Point definition

Many functions inside GiD need points to be defined by the user. Points are the lowest level of geometrical entity and therefore the most commonly used. Consequently, it is important that you have a thorough understanding of how to do this. Sometimes an existing point is required and sometimes a new point must be defined.

Window for entering coordinates

All the options explained in this section are available through the window shown above (see Coordinates window ). This window is accessed via the pull-down menu Utilities -> Tools. Here you can choose not only the kind of reference system - cartesian, cylindrical or spherical - but also whether to use a global or local coordinate system and whether the origin of coordinates is fixed or relative (where new coordinates are relative to the last origin point entered).

In general you can enter points in the following ways:

  1. Picking in the graphical window.
  1. Entering points by coordinates.
  1. Selecting an existing point.
  1. Using the Base button.

Picking in the graphical window

Points are picked in the graphical window in the plane z=0 according to the coordinates viewed in the window. Depending on the activated preferences (see Preferences ), if you select a region located in the vicinity of an existing point, GiD asks whether it should create a new point or use the existing one.

Entering points by coordinates

GiD offers a window for entering points in order to create geometries easily, defining fixed or relative coordinates as well as different reference systems - cartesian, cylindrical or spherical.

The coordinates of a point can be entered either in the enter points window or in the command line by following one of two possible formats:

  1. The format: x,y,z
  1. The format: x y z

Coordinate z can be omitted in both cases.

The following are valid examples of point definitions:

5.2,1.0 5.2,1

8 9 2 8 9,2

All of a point's coordinates can be entered as local or global and through different reference systems in addition to the cartesian one.

  1. Local/global coordinates
  1. Cylindrical coordinates
  1. Spherical coordinates

Local/global coordinates

Local coordinates are always considered relative to the last point that was used, created or selected. The Utilities -> Id command allows you to make a reference to one point (see Id ). Then, to define points using local coordinates referring to the same point, use Options and Fixed Relative when entering each point. The last point selected or created before using this will be the origin of the local coordinate system. It is also possible to enter this central point by its coordinates.

The following are valid examples of defining points using local coordinates:

Example (1):

1,0,0

@2,1,0 (actual coordinates 3,1,0)

@0,3,0 (actual coordinates 3,4,0)

2,2,2

@1,0,3 (actual coordinates 3,2,5)

Example (2):

1,0,0

Fixed Relative (when creating the point)

@2,1,0 (actual coordinates 3,1,0)

@0,3,0 (actual coordinates 1,3,0)

2,2,2

@1,0,3 (actual coordinates 2,0,3)

Example (3):

'local_axes_name'2.3,-4.5,0.0

The last example shows how to enter a point from a local coordinate system called 'local_axes_name' (any name inside the quotation marks will work), previously defined via the option define local axes (see Local axes ).

All the examples have been presented using a cartesian notation. However, cylindrical or spherical coordinates can also be used.

Cylindrical coordinates

Cylindrical coordinates can be entered as: r<angle,z

The z_coordinate may be omitted and angles are defined in degrees. Cylindrical coordinates can be applied to global and local coordinate systems.

The following are valid examples of the same point definitions:

example (1):

1,0,0

1.931852<15

example (2):

1,0,0

@1.0<30

Spherical coordinates

Spherical coordinates can be entered as r<anglexy<anglez

Anglez may be omitted and angles are defined in degrees. Spherical coordinates can be applied to global and local coordinate systems.

The following are valid examples of the same point definitions:

Example (1):

1,0,0

1.73205<18.43495<24.09484

Example (2):

1,0,0

@1.0<45<45

Base

If the Base button is selected (it is set by default to No Base), a point can be retrieved from any of the other modes. Then, the coordinates of this point, instead of being used immediately, are written in the command line and can be edited before they are confirmed.

It is possible to change the way that GiD works with points by default via preferences (see Preferences ).

Selecting an existing point

When using a function that asks for a point, e.g. line creation, GiD will expect you either to enter a new point (the cursor is a cross) or select an existing one (the cursor is a box). To change from the first mode to the second, click the Join button in the Right buttons menu or the Contextual mouse menu, or use the shortcut (Ctrl-a); the option will then change to No Join. Simply select an existing point to pick it. (Ctrl-a) switches from Join to No Join and vice versa.

The special options FJoin and FNoJoin force GiD to change either to Join mode or No Join mode independently of the previous mode.

Point in line

With this option selected, when creating a new point or line, etc., you can only select points that lie on existing lines. To switch it off, simply select No Point in line.

Point in surface

With this option selected, when creating a new point or line, etc., you can only select points that lie on existing surfaces. To switch it off, simply select No Point in surface.

Tangent in line

Using this option, you can pick over a line in the graphical window. A vector will be returned that is the tangent to the line at the point you have picked.

Normal in surface

Using this option, you can pick over a surface in the graphical window. A vector will be returned that is the normal to the surface at the point you have picked.

Arc center

Using this option, you can left-click on an arc in the graphical window and a point will be created at its center.

Grid

It is possible to use an auxiliary grid of lines to define 2D points easily. The 'snap' function can be activated to force points to grid intersections.

From the preferences window (see Preferences ) it is possible to set the separation between lines and to show the origin, extents, etc. of the coordinates.

There is a small button in the bottom right-hand corner that activates or deactivates the grid and 'snap' functions.