Conservation of Historic Stone Buildings and Monuments (1982) / Chapter Skim
Currently Skimming:
Photogrammetric Measurement and Monitoring of Historic and Prehistoric Structures
Photogrammetric Measurement and Monitoring of Historic and Prehistoric Structures
Pages 242-271
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 242... ...
Controlled stereo photographs can be used as the basis of a number of photogrammetric products, including photogrammetric maps, orthophotos, and combinations thereof. Repetitive aerial and terrestrial photographs of a site, and products derived from them, can be compared to allow the monitoring and documentation of inevitable change in cultural resources.
|
From page 243... ...
BASIC PRINCIPLES OF PHOTOGRAMMETRY Photogrammetry Photogrammetry, in its strictest sense, is measurement using photographs. A single aerial photograph for instance, is a representation of a three-dimensional scene reduced to a two-dimensional format.
|
From page 244... ...
The accuracy of the x, y, and z dimensions derived through parallax measurement and radial line plotting from a stereo pair depends on the quality of the photographs themselves. The film plane must be extremely flat to minimize uncontrolled scale variations within the image, and the lens axis must be accurately perpendicular to and centered over the film plane.
|
From page 245... ...
While metric cameras range in price from $10,000 to $60,000 or more, a number of firms maintain and use them regularly and will enter into contracts for terrestrial and aerial photogrammetry. True horizontal mapping of structures or features from vertical aerial photographs is accomplished through radial line plotting.
|
From page 246... ...
Radial line plotting using a stereo pair of photographs is usually done with a radial plotter or photogrammetric plotter. The instrument uses the center of each vertical photo as a known station and allows the interpreter to position a line from this point through each point of interest on the photograph.
|
From page 247... ...
It is produced by a machine that not only does radial line plotting, but also uses parallax measurement as the basis of changing the scale of very
|
From page 248... ...
A combination of an orthophoto and a photogrammetric line map can be made by first compiling an orthophoto and then using the same controlled stereo pairts) on a photogrammetric plotter to produce a topographic contour map at a desirable scale.
|
From page 249... ...
Topographic contours were compiled using a stereo plotter and photographically superimposed over the orthophoto, thus supplying metric information as well. Such renditions are especially useful as base maps for planning and executing fieldwork.
|
From page 250... ...
-They are used every day by engineers, planners, geologists, cartographers, and many others for the development of topographic and planimetric data. Aerial photographs are taken in scales ranging from about 1:200,000 (small-scale photography)
|
From page 251... ...
The L-shaped white markers in the corners of this scene are ground control panels, set prior to overflight. If these panels had not been set, it would have been necessary to photoidentify points and measure the distances between them later.
|
From page 253... ...
Figure 6 is an aerial photogrammetric map of a prehistoric pueblo structure at Chaco Canyon National Monument with x's marking some of the points digitized during photogrammetric plotting. Digital photogrammetric data can be used in a number of ways in structural documentation.
|
From page 254... ...
SOURCE: Drafted from photogramrnetric data by Jerry Livingstone, Southwest Cultural Resources Center, National Park Service.
|
From page 255... ...
The first product to emerge from a photogrammetric plotter is a manuscript map or drawing. It shows all planimetric detail and three-dimensional coordinates or contours chosen for interpretation, but often is drawn by a pencil or singlewidth plotter pen.
|
From page 256... ...
Drafted maps contain the same information as manuscript maps and are far more useful for publication. Interestingly, during some early experiments in mapping and monitoring structures at the Remote Sensing Division of the Southwest Cultural Resources Center it became apparent that even drafted maps and drawings were not acceptable, or at least not very exciting, to architects.
|
From page 257... ...
but it -- 1 . 1.~ FIGURE 9 Manuscript map of a portion of a histonc, abandoned Hidatsa Village at Knife River Indian Villages National Histonc Site in North Dakota.
|
From page 258... ...
258 ~ 2 ' t~ 3= of, U 11-1~' 1 ,, to 41;~= '5~ oil | ~ ~ ~ o ~ ~ 3 o; ~ ~ ° ~ CL)
|
From page 259... ...
259 ~ ~ cn ~ Cot — ~ o A)
|
From page 261... ...
261 .s 4 o C~ .° ~ o me, Q ~ 4~ em o .
|
From page 264... ...
Because structural monitoring is a historic process, entailing the use of previously collected baseline data and comparison with subsequent data sets, it is vitally important that future means of recording and monitoring be compatible with past photogrammetric data bases. The first step in this process was initiated at Pueblo Alto in Chaco Canyon National Monument, a ruin of the Pueblo-III period occupied during the eleventh and twelfth centuries A.D.
|
From page 265... ...
The ruin of Kin Ya'a, originally built of native sandstone, lies within Chaco Canyon National Monument in New Mexico aIld probably dates to A.D.
|
From page 267... ...
Many monitoring situations may not require the measurement of the potentially large number of three-dimensional point coordinates available in stereo photos, and EDM monitoring of a relatively small number of highly critical points on a structure or site could greatly speed the monitoring process. It would be feasible, for instance, to monitor a small number of points on a structure each day, or con
|
From page 268... ...
A computer could produce almost instantly a comparison map of two digital point matrices recorded from the same site or structure at different times; it is possible that pattern recognition programs could be developed that would register the two data matrices automatically with manual recourse to control points. Ground-based microwave scanners that would allow the scanning of specific structures with sufficient accuracy and resolution have not been developed, and a prototype program probably would cost millions of dollars.
|
From page 269... ...
Reconstruction Digitized three-dimensional photogrammetric data can be used for more than simple representation of a structure or comparison with baseline data for monitoring purposes. In many cases the archeologist or cultural resource manager is concemed with structures that already have suffered considerable destruction or fabric change.
|
From page 270... ...
FIGURE 17 A more detailed, 50 x 50 mesh resolution computer perspective drawing of the sense portion of Pueblo Alto appearing in Figure 16. Note that "hidden lines" are actually hidden in this rendition.
|
From page 271... ...
Research in the application of microwave scanning, holography, and three-dimensional, computer-aided structural reconstruction also may offer the architect new tools for ensuring that the integrity of historic and prehistoric structures is protected. Finally, the methods described in this paper are nondestructive or ninimally hat to architectural materials.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.