PhotogrammetryThe first aticle in my review has the following title : Microcomputers and Photogrammetry. A new Tool: The Videoplotter. It was written by Angrad, Ganon, and Nolette. This article describes the prototype of a new type of a new type of instrument called videoplotter which consists of a microcomputer with a high resolution monitor and driven by appropriate software. It shows how stereo-images are stored in a digital form and displayed on a screen on which 3-D measurements and plotting can be achieved, using a stereoscope, digital mapping techniques, and a measuring mark that has the advantage of being part of the image matrix ( Agnard et al.
, 1165 ). The article gives a full description and use of the videoplotter. Two main parts are recognized: the Hardware part and the Software part. The hardware of the videoplotter consists of: an IBM-PC XT with 2 floppy disk units, a color monitor, and a mirror stereoscope mounted in front of the monitor. The two stereo images are displayed on the screen and a measuring mark is brought into contact with the corresponding image points, which are observed in 3-D by the poerator ( Agnard er al. , 1166 ).
The software part is mainly an appropriate program that performs the necessary processing and computation of relative and absolute orientation from the screen-coordinate measurements. Testing of the system was carried out by means of an expeeriment in which a paper diapositives of a model were produced and digitized with an HP Scan-Jet digitizer. An object was then chosen and a rectangular grid was projected on the object. Well-defined points and other targets were placed at different spots on the object. The BC-1 analytical plotter was used to determine the ground coordinates of there targets.
By comparing the BC-1 ground values with that obtained by the videoplotter, the order of accuracy of the new systemcan be obtained. The final results showed that the accuracy fall within the 1-mm ecpected order of accuracy ( Agnard et al. , 1166 ). The article concludes by mentioning some ways to improve the system.
More sophisticated software, higher resolution and speed digitizers, higher speed and capacity computers, and higher resolution color monitors are needed to improve the system. The second article has the following title: Digital Terrain Models: An Overview. It was written by F. Doyle. In this article, the definition, origin, acquisition, storage, application, and furure of DTM data, are discussed. The author started by giving the following definition ( Doyle, 1481 ):A Digital Terrain Model ( DTM ) is an ordered array of numbers that represents teh spatial distribution of terrain characteristics.
The spatial distribution is represented by an XY horizontal coordinate system and the terrain characteristic which is recorded is the terrain elevation Z. We can use an alternative approach to define position by latitude, longitude, and terrain elevation. The term DTM had its origin in work performed by Prof. C. L. Miller at MIT about 1955-60.
A DTM system has four major elements:* Digital Data Acquisition:DTM data can be acquired from existing maps by manuallyor automatically following contour lines using digitiziing tables or by using scanning devices. The second major source of digital data is from photogrammetric steremodels where encoding devices which are bulit in most photogrammetric systems record teh data on paper or magnetic tape. Some photogrammetric instruments are equipped with automatic image correlators, and produce a high density elevation points. Ground surveys are another source of DTM data. Direct source of digital elevation data are radar and laser altimeters carried in aircraft and spacecraft and spacecraft ( Doyle, 1482 ).
*Digital Data Preprocessing: Acquired DTM data needs extensive computer preprocessing to arrange the data in the appropriate format. Preproceesing includes data editing,format conversion, coordinate transformation, and interpolation ( Doyle, 1483 ). * Data Storage and Management: DTM data must be organized so that they can be identified,stored, and retrieved in an efficient manner. The basic storage medium is magnetic tape. In order to mange the date files, they must be croossindexed by content and coverage ( Doyle, 1483 ). * Applications of DTM data:One operation that is involved in the application is, given XY, and asked to find Z.
In addition, given an array of XYZ coordinates sets at fixed intervals, plotting to find the value of Z at any other value of XYZ. Some the direct application of DTM are asfollows ( Doyle, 1484 ): 1. Determination of contour lines. 2.
generation of profiles. 3. Generation of perspective views. 4. Earthwork calculations. 5.
Navigation control system. 6. Terrain simulation. 7. Terrain models. In conclusion, the rapid development in the ability to handle terrain data in completely digital form holds forth the promise of reducing the drudgery of cartographic operations, and of reducing time and cost so that managers and decision makers will know how to make the maximum utility of the resources of the world ( Doyle, 1485 ).
REFRENCES*Agrad, J. P. P. A. Gogan, and C.
Nolette, (1988). Vol. 54, No. 8, p: 1165-1167.
Microcomputers and Pjotogrammetry. A new tool: the Videoplotter. Photogrammetric Engineering and remote Sensing,*Doyle, F. J. , (1978).
Vol. 44. No. 12, p: 1481-1485.
Digital Terrain Models: An Overview. Photogrammetric Engineering and Remote Sensing,*Fussell, J. And D. Rundquist, (1986). Vol.
52, No. 9, P: 1507-1511, On Dfining Remote Sensing. Photogrammetric Engineering and Remote Sensing,*Keating, T. J.
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E. , (1979). Vol. 45, No. 2, Digital Map Revision. Photogrammetric Engineering and Remote Sensing,P: 193-200.
Lin, Hsin-Piao, 1998, Vol. 34, P: 1524-1525, Photograametric prodiction of mobile satellite fading in roadside tree-shadowed environment, Electronics LettersKalkhan, M. A. (1998). Vol.
19, P: 20499-2060, Assessing the accuraxy of Landsat Thematic Mapper classification using double sampling. International Journal of remote Sensing. Fraser, C. S. , (1998).
P: 37, Some Thoughts on the Emergence of Digital Close Range Photogrammetry. PgreayObaidat, Mohammed Taleb. , (1998). P: 3-25, Video system to monitor archeological sites using ground-based photogrammetry. Journal of Surveying Engineering.
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