdivison. Increasing this will increase the amount of land on the planet and vice-versa. The default value is -0.02, which gives a slight preference for water. Changing this value by +/- 0.01 will change the water percentage by 5-15% (depending on the planet in question).

Distance Variation and Altitude Variation

The Distance Variation and Altitude Variation options control the contribution of distance and altitude difference to altitude variation. The higher these numbers are, the more ragged your landscape will be. The Distance Variation controls how much altitude changes by distance and the Altitude Variation controls how much the steepness of terrain affects roughness. The idea is that level terrain tends to be less rugged than sloping terrain. You shoudln't let these vary by more than a factor of 2 from the default values.

Width and Height

Specifies the dimensions of the picture, in pixels. Larger pictures obviously take longer to generate.

Latitude and Longitude

Specifies the centre point of the map.

Zoom

Specifies the magnification. Larger numbers zoom in to show smaller areas of the world.

Outline

Produces a black and white outline map. Very useful if you want to print out the map.

Black Borders

Outlines the land areas with a black border.

Bumpmap

The Bumpmap option activates bumpmap shading. This shades the colour depending on the angle (which is not currently editable), creating more 3-dimensional looking maps.

Grid

This displays a latitude and longitude grid on the map, at degree intervals specified by the latitude and longitude values.

Projections

The Mercator, Peters and square projections project the globe onto a cylinder wrapped around the equator of the globe. The cylinder is then unfolded to give a flat map. Hence, lines of equal longitude or latitude map to vertical or horisontal lines respectively.

The Mercator projection preserves angles (it is a conformal mapping) and compass directions but distorts area quite heavily towards the poles. The map extends infinitely north/south.

The Peters projection project a point horisontally out to the cylinder (which is afterwards strected by a factor of 2). It preserves relative area, but not angles or compass directions (expect for directly east, west, north or south). Areas near the equator will appear stretched up/down (by a factor of 2 at the equator) whereas areas near the poles are flattened. At latitude 45, areas have approximately the right proportions.

The square projection projects latitudes equidistantly. This projection preserves neither area nor angles, but it preserves distances in the vertical direction.

The Mollweide projection maps the earth to an ellipse. It preserves area. It is mainly used for world-maps and is best viewed with the Grid option, as longitudes are strongly distorted. If the Mollweide projection is used, the Longitude option is ignored, only equator-centered maps are made.

The sinusoidal projection maps the globe onto 12 sinusoidal "slices". The projection preserves area as well as distance from equator. A globe can be made from this projection by folding the map into a cylinder and bending the slice tops/bottoms inwards.

Mercator, Peters, square, Mollweide and sinusoidal maps at magnification 1 are scaled to fit the Width. Except for the Mercator projection, a full world map is twice as wide as it is high.

Assuming an Earth-sized planet of circumference 40000km we can relate this to scaling factors. To find the equatorial scaling factor, divide 4x10^9 by the width of the map (in centimeters) and then by the magnification factor. Hence, a map of width 20cm at magnification 2 has a scale of 1:1x10^8 at equator. For the Mercator projection, the scale at latitude L is 1/cos(L) times the equatorial scale. Hence, a map of width 20cm and magnification 2 has scale 1:1.416x10^8 at latitude 45 and scale 1:2x10^8 at latitude 60.

A number of azimuthal projections are available. Azimuthal projections project the globe onto a plane that touches the globe at the specified longitude and latitude. Azimuthal projections are approximately accurate at the centre of the map, but distort areas away from this. The different azimuthal projections distort in different ways:

Stereographic projection projects a point on the surface by following a line that starts in the point on the globe opposite the point that touches the plane and goes through the point of interest, until this line hits the plane. It preserves angles (i.e. local shape) but neither area nor compass directions. The entire globe is mapped onto the infinite plane, so you can never get a full world map. The distortion will be very severe when more than a hemisphere is shown.

Orthographic projection projects at right angles to the plane. It preserves nothing of interest, but is what you would see if you view the planet from space (from infinite distance). It can never show more than a hemisphere (which is mapped to a circle).

Gnomonic projection projects along a line starting in the center of the globe. It has the property that great circles are mapped to straight lines, which makes it useful for navigating by sea or air. A hemisphere maps to the infinite plane, so it can never show all of a hemisphere and distortion gets heavy when you get more than 60 degrees away from the centre.

Area preserving azimuthal projection preserves relative areas, but not shapes or angles etc. It maps the entire globe onto a circle of a radius twice that of the globe, but distortion along the edges is severe.

The orthographic projections are scaled so the diameter of the planet at magnification 1 is the full Height of the picture. Stereographic, gnomonic and area preserving azimuthal projections use the same scale as orthographic in the center of the picture. To find the scaling factor (again assuming Earth-sized planets) at the centre of the picture, divide 1.273x10^9 by the height of the map (in centimeters) and the magnification factor. Hence, a map of height 20cm with magnification 2 will have a central scale of 1:3.18x10^7. This is independent of latitude. To obtain a scale of 1:S, multiply 1.273x10^9 by the height of the map (in cm) and divide by S to obtain the magnification factor to use with the program. To get, e.g., 1:10^7 on a map of height 20cm, use -m 2546. As the size of the map in cm depends on how many pixels per cm the output media uses, the program can not calculate actual scales.

The conical projection is a conformal (angle preserving) projection from the sphere onto a cone that touches the specified latitude. The cone is cut opposite the specified longitude and laid flat, so it appears like a pie section. For latitudes close to 0 or 90, this approaches the Mercator and stereographic projections (respectively). If the extremes are specified, these will be used instead of the conical projection. The scale at the center of the map is the same as for ortographic and stereographic projections. This projection is good for mapping areas that have large east-west extent and are not close to the equator (e.g. Russia). Using conical projection, all of the planet is mapped onto a finite section of a cone, so you can make complete world maps. It is, however, not really suited for this, as latitudes far away from the specified latitude are very distorted.

Regardless of the projection used, maps that show only small sections of the planet will have little distortion and the scale will differ very little across the map.