Most of the operations involved in moving around the drawing area are
embodied in one command called ZOOM. This command has a number of options
as set out in its data prompt:
All/Centre/Dynamic/Extents/Left/Previous/Vmax/Window/<Scale(X/XP)>:
Each of these options is described in the following paragraphs.
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Zoom Scale
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This is the default option and simply requires the entry of a number which
represents a magnification factor. Note that the factor is applied to the
entire drawing (as defined by the LIMITS command). Numbers less than 1
will reduce the displayed size of the drawing, while numbers greater than
1 will enlarge it. If "x" is inserted after the number (viz. 0.8x) then
the factor is applied to the current view. If "xp" is inserted after the
scale factor, then the view is scaled relative to paper space (this is
useful for zooming a view within a paper space viewport to a specific scale,
for example, "0.1xp" will produce a view of model space at a scale of 1:10
relative to paper space).
Zoom Extents
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This option causes AutoCAD to display all the graphics that is contained
in the drawing (referred to as the drawing extent) with the largest image
possible. It does not necessarily extend to the defined drawing limits.
Zoom All
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This option causes AutoCAD to display the whole drawing as far as its drawing
limits or drawing extents (whichever is greater).
Zoom Window
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This option prompts the user to point to the lower left and upper right
corners of a box on the existing view in order to define that part which
is to be enlarged to fill the display.
Zoom Centre
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This option requires a point which is taken to be the centre of the new
display, followed by a value to be its new height in drawing units. The
existing height is offered as the default for the new height to allow for
panning across the drawing. If the new height is followed by "x" (viz.
2x), then it is taken as a magnification factor relative to the current
height. If followed by "xp", then it is taken as a scale factor relative
to paper space and can be used for scaling the contents of paper space
viewports.
Zoom Left corner
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This option operates in the same way as "ZOOM Centre" except that the point
specified is taken as the lower left corner of the new display.
Zoom Previous
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This option reverts to the displayed view prior to the current one. For
the purpose of this option, up to 5 views are "stacked" so that the last
five views can be recalled.
Zoom Dynamic
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This is the most powerful ZOOM option once it is understood. It permits
very quick movement around the drawing.
Once selected, this option clears the graphics area of the screen and
displays three rectangles. The solid white (or black) box denotes the extent
of the current drawing. The magenta box shows the current view. The four
corners shown in red indicate the region within which rapid views can be
produced (there is a speed advantage in staying within these four corners).
Also on the screen will be a dynamic view box (with an "X" in the middle)
which moves as the mouse is operated (this is referred to as pan mode).
This view box should be positioned so that its lower left corner is at
the lower left corner of the view required. By pressing the "pick" button
on the mouse, the "X" is replaced by an arrow pointing to the right side
of the view box. This indicates zoom mode. As the mouse is moved, the view
box shrinks and expands so that the size of the required view can be set.
The "pick button" toggles between PAN and ZOOM mode so that fine adjustments
can be achieved. When the view required has been selected, press RETURN
to cause AutoCAD to display it.
Another very useful command that can be used to alter the currently displayed
view is the PAN command.
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Pan
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This command permits panning across the drawing without changing the display
scale. A displacement must be specified either by pointing or typing.
Three other commands are available for creating 3D views of the drawing.
These are really only of interest if you have taken the trouble to enter
a three-dimensional description of an object. However, even if your drawing
is only 2D, you can still look at it from any 3D point in space and view
it as either a parallel projection or as a full perspective.
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Vpoint
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This command is used to establish a view from a viewpoint located anywhere
in space. The viewpoint can be entered as a 3D point, a spherical point
(horizontal and vertical angles relative to the target - normally the origin)
or specified dynamically (by pressing RETURN instead of entering a point).
The resultant view is always shown as a parallel projection and assumes
that you are "looking at" the origin (which is then referred to as the
target). The target can be changed, but the process involved is beyond
the scope of these notes.
Dview
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This command provides a dynamic tool for setting up a view of a 3D object
as either a parallel projection or a perspective. It uses a camera and
target concept to manipulate the viewing position, direction of view, focal
length (effecting field of view) and viewing distance. This tool also supports
front and back plane clipping and hidden line removal.
Plan
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This command provides a convenient way of getting back to a normal plan
view after working in 3D.
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| One of the fundamental concepts in AutoCAD is the distinction that
is drawn between model space and paper space. The notion is that when you
are drawing, whether in 2D or 3D, you are generally building a model of
the entity that you wish to represent. A plan, elevation or section is
simply a type of model which is drawn in model space in the same way as
you might draw a 3D representation of the object you wish to represent.
Whether the model is 2D or 3D, it is constructed in real units representing
its actual size. Once the model is complete (or at least partially complete),
AutoCAD allows you to switch to paper space where all drawing is done at
full size in paper units. In paper space, you are able to construct one
or more rectangular viewports, each containing an independent scaled view
of the model (or part of the model). You can, of course, switch back and
forth between paper and model space, and you can also draw directly in
paper space to set up borders and title blocks, etc.
One of the confusing things in AutoCAD is that the term "viewport" has
a different meaning depending on whether you are working in model space
or paper space (though the two ideas are related, as you will see!!).
When working in model space, viewports are used to sub-divide the drawing
area on the screen so that the user can work with several views of their
drawing (or model) at the same time (and move at will between them).
When working in paper space, viewports are used to represent rectangular
areas of the paper (or sheet) in which views are displayed of the drawing
contained in model space. These viewports are treated as editable entities
which can be scaled, moved, stretched, copied or erased. These viewports
can also overlap or have space between them.
To control this mechanism, AutoCAD maintains a system variable called
TILEMODE. When this variable is equal to 1 ("on"), then one or more viewports
are displayed on the screen in a "tiled" pattern and therefore serve to
subdivide the drawing area to display different views of model space (equivalent
to the first function described above). When this variable is set equal
to 0 ("off"), then viewports are used to define regions in paper space
where views of the model are displayed.
When TILEMODE is on, the user is necessarily working in model space
(albeit with one or several viewports). When TILEMODE is off, the user
can work in paper space or model space: use paper space to create, position
and size viewports or to add/edit paper space graphics; or switch to model
space and choose a (paper space) viewport and edit the model within it.
The commands available to manipulate these concepts are listed below.
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Tilemode
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This command is used to set the value of the system variable of the same
name. Its primary purpose is to control the way in which AutoCAD handles
viewports. If TILEMODE is switched off (set to 0), then AutoCAD switches
to paper space. If no viewports have been created in paper space, then
AutoCAD will remind the user to create at least one viewport. Once that
has been done, the user can switch between paper space and model space
as described above. If TILEMODE is switched on (set to 1), then AutoCAD
switches to model space and displays the view (or set of tiled viewports)
that was most recently active. Paper space entities are not visible when
working in model space with TILEMODE "on".
Vports
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This command only functions when TILEMODE is "on". It allows you to establish
up to 16 viewports on the screen such that each viewport can hold a different
view of your drawing. Once set up, you can only work in one viewport at
a time, but it is easy to move between them: simply move the cursor to
the desired viewport and click the left mouse button.
View
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This command saves the current view of the drawing under a user-defined
name or restores a view that was previously saved in that way. It can be
used in both model space and paper space. For example, if you are currently
zoomed in on a particular part of a drawing and you think that you will
later want to get back to that view, then you would use this command. Viewport
configurations (created by VPORTS) can be named, saved and restored in
the same way as individual views.
Mview
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This command is used when TILEMODE is "off" to create and define the characteristics
of viewports in paper space. Once created, viewports can be turned "on"
or "off": when off, there is no attempt to display the view that they contain,
so that they can be manipulated without having to redraw their contents
all the time. Viewports can also be linked to existing "views" saved using
the VIEW command (see previous). Finally, viewports can be tagged so that
AutoCAD automatically does a hide in that viewport every time the drawing
is plotted.
Mspace
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This command is used when TILEMODE is "off" (and paper space is active)
to allow you to switch to model space and edit your drawing inside one
of the paper space viewports. There must be at least one viewport "on"
and active for this command to work. Control switches to one of the active
viewports, displaying the cross-hair cursor and permitting you to edit
your drawing within that viewport. You can switch between viewports simply
by clicking on them (in the same way as for tiled viewports when TILEMODE
is "on").
Pspace
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This command is used when TILEMODE is "off", but model space is active
(due to the use of the command MSPACE), to allow you to switch back to
paper space and add or edit graphics within that drawing environment.
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