GLOSSARY Aerial photography. Aerial photography is the specialists, CAD allows images to be imported and Amateur or handheld GPS devices are not cor- capturing of images of a site or location from an data added manually or input directly from survey rected by a ground-based station and range in aircraft. It provides an efficient and effective means instruments. Data can be displayed in different accuracy between 5 and 15 meters. of quickly documenting the condition of a large site ways, including 2-D orthographic projections or Ground-penetrating radar. Ground-penetrating or a number of sites. It documents many relevant 3-D isometric, or perspective, views. Information radar (GPR) is a nondestructive technique that uses matters and, if sufficiently detailed, can be a can be divided using multiple layers, or views, electromagnetic waves to investigate the under- substitute for conventional mapping and for which can then be recombined in various ways. ground or internal structures of natural and monitoring purposes. There are two general Database. A database is a collection of various human-made objects. It has been used successfully sources for obtaining aerial photography: archival types of data, including photographic images, in investigating the characteristics of and damage research and commissioning flights. Archival sketches and measurements, condition assess- to walls and masonry structures, such as voids, research is a cost-effective means of acquiring ments, and other pieces of information stored in a detachment, cracks, leaks, and deteriorated mortar images of a site taken for other reasons such as systematic way for security and easy retrieval. joints. GPR has a good level of accuracy and is easy road engineering or national topographic mapping Individual records, or data, are separated into sets, to handle and transport. The GPR basic system programs. Aerial images obtained by commission- themes, and fields with unique identifiers that consists of a data acquisition unit and two transmit- ing flights can be vertical (straight down) or allow the data to be linked together and queried in ting and receiving antennae. The transmitting oblique (taken at an angle). Professional companies various ways. The database can connect the antenna sends pulses of high-frequency radio usually take vertical images by using expensive, separate pieces of information together. waves. When a wave hits the boundary of an object extra-large-format film or digital cameras mounted that has different electrical properties, the receiv- in the belly of a small airplane. Geographic Information System. A Geographic ing antenna records these variations, known as Information System (GIS) is a geographic database Automated monitoring system. An automated anomalies, which are reflected in the return signal. that combines spatial information in graphic form monitoring system contains a large number of with tabular data. It is an effective descriptive, Infrared reflectography.Infrared reflectography different sensors and devices that collect various analytical, and communication tool to map and (IRR) is a nondestructive digital or photographic data measurements. These include but are not assess sites and prioritize necessary work. imaging technique that uses a specialized digital limited to inclinometers, to measure the degree of detector or heat-sensitive film to capture absorp- inclination; levelometers, to measure differential Global Positioning System. A Global Positioning tion and emission characteristics of reflected settlement; weather stations, to measure wind System (GPS) is a navigation and mapping tool that infrared radiation between 750 and 2000 nanome- speed and direction and ambient temperature; and employs special equipment to receive radio signals ters. IRR is simple, quick, and effective in investi- strain gauges, to measure crack propagation. These transmitted from a network of twenty-four satel- gating surface conditions by detecting original devices usually are connected to computers to give lites circling the Earth twice a day in precise orbits. faded or hidden drawings, and in penetrating continuous data to engineers. It allows the rapid acquisition of detailed and through upper layers of overpainted surfaces. comprehensive data with pinpoint accuracy. Two Computer-Aided Design and Drafting. Com- categories of GPS radio receivers range in accu- Laser scanning. Laser scanning uses various puter-Aided Design and Drafting (CAD) is software racy. For these two categories, accuracy can be scanning technologies to provide a 3-D record of a into which measurements, data, and images from improved to several centimeters with a differential surface. In general, these technologies are based on multiple tools and methods can be combined. CAD signal, which is a ground-based radio transmitter. one of three methods: (1) time of flight, in which a is flexible enough to allow the user to produce This base station transmits radio signals that laser pulse is emitted and the time of light travel is quick, basic sketches, as well as drawings of great supplement the radio signals from the satellites. measured; (2) phase comparison, in which the precision and detail. Serving as the common instrument emits a known frequency of light and platform for printing and sharing data among GLOSSARY ILLUSTRATED EXAMPLES 145 compares the returning phases; and (3) triangula- points can be measured using a tape measure or method of recording conditions manually over a tion, in which an emitter and receiver are sepa- survey instruments (total station). These measured printed and scaled image base map. Conditions are rated by a known distance and the angle of the distances correct the angle or tilt in the original then digitally scanned and incorporated back into reflected laser is used to determine distance. With image while retaining the correct proportions of the base map. these technologies, XYZ coordinates are recorded the building. Urban study. An urban study is a detailed survey as millions of individual points. Close together, Sketch diagram. A sketch diagram is an investi- of a historic urban environment. It provides these individual points form a point cloud from gative and interpretative drawing tool that com- answers to important questions related to prob- which a “mesh” can be generated to create a 3-D bines various methods of recording to understand a lems, deficiencies, and economy, and identifies model. site, building, or object. The diagram represents the general planning measures and specific actions Manual recording techniques. Manual record- relationships between elements in order to under- required. Reconnaissance of the historic area ing techniques use tools such as plumb bobs, stand how they interact. It also facilitates commu- focuses on six key issues. The first two, buildings measuring tapes, and paper and pencil to record nication about these key elements. and open spaces—the solids and voids that consti- buildings or sites. Although often labor intensive, tute the urban fabric—are the essence of the historic Three-dimensional computer modeling. these techniques are readily available and allow city and embody its character. The remaining 3-D computer modeling is software that processes the study of buildings or sites in great detail. four—people, land use, traffic, and infrastructure— XYZ coordinate points and builds meshes that Usually this method of recording provides suffi- determine the function of the historic core and have can be formed into different shapes to represent cient information and accuracy with which to a direct impact on its long-term survival and architectural elements. Images of the actual begin conservation. well-being. architectural elements can then be draped or Photogrammetry. Photogrammetry is a survey projected over the surface of these meshes. The Video technology. Video technology is an elec- technique in which a 2-D or 3-D object may be resulting images can be displayed and rotated on tronic tool used to capture and process a large measured from photographs taken from slightly the computer to be viewed from different places. number of images and sound in sequence. It is different positions. These stereographs provide two therefore the ideal tool to record motion and Total station theodolite. A total station theodo- different views of the same object that mimic the processes. Video is also referred to as the technol- lite is a standard survey device consisting of a perspective of human binocular vision. Measure- ogy used to edit and transmit images and sound. powerful telescope mounted on a base that rotates ments are extracted from the stereographs, and 3-D both horizontally and vertically. An operator can information is reconstructed using computer locate points by measuring distances through an software and hardware. electronic distance measurement (EDM) device Rectified photography.Rectified photography is as well as horizontal and vertical angles. Trigono- based on the concept of bringing the surface of an metric calculations are performed by an onboard object, say a building facade, and the plane of the computer, combining the horizontal and vertical image (photograph) into parallel. Rectification angles with the EDM to determine an XYZ coordi- removes perspective, angle, and camera lens nate. A series of points can be combined to form distortion, and creates a measurable image that is lines and planes, thus representing the object on the same plane as the building. It is inexpensive being recorded.