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GEOD

point

The point command is the most basic geometric primitive used by GEOD, although it is rarely used on its own.

In practice, points are mainly used as markers, for example to follow the evolution of a point attached to a curve during an animation, or as control points for constructing other curves.

Summary

Construction: position, range, and slope

In GEOD, a point is defined not only by its coordinates x and y, but also by its slope and its range.

Example:

  point x 125 y 50
      slope 35
      range 30

Figure 1: The point command.

The first line defines a point with coordinates x = 125 and y = 50. GEOD follows the usual coordinate conventions: the x axis runs from left to right, and the y axis runs upward. These two coordinates are mandatory arguments of the point command.

The following lines are optional and define additional geometric properties.

The subcommand slope specifies the dip, that is, the angle between the horizontal and the right-hand branch drawn by the point. This angle is measured in degrees, clockwise.

A value between 0 and 90 draws a branch dipping to the right, whereas a value between -90 and 0 draws a branch dipping to the left.

The subcommand range specifies the range, that is, the length of each arm of the point. For example, a range of 30 makes GEOD draw a line 60 units long, centered on the point.

The meaning of the range is not always immediately obvious. It is especially useful when defining the shape of Bézier curves. In practice, the range represents the approximate domain over which a locally measured dip remains valid.

Figure 2: Setting the dip of a point with slope.

It is also possible to define asymmetric points, with different slopes and ranges on the left and right sides, using leftslope, rightslope, leftrange, and rightrange.

  point 100 200
      range 40
      leftslope 45
      rightslope 0

Note that leftslope follows the opposite convention from slope and rightslope. For a positive value on the left side, GEOD draws a half-line dipping to the left, and vice versa.

In the example above, the abbreviated syntax without the keywords x and y is used to define the point coordinates.

Figure 3: Left and right dips with leftslope and rightslope.

With leftrange and rightrange, the lengths of the left and right arms can be adjusted independently.

  point 100 200
      leftrange 20
      rightrange 40
      leftslope 45
      rightslope 0

Figure 4: Left and right ranges with leftrange and rightrange.

Graphic attributes: colors and symbols

The appearance of a point can be customized with subcommands such as color, size, markerscale, width, filled, and others described below.

Change the color with color

The subcommand color changes the display color of the point symbol.

  color blue

This sets the symbol color to blue.

The color names recognized by GEOD are:

A more precise color can also be specified numerically:

  color 0.9 0.1 0.2

In this case, the three numbers are the red, green, and blue components. Each value must lie between 0 and 1.

Change the size with size

The subcommand size sets the display dimensions of the symbol.

  size 10

This draws a marker within a square area 10 units wide and 10 units high.

Change the size with markerscale

The subcommand markerscale provides an alternative to size. It takes a single argument corresponding to a scale factor. A value greater than 1 enlarges the symbol, whereas a value smaller than 1 reduces it.

  markerscale 2

This multiplies by 2 the dimensions previously defined by size.

Choose the display symbol

By default, GEOD draws a square 10 pixels wide. Other symbols can be selected with the following subcommands:

Figure 5: Choosing the display symbol of a point.

The subcommand plane is used to display a dip symbol. Without an argument, it shows a horizontal dip symbol, that is, a simple cross. To specify a dip of 30 degrees, write:

  plane 30

The azimuth of the dip symbol is controlled by slope, and the length of the azimuth bar by range. Note that size and markerscale do not affect this type of marker. Use range instead. The length of the small bar representing the line of greatest slope depends on the dip value.

Figure 6: Displaying a dip symbol with plane.

To use a character as a marker, use char followed by the desired character. The character is automatically centered on the point.

  char U

Figure 7: Using a character as a display symbol with char.

Convert open symbols into filled symbols with filled

The subcommand filled turns an open marker into a filled one.

The instruction

  square

draws an open square, whereas

  square filled

draws a filled square.

Set line thickness with width

The subcommand width changes the line thickness of the symbol.

  width 2

This draws the symbol with a line thickness of 2 pixels.

Hide a point with hidden

The subcommand hidden disables the display of the point.

  hidden

Invisible points can be useful as support points for other curves. For example, to define the subsidence movement of a compartment adjacent to a listric fault, two invisible points may be used, one as a pivot and the other as a guide sliding along the fault plane.

Use lharpoon and rharpoon to represent sinistral or dextral movement

The point command can also insert double arrows to indicate the relative motion along a fault by using lharpoon and rharpoon.

  point ...
      lharpoon

This draws two joined arrows indicating a sinistral movement.

To indicate a dextral movement, use rharpoon.

The spacing between the two arrows can be adjusted with size:

  point ...
      lharpoon
      size 10

This inserts arrows spaced 10 pixels apart.

The arrow length can be changed with range.

Figure 8: The lharpoon and rharpoon subcommands used to indicate relative fault movement.

Display an image with icon

The point command can also display an image with the subcommand icon, using the following syntax:

  point ...
      icon "filename"

Here, filename must be replaced by the name of the graphic file containing the image. Common formats such as PDF, Photoshop, PNG, and JPEG are recognized. The image is centered on the point.

The image file should normally be stored in the same folder as the script currently being edited. In some cases, it may be necessary to save the script first so that GEOD can locate the file correctly.

Images stored in other folders can also be used, either with a relative path:

  point ...
      icon "../icons/sedim/s0.pdf"

or with an absolute path:

  point ...
      icon "/Documents/icons/sedim/s0.pdf"

Figure 9: The icon "..." instruction for displaying an image.

The size of the image can be modified with markerscale. The image can also be rotated using slope.

The icon subcommand is best reserved for small images such as icons. For larger images, use the image command instead. If the same image must be repeated several times, it is better to use fill, which is more suitable for repeated icons.

The name subcommand

The subcommand name is used to assign a name to a point.

  name p0

This subcommand is very general. It is not limited to points and can also be used for other lines or objects in a cross-section. It is mainly used to associate graphical objects with one another.

Attaching a point to a curve

A point can be attached to a curve. It can then be used as a marker or reference point on that curve. For this functionality, see the corresponding section in the line command documentation.