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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
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- 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.
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- 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.
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- 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:
- 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.
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