Drafting Techniques

Drafting Techniques

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Distinguished Contributor
PatrickRoberts
Posts: 107
Registered: ‎11-10-2003
Message 1 of 5 (510 Views)

Scale Factor for Isometric viewport

510 Views, 4 Replies
09-15-2003 02:10 AM
I am trying to set up a viewport in paper space that has a scale factor set up for an isometric drawing. Here's the scenario: I have created a simple 3dsolid, 6'x6' at the base and 4' high in model space. I have created two viewports in paper space. One is the top view and the other is an isometric. Both viewports are set to 1/4" = 1'-0". When plotted, the top view scales 1 1/2" x 1 1/2" (which is correct). Yet the isometric view scales at 1 1/4" x 1 1/4" along the 30 degree lines. Isometrics, by definition, should be scaled correcly. What can I do to have the isometric view scaled correctly so I may scale items along their 30 degree lines. Any help would be appreciated. Patrick
*Elrod, Kent
Message 2 of 5 (510 Views)

Re: Scale Factor for Isometric viewport

09-15-2003 04:12 AM in reply to: PatrickRoberts
the scale factor for a viewport showing a 3d object
in an isometric view so that the object will scale "properly" or as
expected after plotting is
size=4>1.22474487


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
I
am trying to set up a viewport in paper space that has a scale factor set up
for an isometric drawing. Here's the scenario: I have created a simple
3dsolid, 6'x6' at the base and 4' high in model space. I have created two
viewports in paper space. One is the top view and the other is an isometric.
Both viewports are set to 1/4" = 1'-0". When plotted, the top view scales 1
1/2" x 1 1/2" (which is correct). Yet the isometric view scales at 1 1/4" x 1
1/4" along the 30 degree lines. Isometrics, by definition, should be scaled
correcly. What can I do to have the isometric view scaled correctly so I may
scale items along their 30 degree lines. Any help would be appreciated.
Patrick
Distinguished Contributor
PatrickRoberts
Posts: 107
Registered: ‎11-10-2003
Message 3 of 5 (510 Views)

Re:

09-15-2003 05:36 AM in reply to: PatrickRoberts
Kent
Thank you for the reply. It worked great. But why do you need to use that factor, and where did you find it?
Patrick
*Elrod, Kent
Message 4 of 5 (510 Views)

Re:

09-15-2003 07:44 AM in reply to: PatrickRoberts
There is a long discussion about this very thing in
the drafting newsgroup, you might want to read that entire thread.

 

In a nut shell, there are two types of isometric
drawings; ISOMETRIC PROJECTION and ISOMETRIC DRAWING.  In the bad old board
days and more recently drawing 2D isometrics with CAD more often than not an
ISOMETRIC DRAWING was created.  This involved taking the exact length of
the objects sides and drawing them that length along the isometric
axis.

 

ISOMETRIC PROJECTION involves the mathematical and
graphical method of actually rotating the object in an isometric type view and
then projecting the corners perpendicular to a plane of projection as seen from
infinite distance.  Imagine taking your 6x6x4 box and putting it behind a
piece of glass, now while you look perpendicularly through the glass, move the
box to that you can see the top, and right and left sides, I.E. and isometric
view.  Now, you can see that the lines that are formed where the planes
meet are foreshortened.  The edges are rotated away from your point of
view.

 

Autocad is doing exactly this when you create a 3D
object and then rotate it to view it as an isometric.  So when you view it
through a viewport, a scale of 1xp will give you a true ISOMETRIC
PROJECTION.   Due to this shortening involved when the object is
rotated, the lengths are shortened by an amount equal to sqrt of 2/3, so you
take the inverse of that in order to have the viewport scaling (XP) show the
object as a true size.

 

Kent


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
Kent

Thank you for the reply. It worked great. But why do you need to use that
factor, and where did you find it?
Patrick
*Graham, Rick
Message 5 of 5 (510 Views)

Re:

09-16-2003 11:06 PM in reply to: PatrickRoberts
Good explanation. Wonder if Inventor takes this
into account (but thats a different subject and newsgroup).

 

Rick


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">

There is a long discussion about this very thing
in the drafting newsgroup, you might want to read that entire
thread.

 

In a nut shell, there are two types of isometric
drawings; ISOMETRIC PROJECTION and ISOMETRIC DRAWING.  In the bad old
board days and more recently drawing 2D isometrics with CAD more often than
not an ISOMETRIC DRAWING was created.  This involved taking the exact
length of the objects sides and drawing them that length along the isometric
axis.

 

ISOMETRIC PROJECTION involves the mathematical
and graphical method of actually rotating the object in an isometric type view
and then projecting the corners perpendicular to a plane of projection as seen
from infinite distance.  Imagine taking your 6x6x4 box and putting it
behind a piece of glass, now while you look perpendicularly through the glass,
move the box to that you can see the top, and right and left sides, I.E. and
isometric view.  Now, you can see that the lines that are formed where
the planes meet are foreshortened.  The edges are rotated away from your
point of view.

 

Autocad is doing exactly this when you create a
3D object and then rotate it to view it as an isometric.  So when you
view it through a viewport, a scale of 1xp will give you a true ISOMETRIC
PROJECTION.   Due to this shortening involved when the object is
rotated, the lengths are shortened by an amount equal to sqrt of 2/3, so you
take the inverse of that in order to have the viewport scaling (XP) show the
object as a true size.

 

Kent


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
Kent

Thank you for the reply. It worked great. But why do you need to use
that factor, and where did you find it?

Patrick
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