From BlenderWiki

Perspective and Orthographic Projection

Description

Each 3D viewport supports two different types of projection. These are demonstrated in (Orthographic (left) and perspective (right) projections.):

Orthographic (left) and perspective (right) projections.

Our eye is used to perspective viewing because distant objects appear smaller. Orthographic projection often seems a bit odd at first, because objects stay the same size independent of their distance. It is like viewing the scene from an infinitely distant point. Nevertheless, orthographic viewing is very useful (it is the default in Blender and most other 3D applications), because it provides a more “technical” insight into the scene, making it easier to draw and judge proportions.

Options

To change the projection for a 3D view, choose the View » Orthographic or the View » Perspective menu entry. The 5 NumPad shortcut toggles between the two modes.

Demonstration of camera view.

The View » Camera menu entry sets the 3D view to camera mode (0 NumPad). The scene is then displayed as it will be rendered later (see Demonstration of camera view): the rendered image will contain everything within the outer dotted line. Zooming in and out is possible in this view, but to change the viewpoint, you have to move or rotate the camera.

Technical Details

Perspective definition

A perspective view is geometrically constructed this way: you have a scene in 3D and you are an observer placed at a point O. The 2D perspective scene is built by placing a plane, a sheet of paper where the 2D scene is to be drawn in front of point O, perpendicular to the viewing direction. For each point P in the 3D scene a PO line is drawn, passing by O and P. The intersection point S between this PO line and the plane is the perspective projection of that point. By projecting all points P of the scene you get a perspective view.

Orthographic definition

In an orthographic projection, you have a viewing direction but not a viewing point O. The line is then drawn through point P so that it is parallel to the viewing direction. The intersection S between the line and the plane is the orthographic projection of the point P. And by projecting all points P of the scene you get the orthographic view.

View Shading

Description

Depending on the speed of your computer, the complexity of your scene, and the type of work you are currently doing, you can switch between several drawing modes:

A 3D view’s draw mode button.

Textured

Displays UV image textured models with OpenGL lighting. Neither procedural textures nor texture mapped differently will be shown.

Shaded

Approximates all textures and lighting at each vertex, and blends from one to the next. Much less accurate than using the render engine to check textures, but much faster. Note that if you have no lighting in your scene, everything will remain black.

Solid

Surfaces are drawn as solid colors, with built-in OpenGL lighting (not dependent on scene light sources, it is set in the User Preferences window, System & OpenGL tab, Solid OpenGL lights group of controls, see this page). This is the default drawing mode.

Wireframe

Objects only consist of lines that make their shapes recognizable (e.g. the edges of meshes or surfaces…).

Bounding Box

Objects aren’t drawn at all. Instead, this mode shows only the rectangular boxes that correspond to each object’s size and shape.

You can switch between these draw modes by:

• Using the Draw type drop-down list in the 3D views’ header (A 3D view’s draw mode button).
• Pressing D to pop-up the Draw mode menu.
• Using the Z-based shortcuts as detailed below:

View Clipping Border

Description

To assist in the process of working with complex models and scenes, you can change the view clipping to visually isolate what you’re working on.

This tool will only display what is inside a volume defined by you.

Once activated with AltB, you have to draw a rectangle with the mouse, in the wanted 3D view. The created clipping volume will then be:

• A right-angled parallelepiped (of infinite length) if your view is orthographic.
• A rectangular-based pyramid (of infinite high) if your view is in perspective.

To delete this clipping, hit another time AltB.

Example

Region/Volume clipping.

(Region/Volume clipping) is an example of using the clipping tool with a cube. Start by activating the tool with AltB, see “Start” in the upper left. This will generate a dashed cross-hair cursor. Click with the LMB and drag out a rectangular region shown in the upper right. Now a region is defined and clipping is applied against that region in 3D space. Notice that part of the cube is now invisible or clipped. Use the MMB to rotate the view and you will see that only what is inside the pyramidal volume is visible. All the editing tools still function as normal but only within the pyramidal clipping volume.

The gray area is the clipping volume itself. Once clipping deactivated with another AltB, all of 3D space will become visible again.

Background Image

Description

To have a background picture in your 3D view is very helpful in many situations: modeling, obviously, but also painting (e.g. you can have reference pictures of faces when painting textures directly on your model…), animation (when using a video as background), etc.

• They are specific to their window (i.e. you can have different backgrounds for each of your 3D views, e.g. top/front/side images for relevant views…).
• They are only available for Top, Side and Front (and their complementary versions) orthographic views! The picture remains the same when you switch between these six views.
• Their size is related to the window’s zooming factor (i.e. they grow big when you zoom in, etc.).
• You can use video files and animated sequences.

The default, empty Background Image panel.

The Background Image panel in use.

Blender manages this feature through the Background Image floating panel, shown with the View » Background Image... menu entry. By default (The default, empty Background Image panel), this panel only has one Use Background Image button, that toggles on/off the whole feature.

Once enabled (The Background Image panel in use), you have the background-specific settings on top, and below, a standard image datablock set of controls:

• Use – Disable this to turn off background image.
• Blend – This slider controls the transparency of the background image (from 0.0' – fully opaque – to 1.0 – fully transparent).
• Size – Controls the size, or scale, of the picture in the 3D view (in Blender units).
• X Offset, Y Offset – The horizontal and vertical offset of the background image in the view (by default, it is centered on the origin), in Blender units.

The other controls are common to most image datablock ones, and are fully documented in the texture chapter. Let’s just say that you can load (Load button) an image or use an already existing one (double-arrow button), use static, movie, sequence or generated images, and so on…

Use Lo-Res Proxy

To improve PC performance when using background images you may have to use lower-resolution proxies. If your monitor resolution is 800×600, then the background image, full screen, without zooming, only needs to be 800×600. If your reference image is 2048×2048, then your computer is grinding away throwing away pixels. Try instead to take that 2k×2k image, and scale it down (using Blender, or Gimp) to, for example, 512×512. You will have sixteen times the performance, with no appreciable loss of quality or exactness. Then, as you refine your model, you can increase the resolution.

Example

Here is an illustration of the background image feature:

An example of background image.

As this is a video file and Auto Refresh is enabled, when you change frame or hit AltA, the background picture follows or is played back…