(See related pages)
Visualization is the mental understanding of visual information. For students in engineering and technology, visualization skills can be crucial in understanding the fundamental concepts of technical graphics. The ability to visualize also greatly enhances the speed and accuracy with which drawings can be done, using traditional drafting techniques or the computer. Visualization skills can assist you in building and manipulating a 3-D design in the virtual world of the computer.
|
|
|
VISUALIZATION ABILITIES |
|
|
|
| 5.1 Students will come to your class with truly diverse abilities to mentally create and manipulate graphic imagery (visualization). Either through their life experiences or through innate ability, some students are simply better at visualization than others. This does not mean that those who don't come to your class with strong skills can't be taught many of the skills presented in the text. What it does mean is that it will be worth your while to try to informally assess your students' visualization abilities; either through exercises presented in this chapter, direct observation, or other methods. The ability levels of your students may influence the level of instruction needed to get students to an appropriate level of proficiency. It's important to distinguish between the different types of proficiency necessary in engineering and technical graphics. One possible way of categorizing these proficiencies are as follows: Visualization skills. Being able to mentally create and manipulate graphic imagery and transform this into physical graphic images. Motor skills. Being able to quickly create a sketch or drawing with high quality linework. Rule-based knowledge. Conversant in ANSI standards, drawing conventions, software commands, etc. All of these are important to becoming a successful graphician and some students will have better abilities in some areas than others. Most other texts concentrate on the last two areas but only infer the need for visualization skills. This text has attempted to formalize this need in this chapter. Because of the historic admission of this material, many instructors have developed their own materials for teaching these skills. Since nothing works like success, you should integrate those techniques you have found successful with those presented in this chapter. The material in this chapter does not present 'the right way', it has simply tried to bring together techniques that have been used successfully in the past and place them in a logical conceptual framework. |
|
|
|
THE VISUALIZATION CYCLE |
|
|
|
| 5.2 It is important to emphasize the dynamic qualities of the visualization process. Not only can this dynamic process be taking place solely in one's head, but also between the mind, the eyes, and some physical stimulus such as a drawing or an object. To apply these ideas in a more functional way, have your students experience this feedback loop. If you have already done some sketching exercises (see Chapter 4, Sketching and Text), then ask them to sketch a simple object in pictorial form. Now verbally describe changes you want them to make in their object (e.g. drill a hole through it, chamfer a corner, etc.). Ask them to first mentally imagine this operation and then sketch it. They can also do this completely on their own; have them start with a simple shape and then transform it into a common household object over a series of four or five sketches. |
|
|
|
DESIGN VISUALIZATION |
|
|
|
| 5.3 Some point soon after starting the visualization exercises, tie the visualization process back to the engineering design process. You may want to run a brief brainstorming session designing a product (see the supplemental design problems included in the Graphics Instructor's Library). First as a group and then individually, have them generate a half a dozen or so design concepts for a product. Have them focus on variations in the geometry between the designs. |
|
|
|
SOLID OBJECT FEATURES |
|
|
|
| 5.4 Having physical objects of simple geometric shapes available is a great help in explaining the concepts and conducting exercises in this section. They can be quickly made from wood, foam, clay, paper, etc. |
|
|
|
| 5.4.1 Make sure the students can 'see' the features which define the objects. Some of these features represented on drawings (e.g. edges and faces) have direct correspondence to physical attributes of the object. Other features depicted in a drawing (e.g. limiting elements and center lines) do not have a corresponding physical element. This does not mean that students cannot develop an ability to visualize these elements. Make sure the students begin to develop both a geometric and topological understanding of the objects. That is, if you ask them halve the area of the end face of a square prism, they understand its geometric effect on the side faces. To understand the geometric effect on the side faces, they must also understand the topological connectedness of the faces of the object. What happens when you halve the area of a face on a cube? Do you use the same process to gauge its effect on the faces? Are the same number of faces effected? What happens when you halve the end face of a cylinder? |
|
|
|
VISUALIZATION TECHNIQUES FOR TECHNICAL DRAWINGS |
|
|
|
| 5.5.1 Another important use of planes is as an image plane; a primary component of projection theory. This section can be used in conjunction with the introduction of the principles of projection in Chapters 4, 7, 8, and 9. There are many ways of teaching the concept of projecting an image on a plane though often the most effective method is a direct experiential one. This section presents a number of Practice Exercises incorporating a physical object and an image plane made from clear plastic. If there is time and materials, the best option is to allow the students to do these themselves. You can choose whether you want to, at this time, emphasize the more formal nomenclature of projection theory such as line of sight, parallel versus perspective projection, etc. Probably more important to avoid introducing informal terms for some of these elements that later have to be ignored when more formal terms are introduced. |
|
|
|
| 5.5.2 It is a fairly straightforward progression to move from the manipulation of cutting planes relative to objects to the manipulation of image planes relative to the object. In fact, much as you investigated normal, inclined, and oblique surfaces with cutting planes, the same can be done with the projections on image planes. This is a good opportunity to introduce the concept of foreshortening which occurs anytime a face is not normal to the image plane. You can draw the connection between the direction of rotation of the object or image plane and the dimension which is foreshortened. |
|
|
|
| 5.5.3 There is a very strong connection between the concept of multiple image planes and the interface used in most 3-D modeling software packages (see Chapter 7, 3-D Modeling). In addition, the concept of multiple image planes is also a central component in understanding multiview projection (see Chapter 8, Multiview Drawings). Whether your course incorporates 2-D CAD, 3-D CAD, or neither may affect how you approach the teaching of this section. Like the topic of multiview drawings, understanding the interface to a 3-D modeling system is one of the hardest concepts to grasp. It is worth spending some extra time making sure students have the facility to visualize with this technique. |
|
|
|
| 5.5.4 If you are going to have a 3-D modeling component to your course, you will probably want to discuss its ramifications on viewpoint selection. By demonstration you can show the difficulty of creating a dimetric or trimetric projection by hand compared to doing so on the 3-D modeling system. Emphasize that the traditional views have been developed as standards both for reasons of clarity of information and for ease of generation. Especially when generating pictorial views with a 3-D modeler, emphasize that the viewpoint selected should be based on an evaluation of the features on the object rather than what is the 'default' view chosen by the modeling software. |
|
|
|
OTHER VISUALIZATION TECHNIQUES |
|
|
|
| 5.6 As mentioned earlier, be thinking about exercises that you have used in the past and how they might be integrated into this chapter. Exercises that you have used when teaching multiview projection may be useful in this chapter and exercises in this chapter will certainly be useful later in the course. |
|
|
|
| 5.6.1 Though perspective projection is often not taught in an introductory course, it is the projection technique which comes closest to how we perceive physical objects. If you are having students drawing on image planes it may be important to talk about how the convergence which is perceived is 'removed' in a parallel projection (see discussion of this in the instructional notes in Chapter 4). |
|
|
|
| 5.6.2 Shading is an option available on most 3-D modelers. Shading goes a step beyond hidden line removal in trying to recreate a realistic computer model. If you do use shading, keep in mind that it can also be used illustratively. By shading surfaces different colors, you can highlight inclined surfaces, etc. More detailed information about shading is given in Chapter 20, Technical Data Presentation. |
|
|
|
| 5.6.3 Later in the term, your students may be working with assemblies. Whether these assemblies are being constructed in 2-D or in 3-D, the ability to visualize multiple objects and the occlusion of the farther object behind the nearer one is an important skill. Even if you are using a 3-D modeling system and the hidden line removal is done 'automatically', it is still useful to be able to predict ahead of time how the projection will appear without spending the computer time to calculate which edges and faces are occluded. |
|
|
|
GRAPHICAL ANALYSIS OF ENGINEERING DATA |
|
|
|
| 5.7 This section establishes the context of technical data visualization in the analysis phase of engineering design. Though this section is presented in a fairly abstract way, there are numerous real world examples you can draw on to get this material across. The idea of designing a reactor vessel and exploring the relationship between temperature and pressure is used in figure 4.41. This example could have just as easily been the deflection of steel beams in a roof construction under a prescribed load (civil engineering), vibrations resulting from varying the rotational speed of a compression pump (mechanical engineering), or the change in assembly line output caused by varying the cycle time on a circuit board installation (industrial engineering). |
|
|
|
DATA VISUALIZATION ELEMENTS |
|
|
|
| 5.7.1 This section begins the development of the taxonomy of visualization methods. Figure 2.66 lays out the structure of the taxonomy and the structure of Sections 4.5.2 and 4.5.3. Though engineering students have been working with numbers intensively for years they may, in fact, have had little or no exposure to the terms used to describe data types. Many of these terms are more likely to show up in a statistics text than an engineering text. One of the goals is merging techniques which have been used in the social sciences — and to some degree in the hard sciences — with engineering analysis. Of interest is less the methodology than the data manipulation and visualization techniques. Marks are at the heart of the perceptual basis of data visualization. What largely distinguishes one type of visualization from another is the type of marks it uses. Equally important is the subtle variations that can be applied to the marks by the user. This section and the next two show examples of how marks can be manipulated to more effectively communicate the information in the visualization. Good and bad usage of marks is a great way to demonstrate the power of these perceptual cues. Though independent and dependent variables were alluded to in the first section of the chapter, they are formally introduced here. The design analysis problem in Figure 2.2 is also formalized with a visualization showing the relationship on a independent and dependent variable. The visualization types presented in Section 2.3 are broken down by the number of dependent and independent variables. This was done to assist students in matching visualization techniques with the type of data they are/will be working with. |
|
|
|
VISUALIZATIONS FOR ONE INDEPENDENT VARIABLE |
|
|
|
| 5.7.2 It is noted that graphs, charts, and plots are all common terms for types of visualizations. There is little consistency in how these terms are applied and the chapter tries to stay with the most common usage. This section covers the most common types of visualizations: line and bar graphs. This section also introduces the student to a design theme that goes throughout the chapter: less is more. Test will be — just as with any engineering graphic — what information is being conveyed and are there graphic elements to support each of these pieces of information. There are numerous parallels between the impact of CAD in engineering drawings and the effect of visualization packages on graphs and plots. The section on line graphs introduces the concept of regression lines and error bars. Though a full appreciation of these techniques requires some background in statistics, students can still be introduced to them so they know what they are seeing when they run across examples of them. Quite a few examples of bar graphs are given, in part, because of their popularity and flexibility in presenting different types of data. It is probably worth spending a few minutes making sure the students have a basic understanding of the different types of bar graphs and their appropriate usage. |
|
|
|
VISUALIZATIONS FOR TWO INDEPENDENT VARIABLES |
|
|
|
| 5.7.3 Students are also likely to encounter analytic data with two independent variables. They are also much less likely to attempt visualizing this type of data, not so much because of a lack of tools to do so as a lack of understanding as to how to do so. Multiple line graphs are a very powerful technique and allow the integration of a much higher density of data than a single line graph. One of the biggest pitfalls of this technique is choosing an appropriate encoding technique for the second independent variable representing the different lines on the graph. Remind students that they must keep in mind the different medium in which the visualization will be displayed. Will there be color? How big will the graphic be in relation to the distance it will be seen at? What is the resolution of the medium; will fine detail be lost? As mentioned in the section, time is a popular second independent variable and animation techniques are a powerful method of displaying it. Even if the students do not have the opportunity to explore animation techniques as part of a lab, try developing a demo which compares the static presentation of sequential visualizations and the same data presented as an animation. It is also worth looking at the difference in presenting the sequential visualizations in parallel (i.e. all in a single graphic image) or serially (i.e. as a slide show). Each technique has its own advantages and disadvantages that are worth imparting on the students. 3-D graphs and plots represent the first use of the third dimension in the chapter. This and other perceptual cues such as color and hidden line removal (occlusion) are all important considerations in designing such visualizations. This is an example of a visualization that was rarely used before the advent of computer-based visualization tools. It is now a standard tool in many packages and is very effective when used properly. Area rendering is not very common in engineering but has become a very popular technique in other areas such as medicine and the earth sciences. Images created by medical professionals, such as X-rays and CAT scans, lend themselves to encoding as digital renderings as do the satellite images used by geologists and meteorologists. Much more in-depth information on 2-D image generation and manipulation can be found in many of the references at the end of the chapter. Vector and flow representations are less common than some of the other areas but have considerable potential for application in areas such as aerodynamics and fluid dynamics. |
|
|
|
VIRTUAL REALITY AND VISUALIZATION |
|
|
|
| 5.8 An important concept to get across to students is that 3-D models created on the computer are meant to be virtual models of real world objects. Virtual reality is simply technology that strives to make this model and its surrounding environment as realistic as possible. The two main factors in the success of this experience is the fidelity and responsiveness of the virtual environment. Together, these two factors create a sense of immersion. For most VR systems, immersiveness is achieved with the following features:
A distinction should be drawn between telepresence and VR. Typically, the VR system uses an environment that is by and large synthetic. That is, it is created completely on the computer. Telepresence uses remote video equipment under the user's control to allow someone to experience a real environment that is in a remote location. |
|
|
|
VISUALIZATION USES |
|
|
|
| 5.9 Encourage your students to use the WWW and other sources to find current examples of how visualization techniques are being used to further science, engineering, and technology areas. |