CADD Tips & Tricks: Lost in Space: AutoCAD's Paper Space/Model Space Conundrum Explained
Professional Surveyor Magazine - Jan/Feb 1999
R. J. Zimmer, LS
Multiple perspectives and various scale plots on a single sheet are simple to create and modify with AutoCAD's paper space. The basic premise for paper space is to create a virtual
sheet of paper on which to develop a layout of your model
. The model is the basic AutoCAD drawing of your subdivision plat, a digital terrain model, a record of survey or your version of the ultimate survey vehicle. On the virtual paper you create views of your model at any (and even differing) scale and place extraneous information such as title blocks, scale blocks, north arrows and so forth. You can compose the entire layout, including placement, size and scale of views, to see how it all looks before sending it to the plotter or printer.
The advantages to this are twofold. One advantage is that setting up a sheet for plotting multiple views of the model is simplified. You can create them all on a single sheet by creating viewports in paper space. These viewports are like having video monitors that show what the model looks like from different angles and zoomed in or out. Only one model is needed, but it can be viewed and plotted with as many viewports from as many angles or scales as desired (up to 48 or the limits of your AutoCAD variable setting of MAXACVTP). It's also easier to select a scale that will fit on the size sheet to which the drawing will be plotted and vice versa, selecting the right sheet size for the desired plot scale.
The other advantage is that the extraneous objects in paper space do not become part of the model. You can keep all the cartographic clutter away from the real data. For instance, you can add items such as north arrows and scale blocks to a topographic drawing of an area, yet keep them separate from the topographic data model by using paper space as the virtual paper for plotting purposes. If this topographic model is later merged with another AutoCAD drawing (Figure 1), the paper space objects are "left behind." That is, they will not show up at all in the new drawing. This is appropriate because the title block, scale, north arrow and so forth are useful only on a plot of the model, so it makes sense to not embed these objects in the data model itself. I have seen planimetric topographic maps that were a series of panels as separate AutoCAD drawings, each of which had sheet borders, title blocks, scale, logos and other items embedded in model "space." When these panels were tiled into a single drawing, all these overlapping borders, title blocks, scales and logos also appeared in the drawing. This added a lot of unnecessary overhead for AutoCAD and it looked ugly! Many layers had to be turned off or frozen before the relevant data was clearly visible.
Creating the Paper Space Viewport(s)
AutoCAD has two settings for the tilemode system: variable 1, or on, and 0, or off. The default setting is 1, which forces AutoCAD to be in model space exclusively. With tilemode set to 1, viewports may be created with the VPORTS command. These viewports will be tiled and automatically sized by AutoCAD to fill the entire graphics window. Think of bathroom tiles that abut each other—they do not overlap. These model space viewports will not be editable in any way; that is, you will not be able to move, resize or place them on separate layers or assign them colors or linetypes. They are a simple tool used primarily for viewing a 3D model while constructing it (for example, a part assembly).
Setting Tilemode to 0 (off) allows you to create non-tiled viewport objects that can be edited and may overlap. Set tilemode to 0 by doing either of the following:
New value for TILEMODE <1>: 0
Variable name or ? <TILEMODE>: tilemode
New value for TILEMODE <0>: 0
To create the viewport (now that tilemode is set to zero), use the MVIEW command.
The default option is to create a viewport by picking a point (first point), then picking the opposite corner. Doing this will create a viewport on the current layer, with the current linetype and color, and the viewport will be the size you made it and in the location you put it. Any of those characteristics can be changed at any time by using standard AutoCAD editing commands, such as move, scale, chprop and so forth The previous model space view of the model will now be displayed inside the viewport.
In and Out of Model Space
When tilemode is to 1 (on), you can only be in model space. When tilemode is set to zero (off), you can "move" between model space and paper space. To get to model space, type the command MSPACE. When tilemode is set to zero and you are in model space, the UCS icons will show up in the viewport(s) rather than in the corner of the graphics editing area. That's a helpful clue to where you are. You may also see the word MODEL in the status bar at the lower portion of the screen. To move back to paper space, type the command PSPACE. It's that simple. If you try to enter the command MSPACE or PSPACE when tilemode is set to 1 (on), you will see an error message that says: **Command not allowed unless TILEMODE is set to 0.**
In paper space, the crosshairs can move over entire graphics. In Model Space, the crosshairs travel only to the edges of the current viewport and become an arrow outside the current viewport (in the rest of paper space or in other viewports). If you have more than one paper space viewport, only one may be current at a time. To make a viewport current, simply move the cursor over the viewport and click the pick button on your mouse. The arrow will then change to the crosshairs in the viewport.
Zooming Around in Space
When tilemode is set to zero, it is possible to zoom and pan in either model space or paper space. The tricky part here is to not get lost. In paper space, you can zoom or pan around the virtual sheet and can zoom in very close to the title block, for instance. Note: You cannot do transparent zooms in paper space (a transparent zoom is one that occurs while in the middle of another command such as move or copy). Typing the command MSPACE brings you to model space in one of the viewports. You can then pan or zoom (transparently) within this viewport. The display you set in one viewport has no effect on the display in the other viewport(s).
Here's a good way to get lost in space: in paper space, zoom in very close on one of the viewports. Then enter model space with the MSPACE command. Now zoom and pan around in that viewport, save and close out the drawing and go home for the weekend. Come back Monday morning after you've had a chance to forget what you did the previous Friday, open your drawing and VOILA! You can't find the rest of the stuff in the drawing. Zoom to extents—still nothing! Panic! Something ate the drawing over the weekend!
Relax. It's not so bad. Go to paper space, then zoom extents. Now everything comes back. You just had your face too close to the TV screen and couldn't see the rest of the picture. I've seen this happen way too many times. Don't get lost in space! You should enter model space with tilemode set to zero only to set up the viewport display and scale. You should do the editing of your model with tilemode on (set to 1). That will not only help you avoid getting lost, but it will preserve the viewport settings for your plot.
Scaling the Model in the Viewport
Different scales are achieved in a viewport by adjusting the zoom factor of the viewport display as a ratio of the paper space scale. The AutoCAD command is: zoom scaleXP, where the XP means times paper space and tells AutoCAD to scale the display in the viewport relative to paper space rather than model space (you may need to pan around your model after zooming in or out to adjust the display of your model). For example, to set the scale to 1:100 in the viewport the command would be zoom 1/100XP. Note: keep in mind that your paper space and model space units may be different. Typically paper space units are inches or centimeters. If your model is in architectural units, you will need to multiply your scale factor by 12 to get the correct scale. For instance, zoom 1/24XP will create a plotted scale of 1/4" = 1 foot in that viewport. Paper space entities (and text sizes) should be scaled 1:1 and the plot should be scaled 1:1 to simplify scaling and plotting the model.
The visibility of various layers can be controlled individually for each viewport. That is, one viewport may show all the layers, and another may show only a few. Figure 2 shows multiple viewports. The lower left viewport shows only the house layers.
To control the visibility of layers, use the command VPLAYER, instruct AutoCAD to freeze (or thaw), tell AutoCAD which layer (or layers), then select the viewport or viewports to which to apply the layer settings.
Layer(s) to Freeze: land
Select objects: 1 found
Because the paper space viewports are editable AutoCAD objects, their layer can also be turned on or off. This is done using the regular AutoCAD layer command. This affects the visibility of the viewport's border only, not the contents of the viewport. The model displayed inside the viewport will still be visible.
If desired, you can shut off a viewport just like switching off a video monitor. This is the off option in the MVIEW command. Shutting a viewport off blanks it out. It does not affect the visibility of the viewport's outline (border).
To shut off a viewport do the following:
ON/OFF/Hideplot/Fit/2/3/4/Restore/<First Point>: off
Select objects: 1 found
Hidden Line Removal
You can instruct AutoCAD to remove hidden lines from viewport objects at plot time. To do this use the MVIEW command's HIDEPLOT option and select the viewport. You won't see anything different on the screen after you do this, but you will when you plot.
That wraps it up for paper space and model space.
Don't get lost in space—remember to watch those icons!
Rj Zimmer is a consultant based in Helena, Montana, providing AutoCAD support as well as customizing, programming and GIS services. He is also a Contributing Editor for the magazine.
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