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Digital ortofotolarda sayısal arazi modellerinin doğruluğu

Accuracy of digital terrain model in digital orthoptoros

  1. Tez No: 75435
  2. Yazar: HANDE DEMİREL
  3. Danışmanlar: PROF. DR. M. ORHAN ALTAN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Jeodezi ve Fotogrametri, Geodesy and Photogrammetry
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1998
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Fotogrametri Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 100

Özet

ÖZET: Digital ortofotolar, sayısal ortamdaki bilgilere duyulan ihtiyaç, doğruluk ve güvenilirlikleri nedeniyle haritacılık alanında hızla kullanılmaya başlamışlardır. Uzmanlaşılmış arazi bilgisine ihtiyaç duyulan coğrafi bilgi sistemlerinde tabaka veya veri tabam olarak, mühendislik yapılarının planlanmasında, örneğin yol yapım projelerinde, güncelleştirme ortofotolar kullanılabilir. Ortofoto; eğikliği, topografik yerdeğiştirmesi ve bazı durumlarda kamera distrosyonu düzeltilmiş bir fotografîk üründür. Digital ortofotolar ise diferansiyel düşeye çevirme işleminin bilgisayar ortamında gerçekleştirilmesi sonucu elde edilmektedirler. Bilgisayar teknolojisindeki hızlı gelişmeler pek çok alanda olduğu gibi haritacılık sektöründe de yeni bir dönem başlatmış, analogortofoto örneğinde olduğu gibi pek çok işlem daha hızh, ucuz ve doğru olarak gerçekleştirilebilmektedir. Digital ortofoto elde etmek için gerekli veriler digital görüntü, kamera kalibrasyon verileri, dış yöneltme elemanları, kontrol noktası koordinatları ve sayısal arazi modelidir. Bu bileşenler içersinde digital ortofotonun doğruluğuna etki eden en önemli faktör sayısal arazi modelidir. Sayısal arazi modelleri uygun bir yazılım kullanarak arazinin dayanak noktaları yardımıyla matematiksel olarak ifade edilmesidir. Ortofotolarda arazi sayısal arazi modeli referans alınıp düşeye çevrildiğinden, sayısal arazi modelinin doğruluğu doğrudan ortofotoyu etkilemektedir. Sayısal arazi modellerinin doğruluğu; yüzeydeki seçilmiş ve dağılmış noktaların ölçülmesine, ölçme yöntemlerine, örnekleme noktalarının dağılımı ve yoğunluğuna, arazideki karakteristik özelliklerin değerlendirilmesine ve arazi yapısına bağlıdır. Bu çalışmada hedeflenen, ulaştığı doğruluk, birleştirilmiş sayısal görüntü ve üç boyutlu verileri ile günümüz haritacılık uygulamalarında geniş kullanım alam bulan digital ortofotolann tanımının yapılması, üretim aşamalarının incelenmesi, karşılaşılabilecek problemlerin belirtilmesi ve üretim sırasında sayısal arazi modeli dayanak noktalarının fotogrametrik yöntem ile elde edildiğinde ulaşılacak doğruluğun analizidir. vu

Özet (Çeviri)

SUMMARY ACCURACY OF DIGITAL TERRAIN MODEL IN DIGITAL ORTHOPHOTOS There is an enormous development in computer technology at recent years. Because of increasing demands for digital information and automation, producing maps by digital techniques becomes popular. There is a huge demand for better and more reliable map information. As standard-mapping techniques can not fulfil this demand, this gap can be fulfilled by digital orthophotos. An orthophoto is a photogrammetric image that is differentially rectified to remove any distortion due to photographing geometry and relief displacement. In other words, digital orthophotos represent a geocoded image. Orthophotos are geometrically equivalent to standard line and symbol maps, but instead of lines and symbols, they show actual photogrammetric images. A terrain model is needed to correct the image distortions caused by relief displacement. Developments in scanner technology and digital metric cameras give acceleration to orthophoto map production. The advantages of digital orthophotos are image quality, visualisation, and integration with GIS and achieving computer-supported data. Handling of very high resolution images can cause problems such as; saving the huge amount of raw data very quickly, writing the data on a erasable medium, quickly accessing original images, displaying and interactive measurements, the rectification algorithms supported by data management. The procedure of the orthophoto process can be divided into three steps;. Calculation of geometric parameters. Calculation of anchor point vectors. Orthoprojection The input data for orthophoto process is;. Digital terrain model containing three dimensional ground coordinates vui. Fiducial marks digitised interactively. Approximate fiducial marks in the digital image. Control points digitised in the photo print. Corresponding control points on the ground. Camera calibration report including parameters of inner orientation, calibrated focal length, principle point location, the value of lens distortions, calibrated fiducial marks in the distorted camera image. Exterior orientation of the aircraft, e.g. flight height The usage of digital orthophotos is dependent upon having it produced to a known accuracy. The accuracy of digital orthophoto is related to below factors; Using written into formats with producing hardware and software Camera and focal length Magnification to out put scale Density ratios of diapositives or scanners resolution quality The quality of scanners while scanning raw data and their geometric accuracy The quality of scanned resembles which can be expressed with micron or dpi Differential rectification methods The dimension of out put pixel Radiometric correction Determining control points and their collection method Variance in terrain or in buildings according to focal length Density and quality of digital elevation model (DEM) data IXThe accuracy that can be obtained from digital orthophotos is mostly correlated with digital terrain model that is used for producing digital orthophotos. Digital terrain models (DTM's) and their derivatives, which constructs the elements of 2D or 3D spatial data bases, are routinely used for wide range planning and engineering applications. Due to recent technological developments, DTM generation by digital photogrammetry is becoming a relevant field of research and applications. DTM's is a geometrical description of the terrain surface by digital techniques, mainly by point and line elements. As a concept digital terrain model (DTM) and digital elevation model (DEM) is considered as equal, because the developed DEM data should contain significant topographic features on the land and break lines. Since this technology is still in a developing phase, relevant improvements can be expected in the future either in terms of image calibration and image matching algorithms, or in terms of DTM enhancement through post-processing techniques. There are several methods for acquisition of reference points;. Obtaining the necessary topographic data by field survey. Obtaining the data by means of digitisers from maps.. Data can be obtained by means of satellites, radar and laser altimeters. Data acquisition can be performed by photogrammetric means. The most important source for DEM is profile scanning on a digital photogrammetric system, which, in process of orthophoto mapping, produces DEM data as its by products Grid, in raster formats, triangulated networks and triangulated irregular networks are the three most common basic structures used today for electronically storing, manipulating, analysing and handling of elevation data. These structures can be derived directly from aerial photographs using photogrammetric techniques. The achievement of optimum interpolation method lost interest with the developing of qualified software programs as they give the same performance. The vertical accuracy of a DEM is simply the average vertical error of all points interpolated within the DEM grid. Nowadays, the accuracy of DEM is directly related whether the morphological structures and man-made structures like bridges, motorways, high building are taken into account.The accuracy of DEM is related to below actors;. Points that are distributed and collected on the terrain. Measurement techniques. Frequency and distribution of resampling reference points. In characteristic fields of the terrain reference points should be measured. Structure of the terrain During tiie study both workstation and personal computers was being used nearly for the same purposes, so the opportunity of comparing these systems was put to use. Considering the capacity and speed of workstations, it is obvious that workstations are superior to personal computers. Due to increasing need to automation and speed in digital photogrammetry, map producers, ignoring their high costs are using workstations in a wide range. In order to reduce the costs an on line state wide database, on line control point data base should be provided. The aim of this study is to determine the accuracy and reliability in a digital terrain model, which is obtained by photogrammetric techniques while producing digital orthophotos. Definition and brief history of photogrammetry was given in chapter 2. In addition to these mathematical models of photogrammetry and central projection is studied. In chapter 3 description of orthophotos, mathematical means of rectifying and correction methods was given. The usage of digital orthophotos in different fields was being highlighted. The mathematical base of differential rectification is also included to this chapter. In chapter 4 analogue and digital orthophoto producing steps were studied. The possible problems in producing orthophotos and factors that have an impact on quality of digital orthophotos were examined. It is clear mat quality is more than accuracy. The major factors that effect digital orthophoto quality were highlighted. Concepts of digital terrain model, data acquisition, interpolation methods were studied in chapter 5.The interpolation methods mat were used in the study were examined briefly. In chapter 6, digital orthophotos of 1.T.Ü Ayazaga Campus was being produced and the DTM accuracy in digital orthophotos were examined. For producing digital orthophotos PHODIS OP digital photogrammetric software on a Silicon Graphic XIworkstation was being used. Digital terrain model was being performed on SCOP software. In order to determine the accuracy both photogrammetric data and geodetic data was being used. Two polygon nets were formed and observations were being done by electronic total station for geodetic points. The heights of same spot points were measured in both photogrammetric and geodetic methods. The obtained accuracy is acceptable according to national and international statistical standards. The results were obtained from study of DTM accuracy and interpretations were given in chapter 7. Xll

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