Terranova: Planet Maker

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    Image size:    Mesh: 

Fractal dimension
Power spectrum
Icecap level
Glacier level
Fractal dimension
Power spectrum
Colour saturation
Cluster Density Min
Cluster Density Max
Cluster Diameter Min
Cluster Diameter Max


Below the “Generate” button is a control panel you can use to customise the images produced. At the left is a drop-down list which lets you chose images of planets, cloudy skies, or star fields. If “Random” is checked, the parameters for each image will be picked at random and those used will be displayed in the sliders and numeric fields below. If “Random” is unchecked, the sliders are activated and may be used to set the image generation parameters as described below. You can choose the image size between 256 and 2048 pixels and, in addition, a “Full Screen” option which creates an image as large as the screen on which the browser is running; use this to make “wallpaper” images for your computer.

Planet and cloud images are synthesised by generating a Gaussian random spatial frequency map which is transformed into a table of elevations with an inverse Fourier transform. The “Mesh” drop-down box specifies the size of this array, or mesh. Larger arrays permit higher spatial frequencies and elevation resolution and thus produce images with more detail when the Fractal dimension (see below) is large. However, the computation time and memory required to generate an image increase as the square of the mesh size, so smaller mesh sizes are preferable for slower computers.

The detailed parameters used to generate images are displayed in the sliders and numeric fields in the box at the bottom of the control panel. When “Random” is checked, the box is shown with a grey background and the controls are disabled: values for each image will be chosen randomly between the limits in the “Default” column and shown in the controls. Unchecking “Random” activates the controls, which you may use to set the following parameters.

Parameter Default Limit Description
Min. Max. Min. Max.
Fractal dimension 2.0 2.7 1.0 3.0 Controls the roughness, or scale of detail in the terrain for planets or for clouds in the sky. Lower values produce smoother results, while high values may be close to completely chaotic. Different ranges of fractal dimension can be specified separately for planet and cloud images.
Power spectrum 1.0 1.5 0.1 4.0 Sets the “power spectrum” (or exponent) used to scale values representing terrain elevation (for planets) or density (for clouds). The result of the image synthesis is an array of elevation values between 0 and 1. A non-unity power factor exponentiates each of these elevations to the specified power. For example, a power factor of 2 squares each value, while a power factor of 0.5 replaces each with its square root. (Note that exponentiating values between 0 and 1 yields values that remain within that range.) Power factors less than 1 emphasise large-scale elevation changes at the expense of small variations. Power factors greater than 1 increase the roughness of the terrain and, like high fractal dimensions, may require a larger Mesh and/or image size to look good. Again, you can set the power factor independently for planet and cloud images.
Icecap level 0.2 0.6 0.0 1.0 Sets the extent of the polar ice caps. The default range produces ice caps similar to those of the Earth, varying from ice age to interglacial periods. Smaller values reduce the amount of ice, while larger settings create more prominent ice caps. Sufficiently large values, in conjunction with small settings for Glacier Level (try 0.1) create “ice balls” like Callisto and Europa.
Glacier level 0.6 0.85 0.0 1.0 This item controls the extent to which terrain elevation causes ice to appear at lower latitudes. The default value range makes the polar caps extend toward the equator across high terrain and forms glaciers in the highest mountains, as on Earth. Higher values make ice sheets that cover more and more of the land surface, simulating planets in the midst of an extreme ice age. Lower values tend to be boring, resulting in unrealistic geometrically-precise ice cap boundaries.
Star Density 50 75 0 1000 In planet and star field images, field stars are placed randomly with a density given by this item. The probability a star will be placed on a given pixel is the value of this item divided by 1000.
Star Colour Saturation 100 150 0 1000 Controls the degree of colour saturation of stars in planet and star field images. The default values yield stars which resemble the sky as seen by the human eye from Earth's surface. Stars are dim; only the brightest activate the cones in the human retina, causing colour to be perceived. Higher values approximate the appearance of stars from Earth orbit, where better dark adaptation, absence of skyglow, and the concentration of light from a given star onto a smaller area of the retina thanks to the lack of atmospheric turbulence enhances the perception of colour. Values greater than 250 create “science fiction” skies which, while pretty, don't occur in this universe.
Star Sharpness 1.4 0.3 1.5 Stars are, of course, point sources of light, but it's common in star charts to represent their intensity by size, as they appear on a photographic plate. Planet Maker draws stars with a Gaussian point spread function whose maximum intensity depends upon the magnitude of the star. The greater the sharpness, the more stars will be point-like. Reducing the sharpness will cause the star images to spread out, looking more like a photographic image of the night sky.
Star Brightness 1.0 0 5 There are many more dim stars than bright ones, and this distribution is respected when plotting star fields. You can scale the brightness of the stars by adjusting the brightness control. Increasing the brightness will make more stars visible, while reducing will result in sparser star fields.
Star Gamma 1.9 0.5 2.5 The contrast between dim and bright stars is adjusted by gamma correction, using the exponent set by this control. Lower values reduce the contrast among stars, while higher values enhance it.
Star Clusters -3 1 -10000 10 In addition to “field stars” governed by the Star Density parameter, up to ten star clusters may appear at random positions in star field and planet images. The number of clusters in a given image is chosen randomly based upon this item. Negative values are equivalent to zero, permitting you to configure star clusters to appear only in a given fraction of images.
Star Cluster Density 10 100 0 500 The density (enhancement of star placement probability) at the centre of a star cluster is chosen between the limits given by this item. Larger values result in dense globular clusters like M13, while smaller values simulate open clusters. The density of each cluster is randomly chosen to be within the limits set by the minimum and maximum value.
Star Cluster Diameter 10 30 0 200 The diameter of star clusters is given by this item, as a percentage of the width or height of the image, whichever is smaller. The size of each cluster is randomly chosen to be within the limits set by the minimum and maximum value.

Images produced by Terranova: Planet Maker are in the public domain. They may be used in any manner without permission, restrictions, attribution, or compensation. Back links, or citations of the URL in print publications are appreciated, but are not a condition of use.

by John Walker
June 2017