ARM Club 3/TheARMClub_PDCD3.iso/hensa/graphics/fractal_1/!Fractal/Help/Faults

Text File | 1996-10-09 | 7KB | 141 lines

Fault
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Generates a landscape by a very simple simulation of geological faulting,
showing the result as a contour map. Each time a fault occurs, a part of the
landscape is moved up (or down). By repeating the process hundreds or
thousands of times at random locations across the image, an uneven terrain
is created. The portion of the terrain faulted is determined by the fault
type selected by Fault->Type. All but Linear are based on shapes, where the
region within the shape is faulted upwards or downwards. The position of the
fault shape is chosen at random.

For Linear faulting, a line is chosen at random across the image, then one
side is faulted downwards or upwards. The initial image is at a set level
to accomodate downward faults. Linear faults look best when plotted in 3d
rather than as a contour map.

The data parameters are:

No. Faults: the number of faults to be run before stopping. Higher numbers
produce more realistic and uneven shapes.

Shape Size: The size of the fault shape in OS units. Larger sizes tend to
produce more generalised faults but may lead to obvious boundary lines which
can look unrealistic. Smaller shapes give more uneven, bumpy landscapes.
Sizes of 1/5th the total image give a good balance between smoothness and
variety. Larger shapes will take longer to plot. Not used for Linear faults.
The size is limited by memory.

Step: The maximum height increment for each fault. The maximum height that
can result is 255 unless Fault->Wrap is turned on in which case heights wrap
around to 0. For 3d shapes such as Cone and sprites, the Step represents the
maximum height (usually the centre).

Base Level: A value 0-255. For Linear faults or when using Up/Down faulting,
this sets the initial level (128=middle). Change this value to alter the
"sea level" or bias towards low or high levels.

Seed: The random number used as a seed to generate the landscape. To
recreate a landscape, set Fault->Random off and set the seed value. This
allows the effects of different shapes, sizes and step values to be
evaluated.

From the Fault menu the following options are selectable:
Type: leads to a submenu showing the type of fault to use. The first set are
shapes, the size of which is set from the data value Shape Size, and maximum
height by Step.
  Circle    : a circle of radius Shape Size/2.
  Cone      : a conic rising evenly in height (max Step) to the centre.
  Hexagon   : a hexagon of radius Size/2.
  Octagon   : an octagon of radius Size/2.
  Octagon 3d: a 3d octagon rising in height to the centre.
  Sprites   : leads to a panel listing a sprite shape to be used as the
              fault pattern. Click on Sprite to use this feature, and click
              on the name of the sprite to use.
  Linear    : Uses linear faulting rather than by shape. When Random Step is
              on, the Step size is the maximum, rather than the actual amount.

Random: when on generates a random landscape. Turn off to recreate a
landscape using the Seed value.

Wrap: when on allows height values to wrap around from 255 to 0, otherwise
values peak at 255.

Up/Down: when on faults are made randomly upwards or downwards, otherwise
only upwards faults are made. When off, using a lot of faults will cause the
image to end up as all high, so setting this on will help to keep heights
between 0 and 255. Linear faults are always made in Up/Down mode.

Using Sprite Fault Shapes
-------------------------
Any shape can be used as the fault pattern. The colour values of the sprite
are used as the relative fault height, whilst the overall size of the sprite
is set by Shape Size as for other shapes. The supplied sprites are in the
file FaultSpr (see Misc->Resources).

You can experiment with your own shapes by dragging a sprite file onto any
of !Fractal's windows whilst Fault is selected. The sprites must be defined
in a 256 colour mode - 13 and 21 are best since the pixels are square. Each
sprite should be square in terms of OS units, but the pattern inside can be
any shape.

It is best to draw the pattern in distinct colours since the low colour
values are difficult to see. Treat each colour number as a relative height
value. At plot time the maximum colour is set to the value of Step and the
other colours are scaled accordingly. Circular patterns tend to give the
most realistic landscape effect, but feel free to experiment since strange
patterns can be produced with linear shapes. You can think of Fault as a
special type of Tiling mechanism.

Hints And Tips
--------------
Faulting with shapes works best with a thousand or more faults with a shape
size of 100-200. With 3d shapes use a higher step than normal. With Linear
faulting try 400 faults with a step value of 8. With Random Step off, each
fault is of the same size. Linear faults look better once transformed into
3d, since this removes some of the linear effect.

The resulting image looks best with the Landscape display palette. If the
image is too low you'll just see blue, so use the Palette adjust facility
(striped Tool icon) to alter the mapping until you get a mixture of sea and
land. Alternatively load your own customised palette made with !EditPal. For
instance, a palette of various shades of white, grey and light blue give a
very realistic cloud effect.

To view the landscape in 3d try 3d_View or Render using either a Log or
Linear 3d mapping (in the 3d panel). Use the 3d Scalar value to accentuate
or smooth the image. Again, select the Landscape palette. Try the Riemann
plot to create your own globe.

Try composite faults by turning off Image->Redraw->Clear. This allows
different shapes, sizes and step values to be cumulatively applied. When
creating composite images it is best to start with a large shape size,
running for several hundred faults, to generate the basic rolling terrain.
Then use a smaller fault size, increase the number of faults and step size
to give more localised variation and peakiness. The best shapes are the Cone
and Octagon 3d - for these you'll need a relatively larger size than Circle
because of the gradual rise in height. Try mixing shapes to create different
effects - eg. start off with Linear, then switch to cone to smooth the
image. Using large shape sizes can also produce interesting patterns.

Faulting by shape is a variation on tiling, and many images can be created
by using the function in this manner rather than for landscape generation.
Try colour cycling (especially with a single colour) with an image created
with a few faults and large shape size.

Scripts
-------
Use !Fractal's script facility to create images from composite faults. See
the Misc->Resources directory for sample scripts. This is a very powerful
facility which allows complex patterns to be created.

Algorithm
---------
Faulting by shape simply involves selecting a point at random and then
plotting the shape centred on that spot. The value of each shape pixel is
added to the image pixel value - if Fault->Wrap is off, then the maximum
value of 255 is set, otherwise the value wraps around.

With Linear faulting, two co-ordinates on 2 different sides are chosen at
random. One side is faulted down or up (both chosen at random). If the
height is <0 or >255 then it is wrapped inwards.