Create

This menu is for the generation of all the different possible geometrical entities. Usually, new entities are created inside the current layer (see Layers and groups (only Preprocessing)).
Geometry Menu>Create>Point
Menu: Geometry->Create->Point
Individual points are created by entering each point in the usual way (see Point definition). The points can then be joined together to form lines.
Caution: It is impossible to create new points joining old ones.
The Number option lets you choose the label that will be assigned to the next point created. If a point with this number already exists, the old line changes its number. This option is used for example to automatize thinks in macros, knowing the identifier of the entitiy because it is forced.
Geometry Menu>Create>Straight line
Menu: Geometry->Create->Straight line
Toolbar:
To create a straight line, start by entering just two points (see Point definition ), and then continue entering points in order to create more lines from the first one. Every part of the total line created is an independent line.
It is important to note that when creating lines, new points are also being created (if existing ones are not used).
The Close option joins the first point and the last point created with a straight line and finishes.
The Undo option undoes the creation of the last point (if new) and the last line. It is possible to continue undoing all the way back to the first point.
The Number option lets you choose the label that will be assigned to the next line created. If a line with this number already exists, the old line changes its number.
If Join is chosen, it is maintained for all points until No join is selected.
Geometry Menu>Create>NURBS line
Menu: Geometry->Create->NURBS line
Toolbar:
Interpolation / Fitting /ByControlPts
NURBS are non-uniform rational B-splines.
NUBS is a kind of polynomial piecewise curve, defined by a degree, a control polygon and a knot vector.
The degree is the polynomial degree.
The control points are a set of points that the curve approximates smoothly. Usually the curve pass through the first and last control point.
The knot vector is a vector of increasing real numbers (from 0 to 1 in GiD) that divides the parametric space in the intervals.
A NURBS (with 'R') could also have rational weights, an extra real value by control point. The curve approximate more closely the control points with bigger relative weight values. Rational NURBS are a quotient between two polynomials, this allow to mathematically describing conical curves like circumferences or ellipses in an exact way.
There are three ways of creating a NURBS line from series of points using this command:
Interpolation (default option): the NURBS will be a cubic polynomial calculating the control polygon and knots in such a way that the curve pass through all the user points.
Fitting: Similar to the interpolation case, but the curve will not exactly interpolates the user points, only approximate them by a 'minimum squared' criteria. The degree of the curve must be set before the curve calculation.
ByControlPts: Directly defines NURBS setting its degree and control polygon. The shape of the curve is similar to the control polygon, but it does not interpolate the polygon points.
During the session the selected method become the current one until it is changed again.
All the NURBS creation options are available from the contextual menu during the curve creation or from the Right buttons toolbar

The messages showed in the command line will orientate the user about the required parameters on each case.
When defining interpolating curves, you can choose to explicitly define the tangents to one or both ends (using the Tangents option). These tangents can be customized, in that they can either be defined by picking their direction on the screen or by considering an existing line as a tangent to the NURBS if it follows a previous curve (the option ByLine). The Next option allows only one tangent to be defined.
In this way, it is possible to create a closed NURBS by selecting the initial point as the end one and choosing one of the options 'Tangent', 'Next', or 'ByLine'.

The Undo option undoes the creation of the last point; this can be done all the way back to the first point.
When a NURBS has been created, all the interior points (except the first and last) are temporary points, not really entity points unless they previously existed.
To enter rational weights on the curve, the Edit NURBS line/surface command (see Edit NURBS) can be used.
Surface constant: This option allow the creation of a curve on a parametric surface setting the parameter u or v to a constant value specified by the user.
It is possible to create also NURBS curves from the Copy window, be extrusion of points with a transformation of translation or rotation, this allow the creation of straight lines and arcs respectively.


Geometry Menu>Create>Parametric line
Menu: Geometry->Create->Parametric line
Tool to create a parametric approximated curve

Parametric line window


The data that must be input are the mathematical formulae of the coordinates X(t), Y(t) and Z(t), where 't' is the parameter of the curve, and its value belongs to the interval [ t0-t1 ]. The curve is created by approximation and is a NURBS (Non-Uniform Rational B-Spline) which is created with N points. In GiD these kinds of curves are cubic (order 3).
The valid mathematical funcions are all Tcl functions:
+ - * / %
abs cosh log sqrt acos double log10 srand asin exp pow tan atan floor rand tanh atan2 fmod round ceil hypot sin cos int sinh
EXAMPLE
We fill the formula bars with the expression of a conic helix.
That helix starts with radius R₀=4 and finishes with radius R₁=1, performing N=3 turns from t=0.0 to t=1.0, the height also changes from 0 to H=5.

Example of a conic helix with a unique curve or with points only

Geometry Menu>Create>Polyline
Menu: Geometry->Create->Polyline
A polyline is a set of at least two other lines of any type (including polylines themselves). Every line must share one or two of its endpoints with the endpoints of other lines.
There are two possible ways to create a polyline, either by selecting one line and searching the rest until a corner or end is reached, or by selecting several lines (see Entity selection). In the case of the latter, the order of selection is not important but all of them must join each other by sharing common points.
Polylines are drawn in green to show the difference between the other lines, which are drawn in blue.
Polylines are widely used when creating 4-sided surfaces (see 4-sided surface creation) and automatic 4-sided surfaces (see Automatic 4-sided surface creation).
When deleting a polyline, all its lines are deleted. When exploding it (see Polyline), the polyline will disappear and its individual lines will appear.
It is not possible to create third level polylines: one former polyline can be included inside another, but this is the limit and these two cannot be included within a further polyline.
The Number option lets you choose the label that will be assigned to the next created line. If a line with this number already exists, its number is changed.

Geometry Menu>Create>Arc
Menu: Geometry->Create->Arc
Toolbar:
To create an arc you can either enter three points (By 3 points, see Point definition) or enter a radius and the two tangent lines at the arc's ends (Fillet curves).
It is important to note that when creating an arc, new points are also being created (if existing ones are not being used).
An arc that begins and ends at the same point (i.e. where the first and third points are the same) will be created as a circle. An arc will always include the second point that is entered, though this one is only used as a reference and, if it is not an existing point, is automatically erased when the arc is created.
The Undo option undoes the creation of the last point (if it is a new one). It is possible to continue undoing all the way back to the first point.
The Fillet curves option lets you input a radius and select two lines that share one common point. An arc will then be created and the two lines will be modified to be tangent and continuous with this new arc.
To convert one arc to another one with the same center and in the same plane but with a complementary angle, the Swap arc command can be used (see Swap arc).

Geometry Menu>Create>NURBS surface
Menu: Geometry->Create->NURBS surface
Toolbar:
NURBS are non-uniform rational B-splines. They are a type of surface that is defined by its control polygon (one set of points that the surface approximates smoothly), one set of knots for the two directions u and v (a non-decreasing list of real numbers between 0 and 1) and, optionally, one set of rational weights.
To draw the isoparametric lines in u,v=0.5, check the surface drawing type option in the preferences window.

• By contour: this creates a NURBS according to its contour lines. GiD automatically calculates the interior information of the surface so as to interpolate the boundaries smoothly. To create a NURBS surface, some lines must be selected (see Entity selection). The order of selection is not important but all of them must join each other by sharing common points and must form a closed contour. The number of lines must be equal to or greater than one and their shape must be topologically similar to a triangle or a quadrilateral in the space if the algorithm is to work correctly. This last argument is not necessary if all the lines lie in one plane. In this case, the surface is created as a trimmed one and any problems with the shape are avoided. It is possible to select the boundary lines and the boundary lines of interior holes at the same time, if all the lines belong to a plane.

Note: The No try planar option (found in the Contextual mouse menu) avoids the creation of a trimmed NURBS surface when lines are coplanar.
Note: To enter rational weights for the surface, use the Edit NURBS surface command (see Edit NURBS).

• Automatic: this automatically creates all possible surfaces with the number of sides given by the user. Every new surface will be created in the current layer.

Caution: When creating more than one surface in one go, it is possible that some undesired surfaces may also be created. It is necessary to check the surfaces after creation and erase the undesired ones.

• Trimmed: this option lets you select one existing NURBS surface and a set of closed lines that are inside the surface. Some of these lines may already belong to the contour of the existing surface. Some other lines may be created with an intersection with another surface. Another new surface will be created without changing the old one. It is possible to select the boundary lines and the boundary lines of interior holes at the same time, if all the lines belong to the surface:

Creation of a new trimmed surface with a hole

• Untrimmed: this constructs one new surface with the selected surface as its base and with the natural contours of the NURBS surface as its contours. The resulting surface is not trimmed.
• Parallel lines: this lets you create one surface given a set of parallel lines in the space. The new surface will interpolate all the selected lines.
• By points/By line points: these two options are available in the Contextual mouse menu after the NURBS surface creation tool is selected. By points creates a NURBS surface from a cloud of points, and By line points creates a NURBS surface from level curves. These two functions are very useful for creating relief and terrains. In the image below there is a NURBS surface created from level curves:

Note: This surface is an approximation to the selected points/lines, but there is no interpolation.

• Search: this lets you select one line and then creates one surface that contains that line.

Geometry Menu>Create>Parametric surface
Menu: Geometry->Create->Parametric surface
Tool to create a parametric approximated surface

The required input data are the mathematical formulae of the coordinates X(u,v), Y(u,v) and Z(u,v), where 'u' and 'v' are the parameters of the surface, and its value belongs to the intervals set in 'u in' and 'v in' respectively. The surface is created by approximation and is a NURBS (Non-Uniform Rational B-Spline), which is created with 'Number of points U' x 'Number of points V' points. In GiD these kinds of surfaces are cubic (order 3).
The valid mathematical funcions are all Tcl functions:
+ - * / %
abs cosh log sqrt acos double log10 srand asin exp pow tan atan floor rand tanh atan2 fmod round ceil hypot sin cos int sinh
Geometry Menu>Create>Surface mesh
Menu: Geometry->Create->Surface mesh
With this option a Surface mesh can be created by selecting triangular or quadrilateral mesh elements (see Surface mesh).
Geometry Menu>Create>Volume
Menu: Geometry->Create->Volume
Toolbar:
A volume is an entity formed by a closed set of surfaces that share the lines between them.
To create a volume, some surfaces must be selected (see Entity selection ) using the By contour option. The order of selection is not important but all of them must join each other by sharing common lines and they must form a closed contour.
If there is an error and the volume is not created, a window appears with some useful information.
The Search option lets you select one surface and create one of the volumes that contains this surface.
Volumes and their surfaces are automatically orientated so that they are meshed correctly.
An additional feature allows the selection of surfaces that form the outer part of the volume as well as the ones that form the holes at the same time. In this case, GiD automatically recognizes the holes.
The Automatic 6-sided volumes option creates all possible volumes that have 6 sides (contour surfaces). It can be applied several times over the geometry and volumes are not repeated. Every new volume will be created in the current layer.
This can be useful for structured meshing (see Structured_bad ).
Geometry Menu>Create>Contact
Menu: Geometry->Create->Contact
Contact surfaces and volume are pseud-geometric entities that act as a link between a pair of 'similar entities'
Both entities must be on the same 3D location, or in different locations (separated volumes) with a solid-rigid movement with some distortion.
More than a geometrical entity could be considered as a kind of meshing criteria, with master and slave nodes connected by elements (with zero jacobian if master and slave are on the same location)
These special entities are useful to simulate a contact of two domains.
Geometry Menu>Create>Contact>Surface
Menu: Geometry->Create->Contact surface
Contact surfaces are defined as being between two lines that are physically in the same place, but which have different line and point entities. From a contact surface, it is possible to generate contact elements, to be used by some calculation algorithms, which define a special contact between these two bodies.
Using contact surface entities is like a meshing specification. In this way, equal meshes will be generated for the two lines, ensuring a one-to-one relationship between nodes.
Choose the Contact surface option from the menu, and then select some lines on both bodies.
Contact elements are, by default, 4-node planar quadrilaterals. However, you can select 2-node lines for all cases (see Element type).
The 4-node planar quadrilaterals can be converted to the 8-node or 9-node for the quadratic case.
You can also select no mesh for the contact entity. This makes it possible to have exactly the same mesh for both lines but without any additional element between them.

Geometry Menu>Create>Contact>Automatic surfaces
A tool to automatically create contact surfaces between pairs of lines (of a selection) on the same location.
If the same contact surface exists it is not created again
Geometry Menu>Create>Contact>Volume
Menu: Geometry->Create->Contact volume
Contact volumes are defined between two surfaces that are physically in the same place but with different surfaces, lines and points. From a contact volume, it is possible to generate contact elements, to be used by some calculation algorithms, which define special contact between two bodies.
Those equivalent surfaces can be in the same location or can be separated by a movement (separated contact volume). The result will be equal meshes, ensuring a one-to-one relationship between nodes.
Choose 'contact volume' from the menu, and then select the surfaces. GiD automatically searches for possible contacts, combining the selected surfaces in pairs.
Contact elements are, by default, 8-node hexahedra or 6-node prisms (depending on the surface mesh).
However, you can select 2-node lines for all cases (see Element type).
The result elements can be also quadratic.
You can also select no mesh for the contact entity. This makes it possible to have exactly the same mesh for both surfaces but without any additional element between them.
When creating contact volumes, GiD internally checks what surfaces occupy the same location in the space and creates the contact, therefore there is no need to specify what surfaces have to be in contact. For this reason, several surfaces can be selected at once and GiD performs the contact automatically, indicating the number of contact volumes that have been generated.


Geometry Menu>Create>Contact>Separated volume
One feature of GiD is the option to create 'contact separated volumes' for surfaces that are not physically in contact.
For these separated volumes, GiD internally checks whether a unique solid-rigid movement exists between two surfaces and creates the contact. There is the possibility that multiple solid-rigid movements may exist. In this situation, GiD asks for the point image of a source point to define the movement and, consequently, applies the right contact.
Geometry Menu>Create>Contact>Automatic volumes
A tool to automatically create contact volumes between pairs of surfaces (of a selection) on the same location.
If the same contact volume exists it is not created again
Geometry Menu>Create>Geometry from mesh
Menu: Geometry->Create->Geometry from mesh
One node-one point
Creates a geometrical point for each node selected. Layer, material and groups of nodes are preserved in points.
One element-one line
Creates a geometrical line for each line mesh element and points.
Quadratic elements are converted like there were linears, ignoring mid-edge nodes
NURBS patches
This option converts all our mesh model (only surface mesh, triangles and quadrilateral) to a geometry model, obtaining a NURBS surfaces based definition. Creates a group of new layers called "Reconstruction", inside you will see two new layers: the first "All Lines And Points" contains lines and point and the second "Reconstructed Nurbs" the surfaces. If some surface couldn't be reconstructed it will appear a third layer called "SurfMeshes Not Reconstructed" containing the remaining parts converted in Surfmeshes, see more infomation about Surf Mesh.
One element-one surface
Creates a geometrical surface for each surface element (triangles or quadrilaterals) and its boundary curves and points.
Quadratic elements are converted like there were linears, ignoring mid-edge nodes
Nodes->grid surfaces
To create a grid of surfaces from a cloud of 3D nodes. The user will be asked for the cell size
The z of the grid will be extrapolated averaging a collection neighbor nodes
Triangles->grid surfaces
To create a grid of surfaces from a cloud of 3D triangles. The user will be asked for the cell size
The z of the grid will be get from the triangle where the grid corner is projected (in 2D), or from a close node.
Geometry Menu>Create>Object
Menu: Geometry->Create->Object
Toolbar:
With this command it is possible to create the following kinds of objects:

• Rectangle
• Polygon
• Circle
• Sphere
• Cylinder
• Cone
• Prism
• Torus

When creating an object, GiD asks for a center and a normal. To enter the coordinates of the center you can click on the screen or select an existing point (see Point definition ). To enter the normal, GiD displays a window where you can choose one of the three axes or enter the coordinates of a point.

Window to define the direction of the normal to the plane

The In screen button in the Enter normal window lets you manually enter the coordinates of the point which defines the normal: you can directly click on the screen or pick an existing point using the Join option in the Contextual mouse menu.
When using the commands sphere, cylinder, cone, prism or torus, the volume of the object is also created.
Geometry Menu>Create>Old types
Note: These old entities cannot be created from the menus or toolbars. It is still possible, however, to access to this function from the Right buttons.
Geometry Menu>Create>Old types>4-sided surface creation
The 4-sided surface has been substituted by the NURBS surface (see NURBS surface ). This new entity has all the functionality of the old one.
A 4-sided surface is an entity formed by a closed set of four lines in the space. Its mathematical definition is a bilinear Coon's surface. The surface is totally defined by the shape of the lines, with no information about the interior. This means that it will sometimes be necessary to use more surfaces to obtain a good shape definition.
To create a 4-sided surface, several lines must be selected (see Entity selection ). For the creation of a 4-sided surface defined by three lines, it is necessary to divide one of the lines into two pieces (see Divide ). The order of selection is not important, but all of them must join each other by sharing common points and they must form a closed contour. If it cannot be created, information about the endpoints is displayed in a window.
In order to make one or more lines form parts of a polyline (see Polyline ), select the entire polyline as one of the lines and GiD will automatically select the piece or pieces of the polyline that are required. Using this facility, non-conforming surfaces can be created. This means creating a surface by using the entire line on one side of the polyline, and creating more than one 4-sided surface by using parts of it on the other side.
When selecting more than four lines, GiD will automatically search for all the possible 4-sided surfaces that can be created with these lines. This allows the creation of many surfaces at the same time.
The Automatic button is equivalent to automatic 4-sided surface creation (see Automatic 4-sided surface creation ).
If the surfaces lie on the z=0 plane, the orientation of the surfaces will be anti-clockwise in this plane (normal vector points towards z positive). Otherwise, the orientation will be arbitrary. This can be checked with the DrawNormals command (see Normals (only Preprocessing) ).
The Number option lets you choose the label that will be assigned to the next created surface. If a surface with this number already exists, the old line changes its number.
Caution: When creating more than one surface at a time, some undesired surfaces may also be created. It is necessary to check the surfaces after creation and erase the undesired ones.
Geometry Menu>Create>Old types>Automatic 4-sided surface creation
The 4-sided surface has been substituted by the NURBS surface (see NURBS surface). This new entity has all the functionality of the old one.
Inside this option, GiD creates as many 4-sided surfaces as it can find. Every new surface will be created in the current layer.
Caution: When creating more than one surface at a time, some undesired surfaces may also be created. It is necessary to check the surfaces after creation and erase the undesired ones.

Geometry Menu>Create>Old types>Planar surface creation
The planar surface has been substituted by the NURBS surface (see NURBS surface). The latter automatically detects if boundary lines lie in a plane and creates a planar NURBS.
A planar surface is an entity formed by a closed set of lines, all of them lying on the same plane. These lines must share some common endpoints.
To create a planar surface, some lines must be selected (see Entity selection). The order of selection is not important but all of them must join each other by sharing common points and must form a closed contour. If all lines are not in the same plane the surface is not created.
It is possible to add holes to a planar surface. To do so, it is first necessary to create the outside planar surface. After this, press the Hole button and select the created surface. Then select lines that form every hole, one by one. Finish with escape. It is also possible to define the surface and holes at the same time, by selecting all the curves.
If the surfaces lie on the plane z=0, the orientation of the surfaces will be anti-clockwise in this plane (the normal vector points towards z positive). Otherwise, orientation will be arbitrary. This can be checked with the DrawNormals command (see Normals (only Preprocessing)).