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# VIEW

Visualization commands change the way to display the information in the graphical window. They do not change any definition of the geometry or any other data.

Generally, they can be used within any other command without leaving it. When the visualization process finishes, the first command continues.

They can be accessed either from the top menu `View` or form the right mouse button.

## Zoom

Zoom is used to change the visualized size of the objects without deforming them. This only enlarges or reduces the objects and changes the orthogonal perspective of the window.

- `Zoom in:` Pick inside the graphical window. A dynamic rectangle is opened. Pick again and the visualization changes to display only the part within the defined rectangle.
- `Zoom out:` Pick inside the graphical window. A dynamic rectangle is opened. Pick again and the visualization changes so that everything in the graphical window is reduced to the size of the rectangle.
- `Zoom frame:` Choose a visualization size so as to display everything inside the window.
- `Zoom points:` User enters two points (see section Point definition), and a visualization size is chosen so as to display these two points inside the window.
- `Zoom dynamic:` Moving mouse horizontally, view is enlarged or shortened.
- `Zoom previous:` GiD goes to the previous saved zoom.
- `Zoom next:` If one previous zoom has been made, this option goes to the one after the current view in the stack list.

`Note:` Instead of picking twice to begin and end the rectangle, it is possible to maintain the leftmouse pressed and move the cursor.

## Rotate

There are various ways to make a rotation in order to change the graphical view of the geometry, without changing it.

`Note:` Instead of picking twice to begin and end the rotation, it is possible to maintain the leftmouse pressed and move the cursor.

### Rotate screen axes

With this option, a dynamic rotation about the screen axes is made. Screen axes are defined as:

- `X-axis`: A horizontal axis.
- `Y-axis`: A vertical axis.
- `Z-axis`: An axis orthogonal to the screen.

When entering this command, `Z-axis` is set by default and moving the mouse to the left or to the right will rotate the geometry around this axis. Picking the left mouse changes the axis. To leave this function, use `escape` (see section Escape).

To change the axes is also possible by entering the letters `x`, `y` or `z` in the command line.

To move the geometry by a fixed angle, enter the number of degrees, positive or negative, in the command line.

### Rotate object axes

With this option, a dynamic rotation about the object axes is made. Object axes are the global axes in the position they are in that particular moment. i.e. the axes currently drawn in the graphical window.

When entering this command, `Z-axis` is set by default and moving the mouse to the left or to the right will rotate the geometry around this axis. Picking the left mouse changes the axes. To leave this function, use `escape` (see section Escape).

To change the axes is also possible by entering the letters `x`, `y` or `z` in the command line.

To move the geometry by a fixed angle, enter the number of degrees, positive or negative, in the command line.

### Rotate trackball

With this option, a dynamic rotation is made, resembling a trackball device. It means that when picking over a geometry point with the left mouse and moving the mouse, the geometric point tries to follow the mouse pointer. This can be imagined as a ball over the graphical window which is moved with the mouse.

The left mouse button can be pressed several times to connect and disconnect the movement. To leave this function, use `escape` (see section Escape).

### Rotate angle

The new position of the geometry after the rotation can be defined as the direction orthogonal to the screen via a pair of angles:

1. The angle in the plane `XY` starting from the `X-axis`.
2. The elevation angle from the `XY` plane.

As an example, the initial view (orthogonal to the Z-axis and with the X-axis horizontal) can be obtained with:

    rotate angle 270 90

### Rotate points

This option appears only in the right side commands menu.

The new position of the geometry after the rotation can be defined as the direction orthogonal to the screen via a pair of points:

1. The target point, the point to look at.
2. The view point, the point to look from.

### Rotate center

The default center of rotation is defined approximately in the center of the geometry.

If it is desired to change this center, use this command and enter a point (see section Point definition). This new rotation center will be maintained until the next `zoom frame` (see section Zoom).

### Rotate original view

This option, that appears only in the graphical pop-up menu, changes the view to the original one: screen orthogonal to the Z-axis with the X-axis lying horizontally and pointing to the right.

## Pan

- `Two points:` With this command, the location of the geometry is displaced in the graphical window. To do this, pick two points in the graphical window.
- `dynamic:` In this case the displacement is made dynamically, moving the mouse horizontally.

## Redraw

This command redraws the geometrical model in the graphical window. For those machines that include overlays, all the layers that stay underneath are not affected, so the redraw goes faster and the underneath drawings remain untouched.

## Render

By using this option, the way of viewing the model changes. There are four options:

- `Normal:` This is the usual way of visualizing. The geometry and mesh are viewed including all definition lines.
- `Filled:` Solid model with no illumination and lines.
- `Flat lighting:` Solid model with flat illumination and lines.
- `Smooth lighting:` Solid model with smooth illumination (better quality).

Note: The rendering of a volume mesh requires the option `View boundaries` (see section View boundaries).

Note: Quality of visualization is controlled via preferences (see section Preferences).

Note: The light vector direction can be changed interactively with the menu option `Change Light Vector` inside the menu `Utilities` (see section Change Light Vector).

## Label

With this option, the labels of the entities are drawn or not. It is possible to select some entities or to apply this option to all entities viewed in the graphical window. To select some entities, choose `select` before applying on the `Points`, `Lines`, `Surfaces` or `Volumes`. Then, select entities in the usual way (see section Entities selection). Options are:

- `All:` All entities in the graphical window will have their labels drawn.
- `points,lines,surfaces` or `volumes:` If `select` is not set, all the entities in the graphical window will have their labels drawn.
- `Off:` Finish drawing labels for all entities.

## Entities

With this option, it is possible to choose some of the `points, lines, surfaces or volumes` to be drawn. It is useful to make drawing faster or clearer in some instances.
Note: this option is only available in the right buttons menu. (see section USER INTERFACE)

## Layers

Layers are a way to split a complex drawing into separate pieces. The idea is that any entity can belong to one layer or to none (an entity cannot belong to more than one layer). Then, it is possible to view only some layers and not others. It is also useful to easily select entities in the graphical window.

Layers window operations

Commands related to layers are:

- `New:` Creates a new layer. If name is given the layer is called "`Layer#`". The new layer will be used as the default layer until the end of the session or until it is changed.
- `Layer To use:` Selects a layer to be used as default. All the new entities will be created within this layer. All the layers are capable of being selected.
  Next to the `Layer To use` button, there's an arrow facing down. This is a menu which lets you select a point, a line, a surface or a volume; the layer to which it belongs that entity, will be set as the default layer.
- `On:` Entities belonging to this layer will be drawn and can be selected in the graphical window.
- `Off:` Entities belonging to this layer will not be drawn and cannot be selected in the graphical window.
- `Lock/Unlock (Freeze/Unfreeze):` Entities belonging to this layer will be drawn but cannot be selected in any way. When copying entities (see section Copy) and sharing old entities, entities belonging to frozen layers are not taken into account and not even a range of numbers (see section Entities selection) can be selected. The opposite command is `Unlock`, where the entities belonging to this layer can be selected, copied and shared.
- `Delete:` Deletes a layer. A layer can only be deleted if it has no entities in it.
- `View:` Gives information about the layer.
- `Entities:` Moves entities to a new layer. No new entities are created. They are only moved from one layer to another. When choosing, in geometry mode, `point`, `line`, `surface`, `volume` or `all`, option `all` can be used only to select entities in the graphical window and change all the entities in the dynamic box to the new layer. In mesh mode, it is possible to choose `nodes`, `elements` or `all`.
  Especial option `Also lower entities` permits to send to the layer also the entities that are lower entities of the selected ones.
  Example: If this flag is set and one surface is selected, its lines and its points are also sent to the layer.
- `To back:` Sends entities to the back of its layer. When an entity is "at the back" it's not visible and cannot be selected, moved, copied or deleted. To bring again the entities of a layer "to the front", select a layer and choose the `Bring to front` option, from the `To back` menu. There is another option, `Bring ALL to front`, which brings to front all entities of all layers.
  If the flag `Opposite` is set, entities which are not selected will go to the back.
- `Color:` Change color to layer. This color is used when making a render (see section Render).
- `Sel...:` In the layer window, there is the option `select` that allows the selection of several layers. This can be useful when using a large number of layers. After pressing `Sel...` a new window appears to allow the input of a pattern that will match the layer's name. In this pattern, characters * and ? are wildcards that match any characters or character, respectively, in the layer's name. So, the pattern `select` will match `select`, `selection`, `select-surface` and so on.
- `Rename:` Changes the name of a layer.
- `Close:` Closes the Layers window.

Important: The mesh generation does not depend on the state of the layers when the generation is performed (see section Layers). All layers are meshed and every node and element will be assigned to the layer where the original geometrical entity was. The only exception to this rule is for the case of frozen layer if the option `No mesh frozen layers` is selected.

## Save/Read View

These two options permits to save the actual view configuration into a file. Then, that configuration can be loaded using the `Read View` command.

## Background Image

An image can be used as background of GiD for visualization purposes (supported image formats are `.bmp` and `.ppm`). There are the following options:

- Fit screen: an image will be fitted into GiD's background window.
- Real size: the image will not be deformed; the image is placed in a plane. Three points must be entered: two of them to define the line where the bottom line of the image lies, and a stand-up point, which defines the upper direction of the image.
- Default: use this option to use the default background.

## Multiple windows

Command `Multiple windows` permits to have several views of the same project. Different views can be displayed inside the program main window or in supplementary windows.

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