Geodesic Glossary
This is a glossary of geodesic-related terms. For an illustrated and more in-depth collection, you can download the PDF by clicking on the image below. It was prepared by Joe Clinton for one of the early Synergetics Collaborative (SNEC) meetings.
Remember that many of the same geodesic/geometrical concepts have different names, depending on the context. For example, mathematicians generally refer to “faces, edges and vertices of a polyhedron” while a builder, or even some of the geodesic software programs like CADRE Geo, talk about “panels, struts and hubs of a dome”.
One of the terms used by Clinton in the PDF is “tangential angle”, namely 90 minus the axial angle. When you’re in the workshop, the tangential angle is the same as the mitre setting (MS) angle on a compound mitre saw or a radial arm saw.
| Aluminet | Aluminet is a metallized fabric (HDPE or high-density polyethylene) that works like a thermal blanket. Its manufacturer, Polysack, calls it a thermal shade net. When this material is used for example for a greenhouse, it keeps the interior cool in daytime, warm at night. For geodesic dome structures it creates a comfortable space letting in a breeze. |
| Bauersfeld, Walther | (1879 – 1959 ). Bauersfeld completed the first planetarium, known as the Zeiss I and patented by his employer, the Zeiss Optical Company, in 1922. It is credited as the first geodesic structure ever built. |
| Bend angles | Refers to the bend of a strut end. Every strut in a geodesic dome requires a strut to be bent at both ends. The angle is derived from a mathematical formula. |
| Bucky | Affectionate term given to Buckminster Fuller. |
| Bucky ball | Bucky balls are named after Buckminster Fuller who popularized the geodesic dome. Bucky balls shapes are also found in the Carbon 60 molecule. It’s the roundest and most symmetrical large molecule known to man. |
| Chord factor | The ratio of the chord length to the radius of the circumscribing sphere. The mathematical object “chord” of the “geodesic sphere” corresponds to the structural “strut” of the physical “geodesic dome”. A chord is a (straight) line segment joining two points on a curve. |
| Compound angle | Commonly used to describe a wood strut which is cut at an angle on two planes. |
| Conduit | Alternative description of EMT (electrical metallic tubing). |
| Diameter | Officially it’s a straight line segment passing through the center of a figure, especially of a circle or sphere, and terminating at the periphery. In practical terms it describes the width of your geodesic dome, twice the value of the radius of the dome. |
| Dihedral | An angle formed by two planes meeting in a common lineThe two planes themselves are faces of the dihedral angle and their common chord is the common line.To measure the dihedral angle, measure the angle whose vertex is on the chord of the dihedral angle and whose sides are perpendicular to the chord and lie one in each face of the dihedral angle. |
| Elliptical | Egg-shaped: rounded like an egg. |
| EMT | Electrical metallic tubing, or EMT, is more commonly known as conduit. EMT is is made from high-grade rolled steel, and the surface is coated with a clear zinc chromate. The coating helps prevent corrosion in outdoor installations or harsh climatic conditions. EMT is easily cut and bent to fit most any application. |
| ETFE | Ethylene tetrafluoroethylene, ETFE, a fluorine based plastic, designed to have high corrosion resistance and strength over a wide temperature range. ETFE is a polymer, and its systematic name is poly(ethylene-co-tetrafluoroethylene). ETFE has a very high melting temperature, excellent chemical, electrical and high energy radiation resistance properties. ETFE has an approximate tensile strength of 42 N/mm² (6100 psi), with a working temperature range of 89 K to 423 K (-185 °C to 150 °C or -300 °F to 300 °F). The Eden Project in the U.K. has successfully used this product to roof the multiple geodesic domes of the complex using three layers of ETFE and inflating them. They are referred to as pillows. |
| Frequency (of a dome) | The frequency of a dome relates to the number of smaller triangles into which it is subdivided. A high frequency dome has more triangular components and is more smoothly curved and sphere-like. |
| Fuller, R. Buckminster | (1895 – 1983). His most well known accomplishment is the geodesic dome, produced over 300,000 times worldwide. Throughout the course of his life Fuller held 28 patents, authored 28 books, received 47 honorary degrees. |
| Geodesic dome | The term geodesic is from Latin, meaning earth dividing. A geodesic dome is made of a pattern of triangles resulting in a great structural strength while using the least material. Though Buckminster Fuller patented the geodesic dome in 1954, the first person credited for a geodesic dome design is Walter Bauersfeld. |
| Golden ratio | Also called the golden mean, represented by the Greek letter phi, it is one of those mysterious natural numbers. It divides a whole into two parts, one larger, one smaller. The division is not random so that the ratio of the larger to the smaller is perfectly proportioned roughly one to 1/3 to 2/3. Actually, it’s 1.618 033 988 749 894 848 etc. |
| Great Circle | Any plane passing through the center of a sphere, its intersection with the surface of the sphere is a Great Circle and the largest circle on the sphere. All other circles on the sphere are referred to as Lesser Circles. |
| Ground screws | Ground Screws are used to secure a structure such as a geodesic dome to the ground below. Like a wood screw, it screws into the ground allowing the earth to compress around it. There are many variations of ground screws and applications, such as securing decking, fences and foundations. |
| Hubs (connectors) | A hub is the point at which struts (vertices) come together. It also refers to parts that hold struts together. |
| Icosahedron | Based on the basic pentagon shape. A dome made using icosahedron triangles is the most common dome construction method. |
| OSB | Oriented Strand Board. OSB is made from thin wood strands mixed with wax and adhesives then and then hot pressed into sheets. About 50 layers of strands make up one sheet. Building codes usually use “wood structural panel” as a term to describe the use of plywood and OSB. |
| Piers | Foundation columns that are formed by pouring liquid concrete into holes drilled into the ground. Round forms such as Sonotubes are also often used. |
| Plywood | A structural material made of layers of wood glued together, usually with the grains of adjoining layers at right angles to each other. |
| Polycarbonate panels | Polycarbonate plastic is mouldable, durable, lightweight, flame resistant, shatterproof, and energy efficient. One of its best properties is high-impact resistance, which can be more than 200 times greater than tempered glass. A polycarbonate panel is extremely weather resistant, will not yellow in harsh sun, and recyclable. Ridged sheets of polycarbonate are often installed over walkways, patios and terraces to filter and reduce ultraviolet sunlight, as well as provide rain and snow protection. |
| Polyhedron | A solid figure consisting of four or more plane faces (all polygons), pairs of which meet along an edge, three or more edges meeting at a vertex. In a regular polyhedron all the faces are identical regular polygons making equal angles with each other. Specific polyhedrons are named according to the number of faces, such as tetrahedron, icosahedron, etc. |
| Principal Triangle (PT) | One of the triangles of the polyhedron used in development of the threee-way grid of the geodesic form. It may be planer (PPT) or it may be spherical (PST). |
| PVC | Synthetic thermoplastic material made by polymerizing vinyl chloride. The properties depend on the added plasticizer. The flexible forms are used in hosepipes, insulation, shoes, garments, tarpaulins, etc. Rigid PVC is used for moulded articles. |
| Radius | The distance from the center of your geodesic dome to its edge, or perimeter. |
| Shrink wrap | A sheet or film available in many thicknesses that shrinks in size when heat is applied to it. It can be made to shrink in one direction (unidirectional) or in both directions (bidirectional). Blue marine shrink wrap is the most visible use for large items requiring a protective layer. Thicker and more flame-resistant variations are also available. |
| Snow load | The weight of snow a structure can withstand. Usually expressed in pounds per square feet or KPa (20.9 psf equals 1 kPa). Most structures are safe for 20 to 25 pounds of snow. Snow has about 1/10th the density of liquid water. |
| Struts | For geodesic domes, it’s the pipe or wood beams (ex.: 2″X 4″) used to build your structure. |
| Tarp (tarpaulin) | Large sheet of durable, resistant and water-resistant/waterproof material. It often as comes as a polyethylene sheet or canvas coated with PVC, urethane or polyethylene. Tarpaulins commonly have reinforced grommets along its edges allowing them to be held down or even suspended. |
| Tensegrity | The word ‘tensegrity’ is a contraction of ‘tensional integrity, a pattern that results when push and pull have a win-win relationship with each other. The continuous pull is balanced by the discontinuous push producing an integrity of tension – compression. An example of this is a circus tent supported by cable and rope; the opposite forces apllied by the design of the rope and the strength ,or tensegrity of the rope and cables provide the soundness of the structure. |
| Tensile (stength) | The maximum amount of tensile stress that it can take before failure, for example breaking. Other definitions are “Yield strength”, the stress which will cause a permanent deformation, “Ultimate strength”, the maximum stress material can withstand. and “Breaking strength”, the stress coordinate on the stress-strain curve at the point of rupture. |
| Tesselation | A tessellation is created when a shape is repeated over and over again covering a plane without any gaps or overlaps. |
| Tetrahedron | A type (subdivision) of a polyhedron whith four faces. It is smallest type of polyhedron. |
| Trapezium | Another term to describe a trapezoid. It has for sides (quadrilateral). It can have only one pair of opposite parallel sides or none. |
| Triacon | The subdivision of a polyhedron, often used in the early days of geodesics, the one Buckminster Fuller, the father of geodesics primarily used. You will find references to this subdivision class in books such as Domebook 1 and 2. Triacons are also known as Class II or octahedron. |
| Truncation | To cut off part of a dome along a line. Usually expressed as a fraction of the full sphere. For example a dome which is 3/8th of a full sphere is simply referred to as a 3/8 dome. |
| Tyvek | Tyvek® from Dupont, also commonly known as house wrap or Spunbonded Olefin (high-density polyethylene), is another possibility for covering your geodesic dome. Among many features t is very difficult to rip. it can be sewn and it’s weatherproof. You come across Tyvek® every day, from FedEx and CD envelopes, even protective clothing. It’s lightweight, flexible, smooth, resistant to water, rot and mildew, chemicals, abrasion, and aging. It has a high strength-to-weight ratio and is pH neutral. Tyvek® is offered in 2 basic types: Type 10, a “hard,” area-bonded product, is a smooth, stiff non-directional paper-like substrate withgood printability in both sheet and roll form; Types 14 and 16 are “soft,” point-bonded products with an embossed pattern, providing a fabric-like flexible substrate with good printability and tear resistance. |
| Vertex | Any and every geodesic dome has vertices (plural of vertex). It is the point at which struts connect to each other. |
| Wind load | The total force exerted by the wind on a structure or part of a structure. Usually expressed in pounds per square feet or KPa (20.9 psf Equals 1 kPa). |
| Zapoche | Mentionned in Domebook2 as an inclined prolate spheroid, but can also be an inclined oblate spheroid (golden-ratio “squashing.”) |
