A Look at Plan
by Glenn Ryan
Do not think it is used in 3d only. In
fact, 99.9% of drawings are still 2d, mine included, and I use the plan
command in 2d dwgs, not 3d. It's particularly useful for road layouts.
Imagine you had a road centreline that was going from bottom left of
screen to top right. Now when producing road alignment drawings,
paperspace generally has a viewport showing the road in plan (just a
term, not related to PLAN command at the moment), and another viewport
looking at the long section along the road centreline in modelspace.
This long section is usually spat out of a design program like Mx.
We'll concern ourselves with just the view of the road not the long
section. Now, to use space efficiently in the drawing layout, you would
want to show the road going as close to horizontal across your layout
(close meaning if it's curved then take best fit), so you could fit the
most amount of road metreage in the view. You can accomplish this by
using the UCS and PLAN commands. What follows is what I teach in my
All the steps following are in metric by the way, but the principle is
still the same. First of all setup a layout with title block and what
not. Then cut your main viewport that's going to show the top view of
the road like so:
Notice that the coordinate system in
the viewport is still WCS as denoted by the icon.
Next thing is to decide what scale you would like to show the road at -
a typical scale being 1:500. Now this is where people start to get lost
in viewport scales, because what I'm doing here is not only done in
mteric but also in METRES. That means paperspace plot scale is in
millimetres, but model is drawn at 1 unit = 1 metre. This is common
practice in the metric system with civil. In effect my road model is
1000 times smaller that the equivalent millimetres drawing (if a
structures person had done it for instance).
If the people in the class are really with it and are advanced, not just
attending the class, then I explain the next method, otherwise I just
explain UCS and PLAN command for view twisting.
I then put a rectangualr poly over the top of the viewport, then make a
block of it with an insertion usually mid left or sometimes mid left but
offset towards right. This block is then measured along the centreline
poly of the road at the correct scale. So, if the drawing was in
millimetres the viewport scale is a straight 1/500xp which is 0.002, but
seeing as we're in METRES the scale works out to this 1/ (500/1000) =
1/0.5 = 2xp.
Now that we have that knowledge, we can make our block at 0.5 scale
(1:500m), then flip to model and use the measure command with sub
command of block, to place the block along the poly like so:
Some of the blocks will need to be
manually rotated but that's no big deal. Now, while still in model tab,
rotate the UCS about the z axis to match the alignment of the first
Now that we have the UCS rotated to
where we want it, just issue the PLAN command and hit enter for the
default of current, so we end up with the drawing looking like so:
Now what I do is save a view of the
desired block. I do this in the view command by defining a window and
pick bottom left and top right of the block. Now we flip back to
paperspace, jump into our viewport and issue the VIEW command and
restore our view to the viewport and voila, the viewport is scaled
correctly and rotated like so:
This is the inherent beauty of using
views - they preserve they're UCS (if ticked in view dialog), but more
importantly their viewtwist angle. Then you just repeat the process for
as many blocks and layouts you want in this dwg. Of course I would have
road model as xref and have separate dwg file for each plan layout I
wanted, but the principle is the same. When you get the hang of it, it's
a very fast way to layout a series of dwg's.
A cautionary note: If you ever want to id points in the model (as it
would have been surveyed on coord system) make sure to reset your UCS to
WORLD before doing so, otherwise coords will be wrong.
if you want to reset your view to WCS plan, just enter UCS then hit
enter for default of world. Next use PLAN command and hit enter for
default of current ucs (WCS in this case) and you're back to plan view
The only other command I use in this process is the view sub option of
UCS. It will realign your UCS so that XY plane is perp. to viewing
- Establishes a new coordinate system
with the XY plane perpendicular to your viewing direction (parallel
to your screen). The UCS origin remains unchanged.
You would typically do this if you had
changed to WCS in viewport for some reason, but then wanted to put some
text in horizontally - like a note. UCS then V and you're away again.
I hope this has explained the UCS and PLAN commands a bit for you. PLAN
generally sets the VIEWTWIST angle.