Tool time: Circle and Arc Tool

Circle Tool and Arc Tool

We previously used the Arctool to make convex/concave lines to create profile for the ceiling molding. However, up till the the end of this Sketchup tutorial, we are not going to use the Circletool. Since this is a rather fundamental tool, we are going to  have a rather thorough discussion regarding the Circle tool at this section. 

There are also two other tools at the 'Drawing toolbar', namely Polygontool and Freehandtool. There is nothing special about the Polygon tool since its usage is largely similar with the Rectangletool.  Polygon tool will create a regular Polygon entities, with 3 or more equal sides. This tool provides us with option to enter the number of edges to create and the radius of the polygon. Freehand tool is somewhat similar with Linetool. Freehand tool is used to draw irregular hand-drawn lines which are comprised of multiple line segments that are connected together. When the the starting and ending points of the lines coincide, a face will be created.

I have no plan to discuss the Polygon, and Freehand tools. Their usage are rather simple. Besides, I hardly use these tools. In the contrary, Arc and Circle tools are used quite frequently and some aspects should be known to optimally use the tools, so I will explain these two tools in a more detail fashion in this section.

Getting to know Circle and Arc Tool

SketchUp can only recognize straight lines and faces (flat surface). Hardly there is any object that consists of only one straight line. No wonder, in SketchUp, there is no function or command to thicken or to color one particular line.

Circles and Arches are basically just a number of straight lines of the same length stitched together to appear like a circle or an arc. Each line is called as a segment. The more number of segments created, the smoother the circle or the arc will appear. However, it will affect the file size and therefore heavier burden to the computer processor.

Circle Tool

Below is the Entity info window when the outline of a circle is selected (just the outline, not including the face)

Right after the Circletool is activated, we are given the opportunity to change the number of its sides (segments) by typing in the desired number and then press [Enter]. Initially, the number of segment provided by SketchUp is the default circle's segments (24), or the last value that we set for the this tool. The circle radius is determined after we choose its center point using mouse click and move out the cursor or by typing in a length value followed by [Enter].

The strictest work flow of a circle creation is:

1. Find a plane that will be used as the reference for the new circle orientation. You can use one the main axes, any existing face, or create a temporary face for the reference.
2. Determine a point in the model that will be the center point, or create a guide(s) using Tape Measuretool and/or the Protractortool to obtain a precise location.
3. Click the Circletool and, if necessary, change the number of segments to your liking.
4. Move the cursor over the area to be used as the reference (as in point 'a'). If the circle plane is different than the referenced plane, press and hold [Shift] key to lock the orientation.
5. Click at the point you want as the center point of the circle (point b) and,
6. Move the cursor away to any direction, then click after the circle radius seems appropriate or type in any number using the keyboard then press [Enter] to set the radius precisely.

Step (f) can be made at any time using the entity info window as shown previously. Step (c) can only be done if the circle has not been converted into 3-dimensional shape. For the rest of the steps, editing can be done using the Move/Copytool. Note that point (a) must be done correctly from the beginning, since changing the orientation sometimes is not as simple as creating a new circle from scratch.

Determining the plane where the circle will be created

Once we select the Circletool, before clicking the mouse to determine the position of the circle's center point , we must first determine on what plane the circle will reside, or which plane will be used as a reference. If we use the standard ISOview and there is no other object that can be used as a reference, then the circle can only be made on the plane perpendicular to the Blue Axis. Reference to any other axis can only be done on the appropriate camera angle as shown in the animation.

Tip & Trick

Determining reference for the rotation plane If the new circle will not be placed at any of the existing geometry (existing faces) we need to find a reference for the rotation plane of the circle. The same principle applies to the Polygontool, Rotatetool and Protractortool. Any of existing faces and one of the main axes can be used as the reference.

Normally, a circle is made on a face of an existing object. So just need to click at the face and the circle orientation will automatically follow the referenced face. Otherwise you need to select a particular face or one of the main axes as a reference and then lock the face orientation by pressing and holding the [Shift] key and then choose any position to be the center point of the circle.

Animation below shows, when the standard ISOview is selected and no other object can be used as a reference, the orientation of a new circle can only be set to the blue axis. We can change the view as shown at the end of the animation, or create a temporary object that can be used as references. As usual, after we obtain an orientation reference, we press and hold [Shift] key until after we click a certain point to set it as the center point of the new circle.

Creating various circles with different orientation.

What about Oval shapes?

SketchUp does not provide us with a special tool to create an oval or ellipse shape. To create an oval shape, we first create a circle, then reduce or enlarge one or both of the diameters to get the desired oval shape.

To resize a circle diameter, we use Scaletool available on the Edit toolbar. Click once on the circle ,then select the Scale tool so that a yellow bounding box with eight green grips is displayed around the circle. Click one of the grips in the middle of one of the bounding box edges (not one of the corner grips), and then pull the grip out or in until the desired oval shape is achieved.

Tip & Trick

Scale Tool Scale tool is used to resize an existing object in the model by dragging one on the available sliding points. There are two modes of scaling using the measurement box: By specifying the sizing coefficient (default) or by determining the final dimensions of the altered aspect. For the second mode, we must add a value and its notation before pressing enter (such as 5' 3" for five feet and three inches).

To obtain an accurate shape/size of the oval, it is better to type in the desired final value of diameter along with its unit notation (e.g. 150 cm) using the keyboard and then press [Enter]. Then the diameter we resize will have the final dimensions of 150 cm. Or, enter a value (e.g. 0.5) and press [Enter] then the new size of the diameter will be exactly half of the original.

Arc Tool

The illustration below shows an arc and a dimension information along with the Entity info of the arc. .

Radius information indicates the radius of the circle that forms the arc. As we know, an arc is a segment of the circumference of a circle.

In contrast to the circle tool, the information on the Entity Info window of an arc is different with the parameters available during its creation (as displayed in the measurement box). Bulge is not available in the entity info window and scaling will not always result as expected. This indicates that most of the time it is easier to create a new arc than editing an existing one using the entity info. Normally we first prepare two lines that will hold the starting and ending points of the arc, then determining the curve between the two lines.

The strictest work flow of an Arc creation is:

1. Decide which line end(s) to start or to end the new arc.
2. Activate the Arctool and, if necessary, change the number of segments of  using the Measurement box.
3. Click on the first point and click on the second point to set the beginning and the end of the curved line (both ends of the green line at the above picture), or enter its length using the keyboard and press [Enter]
4. Move the mouse cursor towards any position between the two points and click or input the height of the protrusion (the red line at the above image), or type in the bulge value through the keyboard and press [Enter].

Step (b) can be done at any time using the Entity info window as shown above. As you can see the information on the Entity info window, one aspect that can be changed directly is the segments (point b). The other aspect that can also be changed is the radius of the arc (not included in the Measurement box). However, we usually are concerned more with how to make a seamless curve to a line/curve or a corner, not with the exact size of the arc itself.

Creating a perfect connection between an arc with a line or another arc.

Connection of an arc to a line or to another arch will look seamless if  the two objects share a common characteristic.

The Cyan and magentaa line d on the second picture). The arc connection would be perfect if b (and c) is the radius of each curve and b perpendicular to the line a. For the second image, c is perpendicular to the line d.

Colored curves in the picture are arcs with a certain radius. These curvature form smooth curves that the arc is a continuation of the red line (or that connects line Similarly, between two curves / arches. An arc (the black arc) can connect with another arc (the cyan act) seamlessly when AC is a straight line, and AB and BC is the radius of each corresponding curve. The illustration indicates that the cyan arc starts at the end point of the black arc AND the radius of the cyan arc is in line with the radius of the black arc.

The connection point between the curve and another object is referred to as a tangent to the curve. You don't to need to even remember this, because SketchUp will provide color information when the connection is perfect with the inference "Tangent at Vertex." cyan inference indicates the arch merge perfectly to a line or to another curve, and magenta indicates that arch fits seamlessly with two lines and/or other arch.

To invoke the Magenta inference, the starting and ending points of the curve should form an isosceles triangle with the peak lies between these two points. When isosceles is achieved, the inference color will turn into magenta as seen in the animation below.

(Note: Line b, c and AC in the above illustrations are provided for explanation purpose only. If any of these lines does exist, no inference information will appear)

Creating curves with a smooth continuation from another curve or line(s)

In another part of this General section, we will learn to create three-dimensional shapes based on circles and arches, e.i. to create balls, rings, tires and so forth.

Keep on Sketching ...

Harrynov

Improving Model Accurary

.. accurate "no sweat" modeling ..

SketchUp is not intended for engineering purposes that demand for high accuracy modeling. However, it is accurate enough to make 3D models larger than a few centimeters. For the purposes of architecture modeling, of course, SketchUp's level of accuracy is sufficient.

Warning

Non Planar Face SketchUp automatically creates a face when a set of lines make a closed loop and are all in the same plane. However, Sketchup also makes a little approximation that even when some of the lines are a little off (not exactly in one plane), a face will still be created. This can be difficult when we try to do push & pull on the face. The results can be messy or not possible at all. Using inferences will avoid such problem.

There are three aspects that determine whether models you create are accurate: 

1. Accuracy in measurements
2. Accuracy of object positions 
3. Accuracy of object slopes.

SketchUp provides us with various information and techniques in the form of reference to another object and  inference from existing objects or axis. This will facilitate the making of an accurate model without always having to specifically enter dimensions and slopes of objects being created/edited.

Accuracy in measurements

Measurement Box

The surest way to make accurate dimensions and slopes is using Measurement Box. Almost every object has its own set of parameters depending on the current tools we choose (context sensitive). Here are some examples:

Tip & Trick

Measurement Box As indicated in "A Fresh Start", Measurement Box is one the three elements of SketchUp. Notice that there is no blinking cursor to make input or to edit value(s) in the input field. There no other way to enter parameter(s) other than typing blindly using the keyboard.

1. Linetool : [Length]
2. Rectangletool : [Wide, Length]
3. Circletool: [Sides] [Radius]
4. Polygontool : [Sides] [Radius]
5. Arctool; [Sides] [Radius] [Bulge]
6. Freehandtool: None
7. Tape Measuretool  : [Length]
   
8. Protractortool : [Angle]
9. Scaletool  [multiplier], or with the unit symbol, [Desired dimension].

[Bracket] indicates that you have to press [Enter] after each entry.

Measurement Box is active only during an object creation, until we do another mouse operation. As long as we have not done any other mouse operation, we can continue changing the last entered parameter through the keyboard. The size (or slope) of the object will automatically change every time [Enter] key is pressed.

Scale Tool

Tip & Trick

Scale Tool Scale tool is used to change the size of existing objects in the model by dragging one on the available sliding points. Combining Scale tool with [Ctrl] key will scale object from its geometry's center point.  Combination of Scale tool with [Shift] key will scale the object with some uniformity.

Measurement Box can be used only during objects creation. For existing objects, change in size can only be made by changing object directly. One of the methods is  by using Scaletool in Edit toolbar.

When an object is selected using the Scale tool, there will be a bounding box with several scaling points that can be selected and dragged by the mouse. There are 24 scaling points for 3-dimensional objects, and 8 points for 2-dimensional objects. as seen in the figure below.
To get an accurate scaling, Scale tool must also be accompanied by entering parameters through the Measurement box. There are two ways to use Measurement Box with the scaling tool. First, by entering a value as the scaling factor, second by inserting a value complete with dimensional unit(for example: 125cm) in order determine to final dimension of the aspect being scaled.

Editing using Reference

I am not a fan of Scale tool because sometimes some aspects are not completely controllable so that the result sometimes would not be as expected. I prefer using one of the Edit tools and cutting and slicing the object so that elements of an object can be individually changed.

Referencing is the next best thing in SketchUp after Push/Pull. By using references, we can make an object as accurate as possible (dimension, location, slopes) and use the object as a reference to make or to edit another object. This saves a lot of time. 
Therefore, my work flow to create objects accurately is: Create initial object(s) and maintain its accuracy using Measurement box, and reference the object(s)  during creating/editing of subsequent objects.

Reference to Another Object

The most effective and efficient way to edit an object is by referencing its change to an existing object. If the referenced object is accurate, then the edited object will also be accurate.

Push/Pull by referring to other object

When pushing/pulling a face  of an object, we drag it to a new position to lengthen/ shorten its overall size.
If we move the cursor to a face or any other point in another object to use it as reference, the face being edited will be at the the same plane with the referenced face/point. Again, this means that if the reference is accurate, then the change we are doing to the object will also be accurate. This is a time saver since we don't need type in any value whatsoever to make it accurate.

Redoing Last Operation to Another Object

Sketchup has the ability to apply one operation to separate objects with identical result. This is done by double-clicking other object(s) after an operation is completed with the initial object . The editing operation can be repeated as long as we do not select any other tool.

Redo Operation with Double Clicking

With double clicks, the same operation will be applied to all of the objects.
So if the first editing operation is measured accurately (i.e. using Measurement Box), all other operation will also be accurate
without having to make any entry with the Measurement Box.

The animation shows how we can repeat an OFFSET operation on several face shapes. For each double clicking, another shape with the same contour will be created exactly with the same distance from the original edges. If we specifically entered a certain length with the Measurement Box as the offset distance, then all the new shape will also have the same accurate offset distance. This is how I often do to make walls in SketchUp.

Adding Guides with a Certain Distance from a Known Position.

Another method to ensure accuracy is to add guides in the form of lines or dots to a model to be used as reference in making changes or adding objects. The guide will be positioned a certain distance from a known line/point in the model (i.e. one of the Main Axis).
Guides is created using Tape Measuretool or  Protractortool. Tape Measure tool is used to create a parallel guideline at certain distance from another line, or to create a point at a certain distance from another point. Protractor tool is used to create a guideline with a specific angle to a line, (or two points) that can be used as reference. Guides are usually removed immediately after their use so as not to obstruct your view.

Creating "Guides"

The following animation shows examples how to  add guides using the Tape Measure tool and Protractor tool to an object. Note that when Protractor selected, the cursor changes into an arc /protractor shape. The usage of this tool should also be followed by entries to the Measurement Box to ensure accurate position of the guides.

Accuracy of Object Position

The easiest way to ensure accuracy of any object placement is to put the object in reference to existing object (its midpoint, it's corner, etc). If the referenced object has been positioned accurately than the edited object will also accurate to that position. If there is no object that can be used as a reference, of course, you can always make Guides to place your object on the location of the guide.

Slope and Angle Accuracy.

We could always set every slope(s)/angle(s) of an object using Protractortool as previously discussed. Accurate but not too practical. If you want to create a line that is parallel or perpendicular to another line, it is much faster, yet still accurate,  to utilize SketchUp's Automatic Inference.

Tip & Trick

Automatic Inferencing color By default, Black line indicates no inferencing is detected. Blue, Red, Green indicates that inference is made parallel to one of the main axes. Magenta and Cyan indicates parallelism, tangent or perpendicular with a certain existing line. Note that inferencing behavior is affected by your mouse clicking and hovering. Some can make a certain inference fail to appear.

Intelligently, SketchUp will always try to inform you whether your drawing direction has a unique sloping characteristic (parallel,  perpendicular or and tangent, or even equilateral) to one of the main axes or another nearby line/curve in the model.  Therefore, if you want to make an object which is parallel, perpendicular or tangent to an existing object, or create equilateral triangle, we don't need to use Protractor tool at all. With this automatic inference, 3D modeling can be done easily and quickly, but still be able to maintain accuracy.

Parallel to one of the Main Axes

Most of the time, Main Axes are the main references when adding/editing an object. Therefore, it is advisable to always use them as the axes of your model (most of lines are in the model are aligned with one of these axes). Otherwise, main axes referencing may not as useful.

Parallel to one of the Main Axes

When we want to make a  straight line with the Linetool, Sketchup will automatically indicate whether the line is parallel with one of the existing axis. Black indicates the line does not align with any of the axes. The color will change to the color of the axes it is parallel with.  This is very useful, for example, when we want to make a line perpendicular to the a floor, then we will move the cursor upward until the resulting line turns blue and click at desired position.

Referencing to a line not parallel to any of the axes

In addition to the Main Axis inferencing, we can also obtain inferences from a curve or line that is not parallel to any of  axis

Parallel to another line

Parallel another line

Creating a line parallel to another line is accomplished by clicking the starting point of the new line that we want to make  and then hovering your mouse towards the midpoint of the line will be used as a reference. This will induce inferencing from the line. Next slide the mouse in the direction approximately parallel to referenced line. Continue your line when the color turns into Magenta.

Continuing a sloping line.

Continuance of a sloping line

During model creation, we often need to make shape as a continuance of a sloping objects. For example we want to add eaves to the existing roof. Instead of creating a new object using Rotate tool,  it is far more quicker to create a  line with the same slope with the roof. I.e. by determining the starting point  (end of the sloping line) and then draw a line using Linetool. Move your mouse in the direction that approximately extending the slope and click only when the line turns  Magenta.

Finding other inferences.

Perpendicular to to an edge.

Perpendicular Line

Making a new line perpendicular to another other line is accomplished  simply by clicking at any point in the referenced line as a starting point of the new line and and move the cursor to a direction which is approximately perpendicular to that base line. Click at the destination point only when  the resulting line turns into  Magenta. That indicates that is has a perpendicular characteristic to the starting line.

Tangent and Perpendicular with an Equilateral Triangle

Creating a perfect curve

Automatic Inference will not always provide you with hints regarding the inference made during an operation. I.e.. when you move your mouse too fast. However, the inference color will always appear.

The animation shows the following when we use the Arc tool. The first  Magenta inference indicated that the starting and end point of the curve that will form an equilateral triangle from a point located between the two sides. Once we click that position, we will determine the curvature of the arc we are making. The curve color is  Magenta to indicate that the radius of the circle that forms the curve is formed are tangent at the start and at end of the curve.


(...whew ... I need to brush up my trigonometry know....)


Harrynov