c. S. MCCAMY, CHAIRMAN ASP STANDARDS COMMITTEE Solicitation of Comments on a Draft ASP Standard Interested parties are requested to comment, by August 15, 1976, on the Fifth Draft of "American Society of Photogrammetry Usage of the International System of Units." EMBERS of the American Society of garded as a starting point for standardization, M Photogrammetry and other interested rather than the full extent of standardization parties are requested to comment on the fol­ to be expected in ASP. lowing draft standard. Comments should be Present and past members of the ASP submitted to C. S. McCamy, Vice President Standards Committee who contributed to for Science and Technology, Macbeth Divi­ the development of this draft are- sion, Kollmorgen Corporation, P.O. Drawer 950, Newburgh, New York 12550. Com­ David Landen William Pryor ments must be received by August 15, 1976, C. S. McCamy (Chm.) Robert Reeves Gomer McNeil Carl O. Thomas and will be considered by the Committee in Clarice lorton John T. Smith, Jr. arriving at a final draft. The final draft pre­ pared by the Committee will be submitted to the ASP Board of Direction for approval be­ The Committee was assisted by Louis E. Barbrow of the National Bureau of Stan­ fore publication as an ASP standard. The dards, and Louis F. Sokol and Ernest John Committee expects the final standard to be Rubin of the U. S. Metric Association, Inc., palticularly useful to the standards commit­ and received valuable comments on the tees of the divisions of ASP in their prep­ fourth draft from Mr. Charles A. Whitten, ar'!tion of draft standards for a number of Chairman of the Metric System Committee aspects of photogrammetric engineering and of the American Congress on Surveying and remote sensing. Thus, this draft must be re- Mapping. Fifth Draft American Society of Photogrammetry Usage of the International System of Units FOREWORD This standard was prepared by the Stand­ It is the policy of the American Society of ards Committee of the American Society of Photogrammetry to promote simplification Photogrammetry to promote use of the In­ and uniformity in usage of units of meas­ ternational System of Units, to make the pol­ urement by cooperating with other organi­ icy of the Society known, and to make the zations in establishing common use of the rules of use of the SI units readily available International System of Units (Systeme In­ to the members of the Society. ternational d'Unites) with the abbreviation According to the policy of cooperating SI and popularly known as the "metric sys­ with other organizations in establishing tem", and to use this system in all of its pub­ common use of SI units, this document is lications. largely based on and technically consistent PHOTOGRAMMETRIC ENGINEERING AND REMOTE SENSING, 761 Vol. 42, No.6, June 1976, pp. 761-776. 762 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1976 with Standard 1000 of the International Or­ tional foot, but the foot based on the older ganization for Standardization, except that definition was retained as the U.S. Survey the spelling "deka" has been used in place Foot, equal to 1200/3937 metre (or 0.304 800 of "deca" to conform to American usage. 6096 metre), for surveying. The existence of these two slightly different definitions made INTRODUCTION it particularly important that the American n the 18th century weights and meas­ Society of Photogrammetry standardize its I ures differed from one city to the next. usage ofunits, basing all conversions ofunits The Articles ofConfederation (1781) and the of measurements directly related to survey­ Constitution ofthe United States ofAmerica ing on the survey foot. (1790) empowered Congress to establish un­ The use of the term "weight" to mean ifonn weights and measures. At the request either force or mass is very confusing. In sci­ ofthe National Assembly of France, in 1790, ence, the "weight" ofa body means the force the French Academy of Sciences formulated caused by gravity. This force varies in time a system of weights and measures known as and space, observed values differing by over the "metric system." The original "metre" 0.5 per cent at various points on the earth. In was one ten-millionth of the distance from common usage, "weight" usually means the north pole to the equator. The "litre" mass. Because ofthis dual usage, it is wise to was a cube one-tenth metre on a side, and avoid using the term "weight" unless its the "gramme" was the mass of water at 4°C meaning is completely clear. It is important in a cube one-hundredth ofa metre on a side. to know whether mass or force is intended, Multiples and submultiples were all related so the SI system clearly distinguishes two by factors often. France adopted this system units, kilogram for mass and newton for in 1799 and made it compulsory in 1840. It force. was readily adopted by scientists 1. SCOPE everywhere. This standard gives rules for the use of In 1866 the metric system was made law­ units of the International System of Units, ful for use in the United States of America. for their symbols, and for fonning and select­ The International Metric Convention, an in­ ing decimal multiples and submultiples of ternational treaty (1875) ratified by the U­ these units for application in photogram­ nited States and 16 other nations, provided for metry and related fields. A list ofconversion physical standards of length and mass to be factors is given in the Appendix. supplied to the signatory nations. Since 1893, metric standards have been the fun­ 2. GENERAL damental weights and measures of the U­ 2.1 SI is based on seven base units, listed nited States and the customary units, such as in Table 1, and two supplementary units, pounds and yards, have been defined in listed in Table 2. These units, designated tenns of these. "SI units," form a coherent system. In a The Conference Generale des Poids et coherent system of units the product or quo­ Mesures (General Conference of Weights tient of any two unit quantities is a unit of and Measures), abbreviated CGPM, is a dip­ the resulting quantity. lomatic organization of adherents to the Convention, which meets every few years. It TABLE 1. BASE UNITS. controls the International Bureau ofWeights and Measures at Sevres, near Paris, which Quantity Unit Symbol maintains physical standards. The U. S. Na­ tional Bureau ofStandards, founded in 1901, length metre m represents the United States at the CGPM mass kilogram kg and maintains our national physical stan­ time second s dards. In 1960, CGPM extensively revised electric current ampere A and simplified the system and adopted the thermodynamic temperature kelvin K name Le Systeme International d'Unites (In­ luminous intensity candela cd amount of substance mole mol ternational System of Units), with the inter­ national abbreviation SI, for his modernized system. Further improvements and addi­ TABLE 2. SUPPLEMENTARY UNITS. tions were made in 1964, 1968, 1971, and 1975. Quantity Unit Symbol According to the Federal Register dated July 1, 1959, the U. S. foot was redefined as plane angle radian rad solid angle steradian sr exactly 0.3048 metre, known as the interna- SOLICITATION OF COMMENTS ON A DRAFT ASP STANDARD 763 2.2 The following definitions of the units other particles, or specified groups of such are the authorized English translations ofthe particles. international agreements in French: (14th CGPM (1971), Resolution 3) candela-The candela is the luminous intensi­ metre-The metre is the length equal to 1 650 ty, in the perpendicular direction, ofa surface 763.73 wavelengths in vacuum of the radia­ of 1/600 000 square metre of a black body at tion corresponding to the transition between the temperature offreezing platinum under a the levels of 2p,o and 5ds of the krypton-86 pressure of 101 325 newtons per square atom. metre. (11th CGPM (1960), Resolution 6) (13th CGPM (1967), Resolution 5) kilogram-The kilogram is the unit ofmass; it is radian-The radian is the plane angle between equal to the mass of the international pro­ two radii of a circle which cut off on the cir­ totype of the kilogram. cumference an arc equal in length to the :lst CGPM (1889) and 3rd CGPM (1901) radius. second-The second is the duration of9 192631 (ISO Recommendation R31, part I, second edi­ 770 periods ofthe radiation corresponding to tion, December 1965) the transition between the two hyperfine steradian-The steradian is the solid angle levels ofthe ground state ofthe caesium-133 which, having its vertex in the center of a atom. sphere, cuts off an area of the surface of the (13th CGPM (1967), Resolution 1) sphere equal to that ofa square with sides of ampere-The ampere is that constant electric length equal to the radius of the sphere. current which, if maintained in two straight (ISO Recommendation R 31, part 1, second edi­ parallel conductors of infinite length, of neg­ tion, Decemher 1965) ligible circular cross-section, and placed 1 metre apart in vacuum, would produce be­ 2.3 Derived units are usually expressed in tween these conductors a force equal to 2 x terms of base units; for example, velocity is 10-7 newton per metre of length. expressed as metre per second (m/s). Some (9th CGPM (1948), Resolution 2) derived units have been given names and kelvin-The kelvin, unit of thermodynamic symbols; those approved by CGPM are temperature, is the fraction 1/273.16 of the listed in Table 3. thermodynamic temperature of the triple 2.4 The names of decimal multiples and point of water. submultiples of SI units are formed by the (13th CGPM (1967), Resolution 4) mole-The mole is the amount ofsubstance ofa use of the prefixes listed in Table 4.