Descriptive Geometry

About Descriptive Geometry

Descriptive geometry deals with physical space, the kind that you have been used to since birth. Things you can see around you have geometry; and even things that you cannot do so too. All these things concern geometric objects almost always in relationship—that is, next to, above, below, intersecting with, occluding, hidden by and so on—to one another that sometimes requires us to make sense of it all—in other words, when we try to solve geometric problems albeit in architecture, engineering, or the sciences. In fact, descriptive geometry has proved itself to be practically useful; it has been one of the most important factors in the design of scientific apparatus, engineering systems and architectural structures.

Descriptive geometry started with Gaspard Monge (1746-1818). He discovered (invented!?) the principles at the tender age of 18, working as a military engineer on the design of fortifications, which were made of stones accurately cut to fit one onto another so that a wall or turret so constructed was self-supporting and strong enough to withstand bombardment. Monge’s descriptive geometry system was declared classified and a military secret and it was not until many years later around 1790s (when Monge was a Professor at the Beaux Arts) that it became a part of French engineering and architectural education and then adopted virtually universally.

Descriptive geometry is constructive—that is, one uses conventional mechanical drawing tools: namely, compass, ruler, protractor, divider, triangles etc to construct solutions to geometric problems.

Descriptive geometry deals with manually solving problems in three-dimensional geometry through working with two-dimensional planes using these basic mechanical tools. This course is mainly about the techniques of solving three-dimensional geometry problems manually.

Compass, divider and ruler 19-th century,
Museum of Islamic Art, Doha, Qatar

About the course

The course starts off with a gentle introduction to some practical constructions just to get a sense of what one can accomplish using mechanical tools before going into details of orthographic projections and culminating in some useful applications such as casting shades and shadows and the intersection of surfaces, and perhaps even, the development of surfaces.

Topics include:

Practical methods in 2-Dimensional Geometry —Some examples—
      Measurements: length and area
      Trisecting an angle using straight-edges and a compass
      Drawing a line between two far points using a short ruler
      Rotating a figure through an angle using just a ruler
      Constructing conic sections

Basic Concepts of 3-Dimensional Descriptive Geometry
Points; Projection Planes; Orthographic Projection; Views; Auxiliary Views

Lines in 3-Dimensional Geometry
Intersecting lines; Skewed lines; Point view of a line; Parallel lines; Perpendicular lines;
True Length of a line; Axonometric views

Planes in 3-Dimensional Geometry
Representation; Points and lines on a plane; Edge View of a plane; Normal view of a plane;
Dip of a plane;

3-Dimensional Spatial Relations of Lines
Examples—line parallel to plane; distances between lines, between planes;

Intersections
Piercing point of line and plane; line of intersection; dihedral angle; visibility;

Rotations in 3-Dimensional Space
Rotating a point about a line, a line about a line, a plane about a line; dihedral angle by rotation

Location of points and tangent planes on Solids and Surfaces
Basic techniques for locating points, piercing points, and tangent planes for common solids—
examples—prisms, pyramid, cone, cylinder, sphere, and possibly oblique solids

Shades and shadows
Based on parallel rays of light

Intersection of geometric surfaces and solids
Of more value to engineers than to architects—
though problems such as the intersection of roof geometry might be of value

Development of surfaces
Planar unfolding of common solids, and solids with warped surfaces (useful for sheet metal work)

Axonometric and Perspective Projections
Based on orthographic projections – method of vanishing points

Topics in the unshaded boxes—namely, the first ten and the last—will be covered in this course; development of surfaces will only be covered if time permits. Topics in boxes 2-10 constitute the bulk of descriptive geometry. The first topic gives a tasty morsel of what constructive geometry is all about. Perspective projections are much more ably and expertly covered in Professor Cooper’s drawing classes.

About grading

Let me frank, I dislike grades. They make some people feel very good about themselves and they make others feel less good. Having said that, they are a necessary evil. The university demands it. Maybe, your parents demand it. And perhaps, some of you even demand it.

Grades don’t often say much about you other than if you are smart and you don’t get a good grade, then you simply didn’t make the effort. Certainly at this university

Learning should be exciting, fulfilling and thoroughly enjoyable. In other words, make an effort. That’s what my attempt at grading reflects.

Grades are based on the following scale.

A	90-100	Excellent
B	80-90	Good
C	70-80	Fair
D	60-70	Pass
R	< 60	If you are a freshman in Architecture, you’ll have to retake this course.

Assignments (60%) + Midterm (12%) + Final (24%) + In-class Participation (4%)

Grades are normally based on assignments, recitations, (closed-book) mid-term and final exams.
As this is the first time I am teaching this course in Qatar I may make some adjustments. Questions will mainly require a geometric construction. It will have to be correct and it will have to be clean. All questions will require a geometric construction. It will have to be correct and it will have to be clean.

If you show up for the assignments, you can get a maximum of 60% (perhaps a bit more as some assignments may contain bonus questions, which are worth extra percentage points). If you show up for the mid-term, you can get a maximum of another 12%. If you show up for the final, you can get a maximum of a further 24%. There is 4% given by the TAs for performance in the recitations.

That is, if you ace the assignments, the best you can get is a D. If you also ace the mid-term, you can get a C. If you also ace the final, you will ace the course. So, show up.

I do not grade on a curve. If you all get A’s, that is wonderful. If you all get R’s, that’s just the way it is. BUT … if you make an effort — it might just push your grade slightly upwards.

Privacy rules

I follow the Buckley Amendment or FERPA rules, which means I hand back your assignments to you and only you in person in class, or in my office. Do not expect me to return your assignments to your classmates. I neither discuss your work with them nor theirs with you.

I also do not publicly post assignment scores or grades.

Late Assignments

Assignments will be accepted late up to 48 hours after the deadline. I normally apply a penalty of 1 point per problem per 12 hours. In addition to the physical copy, late assignments should be scanned and submitted via blackboard for timestamp purposes.

About a textbook and anything else

Textbook — I have prepared a course text, which will be placed on the blackboard. I use several books as my sources.

Mechanical Drawing Equipment — You will need a portable drawing board, compass, triangles, ruler, protractor, pencils, and erasers, all reasonably priced and available in the university shop(?). I will endeavor to obtain these for you. You will be expected to draw in class, especially during the assignment. Generally, figure on A4 size paper for the assignments. I may require you to deal with A3 size paper for the exams.

About the course duration

This is something I will find out. Typically mid-term and final exams are arranged outside class hours during exam week usually about two hours long each. There are about 14 weeks 25 lectures in all. There are 6 assignments, approximately one every two weeks.

Office hours

I do not normally have office hours. As I teach on Sundays and Tuesdays you should be able to knock on my door on Mondays and normally catch me. Otherwise, email me, if it is absolutely necessary.

Recitations

Past experience has shown that students benefit from recitation sessions. I will have to figure out how to incorporate this into your course schedule.

About attendance

I don’t take attendance, but the TAs may.
However, I am banning any open laptop during class – no email, no skypeing, no social networking during lectures.

About students with special needs

For whatever legitimate reasons accepted by this university, I’ll do my best if it is within my power to help you. If not, you must contact your primary academic advisor in your home department.