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.

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. LineSketchup tutorialtool : [Length]
  2. RectangleSketchup tutorialtool : [Wide, Length]
  3. CircleSketchup tutorialtool: [Sides] [Radius]
  4. PolygonSketchup tutorialtool : [Sides] [Radius]
  5. ArcSketchup tutorialtool; [Sides] [Radius] [Bulge]
  6. FreehandSketchup tutorialtool: None
  7. Tape MeasureSketchup tutorialtool  : [Length]
  8. ProtractorSketchup tutorialtool : [Angle]
  9. ScaleSketchup tutorialtool  [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 Sketchup tutorial 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 ToolSketchup tutorial
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 ScaleSketchup tutorialtool 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.
Sketchup tutorialTo 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 ReferenceSketchup tutorial
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.

Sketchup tutorial
 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.

Sketchup tutorial
 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 Sketchup tutorialmaking 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 MeasureSketchup tutorialtool or  ProtractorSketchup tutorialtool. 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.

Sketchup tutorial
 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 ProtractorSketchup tutorialtool 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.

Sketchup tutorial
 Parallel to one of the Main Axes
When we want to make a  straight line with the LineSketchup tutorialtool, 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
Sketchup tutorial
 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.
Sketchup tutorial
  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 LineSketchup tutorialtool. 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.
Sketchup tutorial
 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
Sketchup tutorial
 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....)