Weekly Pearls
What follows will be my personal contribution to the body of
knowledge in the form of weekly tips to make your Rhino modeling
more productive and FUN! I will make every effort to
update this page every Sunday, which will make it easy to
remember, since that's when I also complete reviews of
submissions from my students in the Proboat eLearning course,
Modeling in Rhinoceros for Marine
Designers.
I've been compiling the list of items for some time and I am
now ready to begin composing the tips. Each tip will focus
on some facet of modeling, usually (though not always) marine
related. At the outset, the tips will probably target the
freshman level Rhino practitioner, since most of them came to me
as I was creating and updating the Proboat course.
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Weekly Pearls (click links to
take you to the topic of interest).
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7/5/2010
This week, we will investigate a feature that can make it
much easier to edit surfaces that have many control
points. To begin, download
this model and open it. In it you will find
a surface that is taken from one of the sample models
distributed with the plugins, RhinoStatics and
RhinOffsets.
Select the surface and turn on the control points
(PointsOn). Your Perspective viewport should resemble Fig
1.
Fig 1 Hull with control points and Isocurves
displayed.
In the figure, you will note there are 16 control points at
each "station". They are not really stations,
but since they are almost transverse, we will refer to them as
stations. In the author's estimation, this is entirely too
many points to make the hull easy to edit, but they are there
just to make the point about SoftEditSrf command.
In the figure, select the control point at the garboard
(the one highlighted in the figure) and move it up 1" by
nudging or dragging it to effect a more hollow shape to the
hull. It should resemble something like Fig 2.
Notice when you move the control point, its neighbors do not
move, causing an unsightly dimple where the control points used
to be.
Fig. 2 Edit control points
Undo the previous move and select the point on the same
"station" just above the keel. Now, in the Front
viewport (Fig 3), move this point up one inch and watch the edge
of the surface. It changes, which is very alarming, since
the designer went to great lengths to make this edge fair and
smooth. Your Front viewport should now resemble Fig 4.
Fig 3. Right Viewport Before editing Control
point 2
Fig 4 Front Viewport with control point 2
moved one inch up.
Notice in Fig 4 how the edge of the hull is now higher above
the first control point than it was in Fig. 3, indicating that
it will be difficult to use this control point to help getting
the hollow in the garboard.
Undo the previous move and press escape until the control
points are no longer visible. Now issue the SoftEditSrf
command. At the prompt, there are some options to
investigate. The first option is the U_Distance
option. In the case of this surface, the U Direction is
almost transverse. Set this option to 9 inches. The
next option is the V_Direction. Set this to
24. These settings will cause the SoftEditSrf command to
fair the hull over an area from the point selected a distance of
9 inches above and below the point and 24 inches forward and aft
of the point selected. The amount that the hull changes
will be at a maximum at the point and taper out to zero change
at these distances away from the point.
The final option is FixEdges. Set this to
"Yes". This will assure that you don't change
the edges of the surface, no matter how much you modify the
surface. This is not an option when editing control
points, as we just observed. This author finds himself
purposely avoiding control points near the edge of a surface,
unless it's absolutely necessary to move them.
Setting these options is done by clicking on the option,
entering the values as detailed above and pressing enter.
Next, click on a point in the Perspective viewport at
approximately the same location as the location of the control
point you edited, previously. Note that you don't select
control points in this command, only locations. The reason
that we selected the control point we did in the first edit was
because it is less than 9" above the edge of the
surface. This will show that even though the U Distance is
set to 9", the SoftEditSrf command will leave the edge of
the surface alone.
Now, in the Right viewport, drag the cursor approximately the
same distance you moved the control point. Notice how
the Isocurves are displayed and change as you move the
cursor, indicating how much the surface will be changed. When
you get the point where you want it, click and then press enter
to accept the change. The surface will be modified to suit
the second location picked. In this way, you can smooth
out the garboard and have no fear that you will mess up the
edges, which match the keel in the actual model. As Fig. 5
shows, there will also not be the dimple that editing the
control point introduced.
Fig. 5 Garboard after moving the selected
point up 1".
The SoftEditSrf command has a companion SoftEditCrv that
works the same.
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6/5/2010
Perhaps the most
amazing piece of magic programmed into Rhino 4.0 is the History
feature and one of the most invaluable aspects of History to the
marine designer, is the way history works with the Loft command.
The author recognizes that not all practitioners in marine
design subscribe to the Loft command as their first choice in
creating hulls and that’s a shame, because it has so much to
offer. Assuming you
Loft your hulls, this section is for you.
But first, a
demonstration of a related topic that will usher in the actual
lofting. Download
and open this model..
What you will see is a hull for a trawler that is the
subject of a tutorial in the series, “Modeling
in Rhinoceros for Marine Designers”.
Along with this hull are a baseline and a series of
station lines. Click
the “Record History” item on the status bar as shown below
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Record
History
Then, in the Front
viewport, issue the “Project” command, select all the
station lines and then select the hull onto which to project the
station lines. “Nothing
amazing about this”, you say?
Right you are, but now for the magic.
In the Front viewport select the forward station line,
either above or below the hull, so that you don’t grab the
actual station on the hull.
Now, move it
forward or aft, while watching the Right viewport (body plan).
Notice that the section changes each time the station
line comes to rest. With
this feature, you can move a couple of sections in close,
“tweak” the hull in the area of those sections and see,
almost real-time the effect your tweaking has on the sections.
Now, set the
layer, “Loft” current and turn off all other layers.
What you will see is a copy of the sections from the
previous exercise. These
curves have been rebuilt, since the project command gave you a
very poor set of Loft candidates.
They’ve pretty closely mimicked the original curves,
but they are a lot “cleaner”.
Click the “Record History” tab in the status
bar and loft these curves.
Since they were all rebuilt at the same time, you can
just window them and issue the Loft command.
Make certain, however that you select the “Normal”
style for the loft.
Again, the results
are less than spectacular. You
just have a hull that doesn’t even go all the way to the bow.
However, there is magic built into this hull, as well.
If you turn on the control points of any of the curves
and move any of the control points, you will note that the hull
changes based on your movement of the control point.
It’s as if the curve’s control points were the
hull’s control points.
If you’ve ever wished that you could move station
points to fair your hull, here is your chance.
As you can see from the following illustration the points
being edited are those of the station curve, not those of the
hull.
Loft
with history
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5/30/10
A question from one of my students in the Proboat
Course prompted this week's tip. It's all about
using curves from your Rhino model in AutoCAD or any other drafting
program that Rhino exports to (usually through the use of DXF
files). It's really pretty simple, but a few pointers will help
you get the geometry that you are looking for. First, a little
background on the specifics. Most of the process of exporting
geometry is a matter of accepting the defaults in the dialogs, however
two options bear a little discussion. These are Polylines and
Splines.
Polylines
Polylines are a series of connected lines and arcs, which
are treated as a single object when selecting for operations
such as trimming, extending, offsetting, etc. Their
chief advantage in AutoCAD is that they can be joined
together. If, for example, if you want your profile to
be a single curve, which can be used for a hatch boundary, you
would use polylines to define the boundary. Note: this
is not to say that you can't use splines as AutoCAD hatch
boundaries. It's just one example of how it might be
handier to be able to join your curves, which Polylines do
quite readily.
Their principle disadvantage is the fact that they are
faceted, which means for a very sharp curve, you need hundreds
of little segments to approximate a curve, whereas for soft
curves, very few vertices are needed. The difficulty is
in finding a good compromise, since all Polylines will be
output based on the same parameters.
Splines
Splines behave in AutoCAD, very much as they do in Rhino.
They are defined by control points and can be freely edited by
manipulating one or two of these control points, vs. the many more
vertices needed to edit Polylines. The chief advantage of
Splines is the fact that they are made up of so few points. Even
though they can be edited in AutoCAD, it is highly recommended that
you get your Splines fair in Rhino before you export them, since the
editing tools in Rhino are so much more powerful. However, if
you find you need to "fudge" your curves a little, it is
much easier with a spline than with a Polyline.
The principle disadvantage to splines is that they cannot be easily
joined. In fact, this author has never successfully joined two
splines in AutoCAD, even though the option presents itself.
Preparing Geometry for Export
Now that the groundwork has been laid, to export your
geometry, you must first make a 2D drawing of the 3D
geometry. To do this, select everything that you want to
export and issue the Make2D command. You can shorten
this command to "Ma" since no other Rhino command
begins with these two letters. However, if you've
created your own aliases and one of them begins with these
letters, then all bets are off.
When you issue the command to make your 3D geometry into a
2D drawing,, the following dialog appears.
In it, you can select to make a 2d drawing of
the selected geometry in
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The geometry as it appears current view,
exclusively
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The geometry as it appears in the current
construction plane (cPlane)
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The geometry as it appears in the three
basic orthographic views plus the perspective view as it is
presently visible on your screen (4 View, either USA or
Europe, depending on which orthographic projection scheme
you prefer)
Also note that you can specify whether to
include hidden lines and tangent edges and whether or not
to maintain source layers. Since the "Maintain source
layers" checkbox is checked in the figure above, the
drop-down listboxes where you can specify layers are grayed
out. You might prefer to use the dropdown listboxes, since
when you use source layers, you will get curves on layers that
are not already included in your Rhino Model. For
instance, let's say you have curves (on layer "2-d
Curves"), hidden edges and tangent edges (on layer
"Hull"). The layers that will be created in the
output will be as follows:
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Hull-Vislble
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Hull-Visible Tangent
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Hull-Hidden Tangent
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Hull-Hidden
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Hull-Annotation
For some reason the curves will be created with
no layer specified, even though they are on layer, 2-d curves in
the model. Anyway, as you can see, you will be presented
with a lot of extra layers, which will more than likely need to
be purged as soon as you've exported your geometry to AutoCAD
and deleted it from Rhino.
Exporting the Geometry
Once you have created the 2D geometry from your
model and have it ready for export, select File > Export
Selected from the menu. If you haven't already done so,
select the curves you want in your AutoCAD drawing and press
enter. Hint: The author prefers to use Make2D and
immediately select Export Selected while the geometry is
still selected.
You will be presented with the following dialog:
Here, you will specify how to export your
geometry. If you will recall, the choice between Polylines
and Splines was discussed earlier. It is here that you
will be presented with this choice, along with many
others. Since you are probably only exporting curves into
AutoCAD most of the other choices will be of no
consequence. However, in the interest of being thorough,
the dialogs are presented, anyway. First, in the dialog
above, select a scheme from the "Export Scheme" drop
down listbox, then click "Edit Schemes". You
will see the following dialog, which has two tabs
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| General tab |
Curves tab |
In the curves tab, a little explanation is in
order. If your selected geometry contains both Polylines
and Splines, you can export each in a different format.
For instance, you can export your Polylines as either Polylines
or as Splines. Likewise, you can export your Splines as
either Splines or as Polylines. If you select Polylines
for your Splines, then you will be asked to specify how
"busy" you want your Polylines to be.
Let's say you are generating a profile and the
sheer is a very "soft" curve (without much change in Z
over its length). Also, let's assume your forefoot is a
very "hard" curve. The values you select for
"Maximum angle" and "Chord height" will
affect how many vertices you will get. It can be readily
appreciated that the forefoot will probably have too few points,
if you make your selection based on the sheer, since the gentle
curvature of the sheer demands far fewer points than the
forefoot. This is the rub with Polylines.
It is for this reason that this author prefers
Splines in all but a rare few cases, since Rhino already deals
with the curves as Splines and can readily communicate the
necessary points to AutoCAD through the DXF file. However,
if you are determined to use Polylines, you'll need to specify a
small enough Maximum angle to make the forefoot look like a
smooth curve and the sheer will just have to suffer with
far too many points.
The angle referred to above is the angle between
two segments of the Polyline. When Rhino begins creating
the Polyline, it starts at the end of the curve known as the
start and creates the first segment based on the value in the
"Chord height" field. When it creates the next
segment, it not only satisfies the "Chord
height" field, but also the angle in the "Maximum
angle" field. The following should clarify this
paragraph a little.
The values in these fields also tell Rhino how
many control points you want in your AutoCAD Splines. When
you've decided on the values for Chord height and Maximum angle,
click the "SaveAs" button to create a new Scheme or
simply save the values in the currently selected scheme and you
will return to the previous dialog. When you click OK in
that dialog, you will be able to specify the name of the file to
create. If you are going to AutoCAD you can create a
.DWG file. If you are going to some other software, your
choice will probably be a DXF file.
Conclusion
From here, what you do with the geometry is an
AutoCAD issue, but I hope I've gotten you through the process
successfully and you can take it from here. This tip is
similar to the tips presented in the Proboat
Course and in the tutorials in
Modeling in Rhinoceros for Marine Designers and Non-modeling
Tutorials for Marine Designers, available on this
site.
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5/24/10
A frequently asked question about working in Rhino is, “How do I get a paper drawing into Rhino?” The answer lies in the use of the Background Bitmap feature. To utilize this feature, first scan your paper drawing so that you have a .jpg, .bmp, .tif or other bitmap. Create a separate bitmap file for each view of the boat. Adobe .pdf files are not usable for this feature. Don’t be too concerned about getting the scan to any particular scale or even to be perfectly aligned. We’ll get to that later. Just make sure there is a
horizontal or vertical line in the paper drawing of a “known” distance.
Next, let’s assume you have a Body Plan that you want to place in your model (the same principles apply to digitizing profiles and plan views). Maximize the Right viewport and issue the “Background Bitmap” command. This can be shortened to “Ba”, since there are no other commands that begin with “Ba”, so Rhino understands these two letters to mean “Background Bitmap” (of course, all bets are off if you have mapped an Alias to the letters “Ba”). You are using the Right viewport for this example, in order to “stand the sections up”. If you were doing the profile, you would use the Front viewport and the plan would be digitized in the Top viewport. When the command is issued, you should see the following prompt:
Choose background bitmap option ( Align Extract Grayscale=Yes
Filter=No Move Place
Refresh Remove Scale Visible=Yes ):
At this prompt, you will note a long list of options. One of them is
“Place” (highlighted above), which is what you want. When you click the “Place” option or type “P” (since that’s the letter that is underlined) a dialog will open and allow you to browse for your bitmap. Select the proper file and you will be returned to the model and asked to pick two opposing corners for the bitmap. Where you pick does not matter, since the background bitmap will invariably not be to scale.
Once you have placed the bitmap, it’s time to make use of that line of “known” distance. Over the top of the bitmap, draw a line that exactly covers the line of known distance (matches its slope), but is the actual length. Say, for instance, it is a baseline and there are two points on it that are 7 feet apart (for instance, centerline and the 7’-0” buttock). Draw a line that exactly covers the baseline on your scan (ie matches the slope of the baseline) and extends from one of the two “known” points (centerline, for instance) on the scan to a point 7 actual feet away
Now, re-issue the Background Bitmap command and select the Align option. Intuitively, you would assume that this command would allow you to rotate the Background Bitmap, but you would be wrong. It only allows you to resize it. Once you have selected the Align option, pick at the centerline end of your curve that covers the baseline. Next, pick a point on the baseline at the intersection with the 7’-0” buttock. Then, go back and pick the centerline end of the baseline again and, finally pick the opposite end of your 7’-0” long line. Your bitmap is now to scale. . In Figure 17, note the dots indicating the picks in the order to make them (centerline, 7’-0” buttock, centerline, outboard end of 7’-0” long line).
Figure 17 Digitizing a Body Plan
Once you have the actual scale established, press Enter to dismiss the Background Bitmap command. Now, using InterpCrv, sketch over each of the sections in the Background Bitmap. During the sketching, you can zoom in to get the best possible view, using the mouse wheel. Also, make sure you create a line on the sketch that represents a horizontal line in the bitmap (the Baseline would be a good choice). You will need this shortly to compensate for the fact that the scan was not exactly horizontal. Although it is not necessary, it is a good idea to digitize the Centerline, also.
When you think you have the entire Body Plan sketched, issue the BackgroundBitmap command again and click on the “Visible” option to turn the bitmap off, temporarily. Inspect your work to make sure it is complete and that you will have no further need of the bitmap. If you need to do further sketching, turn the bitmap back on (the Visibility option is a toggle) and complete your Body Plan.
Once the Body Plan is complete, delete the Background Bitmap, using the Remove option of the BackgroundBitmap command. Now, issue the Rotate command. Select your entire Body Plan, including the Baseline or other line that you drew previously to represent a horizontal line. If you digitized the centerline, be sure to select that, too. At the prompt for a center of rotation, select one end of the “horizontal” line. At the next prompt, select any point along the “horizontal” line. Finally, with Ortho turned on, select a point
beyond the end of the horizontal line (in order to avoid snapping to the “horizontal” line). This last pick will cause everything you selected to rotate so that the “horizontal” line becomes, indeed, horizontal.
One final step is to move everything from the intersection of Baseline and Centerline to the point “0,0,0”.
Proceed as above to digitize the profile and plan view and you can use the three views in concert to create a 3D model of the 2D lines drawing.
Note: this tip is a taste of
the goodies available in the newest tutorial from BaseLine Technology
- Non
modeling Tutorials for Marine Designers.
5/17/10
When dimensioning in Rhino, it is often
necessary to create text either before or after the
dimension. A good example is a dimension that
repeats itself. Instead of dimensioning each of the
several dimensions, individually, create one Dimension and
label it "(typ)". For example, 2'-0"
(typ). Instead of creating the Dimension and then
creating a text object after or before the dimension text,
try the following.
- Create the Dimension
- Double-click the Dimension
- What will appear is an empty edit control with two
symbols ("<>"). These symbols
tell Rhino to calculate the distance between the two
points you clicked when creating the Dimension.
- In this case, since you will be creating a suffix,
place the cursor after the second symbol and type
"(typ)". The edit should resemble the
following illustration. Now, click with
outside the edit control. This causes the suffix
to be added to the Dimension.
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Pretty simple, but now how about when you need to do this
several times (or maybe, hundreds of times). I had
such a situation, when lofting a wooden boat. I had
to do a series of Dimensions, all of which needed to be
preceded by the word, "Bevel ", as in 'Bevel
1/2" '. There were dozens of frames, each with
as many as 10 bevel Dimensions.
To accomplish this, I used the following procedure:
- Create all the Dimensions
- Pre-elect the ones that need the prefix
- In the Rhino Options dialog, drop down the list at
the top that currently says, "Object".
The other choice will be, "Dimension".
Select this choice. Your dialog should resemble
the following illustration.
- In the resulting dialog, the symbols,
"<>" may be replaced by
"(varies)" if any previous editing has been
done. If you find this and don't want to lose
the previous editing, <ctrl><click> the
Dimensions that have the editing. When the
Properties dialog shows "<>" place the
cursor ahead of the first symbol and enter the
"Bevel ". Don't forget the space,
following the "l".
- When you move the cursor out of the edit field, all
the Dimensions selected will assume the value you
entered, but will still reflect the measured dimension
value.
- Note that in the following figure, the
"<varies>" simply means that the value
represented by the "<>" symbols"
is not the same for all the selected Dimensions.
This will have no effect on your edits.
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| If you do enough drafting in Rhino, you
will eventually need these techniques. If you found
this tip helpful or if you have anything you'd like to add
to it, drop by the
forums and let us know. This tip
along with many others are part of the Drafting tutorial
included in the Non-modeling
Tutorials for Marine Designers tutorial
suite.
Up next: Digitizing
a paper drawing in Rhino.
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