Geometric Evaluation, Automated DEM and Orthoimage Generation from Along-Track Stereo ASTER Images (original) (raw)
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Accuracy Analysis of Dems Derived from Aster Imagery
ASTER acquires along track stereoscopic imagery, with a spatial resolution of 15 meters. Automatic generation of Digital Elevation Models (DEMs) from these images is a well established process, implemented in many commercial software packages. It can provide relief information for areas with poor coverage of topographic mapping. This paper presents a study of the accuracy achieved in DEMs extracted from ASTER, for an area in Portugal, using the PCI OrthoEngine software. Images were orientated with ground control points (GCP) obtained from topographic maps. Experiments were carried out in reducing the number of GCPs. A number of 5 or 6 GCPs was always required to orient the images, in order to keep the accuracy achieved with larger numbers of points. It was possible to conclude that more use could have been done of the approximate orientation provided in the image header. A grid of points derived from the sensor position and attitude, estimated by onboard equipment, is given in the i...
Performance evaluation of global and absolute DEMs generated from ASTER stereo imagery
2011
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital stereo image could be used to generate Digital Elevation Model (DEM), which represents the terrain elevation in discrete three dimensional (3D) forms. In this research, the performance of the absolute and Global DEMs generated from ASTER stereo image is evaluated for the area of Universiti Teknologi Malaysia (UTM). In doing so, 25 Ground Control Points (GCPs) collected by Global Positioning System (GPS) instrument are used to extract an absolute ASTER DEM. Furthermore, the ASTER Global DEM (GDEM) is acquired for the study area. The accuracy of the DEMs is assessed by comparing them with 20 high accuracy points which were collected using GPS technology. Some statistical parameters such as the Mean Error (ME), Standard Deviation (SD) and Root Mean Square Error (RMSE) are determined for this purpose. The achieved results indicated that the estimated vertical accuracy of the ASTER GDEM is less than 5 m at 80% confidence for the study area while the vertical accuracy of less than 15 m is obtained for the ASTER absolute DEM, which is less than the pixel size of ASTER image. Finally, according to the achieved results, 15 m resolution of ASTER image and the selected number of check points, it can be concluded that the accuracy of DEMs is acceptable for the study area, and could be used for various geoinformation applications.
ACCURACY OF DEM GENERATION FROM TERRA-ASTER STEREO DATA
In this work we studied the accuracy of DEMs generated from ASTER stereoscopic images by automated stereo-matching techniques with two different softwares (OrthoBase PRO and OrthoEngine). We compare several DEMs generated for a test area of 23 km x 28 km situated in the province of Granada (south Spain). This is an area was selected because its variable and complex topography with elevations ranging from 300m up to 2800 m.
Accuracy analysis, dem generation and validation using russian tk-350 stereo-images
The Photogrammetric Record, 2004
ABSTRACT TK-350 stereo-scenes of the Zonguldak testfield in the north-west of Turkey have been analysed. The imagery had a base-to-height ratio of 0·52 and covered an area of 200 km × 300 km, with each pixel representing 10 m on the ground. Control points digitised from 1:25 000 scale topographic maps were used in the test. A bundle orientation was executed using the University of Hanover program BLUH and PCI Geomatica OrthoEngine AE software packages. Tests revealed that TK-350 stereo-images can yield 3D geopositioning to an accuracy of about 10 m in planimetry and 17 m in height. A 40 m resolution digital elevation model (DEM) was generated by the PCI system and compared against a reference DEM, which was derived from digitised contour lines provided by 1:25 000 scale topographic maps. This comparison showed that accuracy depends mainly on the surface structure and the slope of the local terrain. Root mean square errors in height were found to be about 27 and 39 m outside and inside forested areas, respectively. The matched DEM demonstrated a systematic shift against the reference DEM visible as an asymmetric shift in the frequency distribution. This is perhaps caused by the presence of vegetation and buildings.RésuméOn a étudié des couples stéréoscopiques TK-350 sur le polygone d'essai ZONGULDAK au Nord-Ouest de la Turquie. Le rapport base-sur-altitude des couples était de 0,52 et la zone couverte atteignait 200 km × 300 km, avec une valeur au sol de chaque pixel de 10 m. On a saisi des points d'appui par numérisation à partir des cartes topographiques à l’échelle de 1:25 000. On a effectué l‘orientation des faisceaux en utilisant un ensemble de logiciels de l'Université de Hanovre tels que BLUH et « PCI Geomatica Ortho Engine AE ». Les essais ont montré que les stéréo-couples TK-350 pouvaient fournir une précision d'environ 10 m en planimétrie et 17 m en altimétrie sur le géopositionnement 3D. On a réalisé un MNA d'une résolution de 40 m avec le système PCI, que l'on a pu comparer avec un MNA de référence obtenu par numérisation des courbes de niveau des cartes topographiques au 1:25 000. La comparaison a montré que la précision dépendait essentiellement de la nature du terrain et de la pente locale. C'est ainsi que les erreurs moyennes quadratiques en altimétrie atteignent 39 m dans les zones boisées, contre 27 m en dehors. De plus, le MNA obtenu a présenté des systématismes par rapport au MNA de référence, sous la forme de décalages asymétriques dans la répartition des fréquences. La cause en est peut-être la présence de bâtiments et de végétation.ZusammenfassungIn diesem Beitrag wird über die Analyse von TK-350 Stereoszenen im Zonguldak Testfeld im Nordwesten der Türkei berichtet. Die Bilddaten hatten ein Basis-Höhenverhltnis von 0·52 und deckten ein Gebiet von 200 × 300 km mit einer Bodenpixelgröße von 10 m ab. Für den Test wurden Passpunkte aus einer Topographischen Karte im Maßstab 1:25 000 digitalisiert. Die Bündelausgleichung wurde mit dem Programmsystem BLUH der Universitt Hannover durchgeführt, weitere Analysen mit dem Paket PCI Geomatica OrthoEngine. Die Tests zeigten, dass mit TK-350 Stereoszenen eine 3D Geopositionierung mit einer Lagegenauigkeit von ca. 10 m und einer Höhengenauigkeit von 17 m möglich ist. Mit dem PCI System wurde ein DHM mit einer Gitterweite von 40 m erzeugt und mit einem Referenz-DHM, das aus digitalisierten Höhenlinien der Topographischen Karte 1:25 000 abgeleitet wurde, verglichen. Es zeigte sich, dass die Genauigkeit im wesentlich von der Gelndestruktur und der lokalen Gelndeneigung abhngt. Der mittlere quadratische Höhenfehler lag bei 27 m außerhalb von Waldgebieten und bei 39 m innerhalb von Waldgebieten. Das durch Bildzuordnung erzeugte DHM zeigte eine systematische Verschiebung gegenüber dem Referenzdatensatz, was an der asymmetrischen Verschiebung in der Hufigkeitsverteilung zu sehen ist. Diese wird vermutlich durch Vegetation und Gebude verursacht.ResumenEn este artículo se analizan imágenes estéreo TK-350 correspondientes a la zona de ensayo Zonguldak, en el noroeste de Turquía. Las imágenes tienen una razón base-altura de 0,52, cubren un área de 200 × 300 km, y tienen una resolución espacial de 10 m. Los puntos de control utilizados en el ensayo se han digitalizado a partir de mapas topográficos a escala 1:25 000 y se utilizaron los programas BLUH de la Universidad de Hannover y Geomatica OrthoEngine AE de PCI para la orientación. Las pruebas muestran que las imágenes estéreo TK-350 pueden alcanzar una exactitud de hasta 10 m en planimetría y de 17 m en altura en la georeferenciación 3D. Se generó un modelo digital de elevaciones (MDE) con una resolución de 40 m mediante el programa de PCI que se comparó con el MDE de referencia calculado a partir de las curvas de nivel digitalizadas de los mapas topográficos a escala 1:25 000. La comparación muestra que la exactitud depende principalmente de la estructura de la superficie y de la…
Modelling the orthoimage accuracy using DEM accuracy and off-nadir angle
Geocarto International, 2018
Orthoimages are differentially rectified images that are corrected for the distortions caused especially by image tilt and topographic relief. The orientation, digital elevation model (DEM) and off-nadir angle plays an important role in orthoimage accuracy. The orientation error mostly occurs due to the quality and distribution of the ground control points. In this study, an attempt has been made to model the remaining errors by keeping the orientation error constant. To model the accuracy, orthoimages are produced with eight DEMs having different accuracies and are assessed using 50 check points. As the theoretical model cannot reflect the real world exactly, an empirical model is used for estimating the orthoimage accuracy. This proposed model was validated by another dataset. It is concluded that statistically there is no significant difference between the calculated model and real planimetric errors. The proposed model can be used in predicting orthoimage accuracy provided that the DEM accuracy and offnadir angles of the points are known.
Int. Journal of Advances in Remote Sensing and GIS, 2016
Abstract: A Digital Elevation Model (DEM) is a representation of a land surface in a 3 dimensional space with elevation as the third dimension along X (horizontal coordinates) and Y (vertical coordinates) dimensions. DEM is a useful data source in hilly areas terrain analysis; DEM plays an important role in various areas like disaster management, hydrology and watershed management, geomorphology, urban development, map creation and resource management etc. Cartosat 1 or IRS P5 (Indian Remote Sensing Satellite) is a state of the art remote sensing satellite developed and launched by ISRO (May 5, 2005). It has been designed for terrain modeling and large scale mapping applications. This high resolution stereo data has great potential to produce high quality DEM. The high resolution Cartosat 1 stereo image data is capable to provide significant impact in topographic mapping and watershed applications. The objective of the present study is to generate high resolution DEM (10 m and 30 m) and ortho rectified image through Cartosat 1 stereo pair, quality evaluation in different elevation strata, generation of terrain parameters. Aglar watershed in Tehri Garhwal and Dehradun district has been used as the test site. The present study reveals that DEM generated (10 m and 30 m) using CARTOSAT 1 stereo pair is of high quality. The derived terrain parameters like slope, aspect, drainage, watershed boundaries etc., are also of good quality. A comparison of the DEM and the parameter derived from it reveals significant improvement in the quality as compared to the freely available DEM in internet. Keywords: ASTER DEM, CARTO DEM, CARTOSAT 1, Digital Elevation Model, Ortho rectified Image, Photogrammetry, Rational Polynomial Coefficient, Stereo Pair, Terrain Parameters.
Performance Estimation of Aster Global DEM Depending upon the Terrain Inclination
Journal of Indian Society of Remote Sensing, 2012
A digital elevation model (DEM) is a source of immense three dimensional data revealing topograph-ic characteristics of any region. The performance of a DEM can be described by accuracy and the morpholog-ic conformity. Both depend upon the quality of data set, the used production technique and the roughness of the terrain. The global DEM of ASTER (Advanced Space-borne Thermal Emission and Reflection Radiometer) was released to public utilization as free of charge on June 2009. It covers virtually overall the globe using 1 arc-second posting interval. Especially easy availability renders ASTER Global DEM (GDEM) one of the most popular and considerable global topographic data for scientific applications. From this point of view, the performance of ASTER GDEM has to be estimated for different kinds of topographies. Accordingly, six test fields from Spain (Barcelona) and Turkey (Istanbul and Zonguldak) have been preferred depending upon the terrain inclination. Thus, the advantages and disadvantages of the DEM product have been proved by means of a group of advanced performance analysis. The analyses indicate that the performance of ASTER GDEM is quite satisfying at urban areas because of flat topography. On the other hand, terrain slope has negative effect on the results. Especially steep, mountainous, forestry topographic formations and the regions which have sudden changes at the altitude have lower accuracy.
Investigations on Two Methods of DEM Extraction
AL-Rafdain Engineering Journal (AREJ), 2009
Digital Elevation Models (DEM) comprise valuable source of data required for many engineering applications. Contour lines, slope-aspect maps are part of their many uses. Moreover, a DEM theme is an essential layer to be included in most GIS analysis operations. Recent scientific achievements aim to automate acquiring DEMs with the most possible speed and accuracy. This paper studies two methods of DEM data extraction from sample aerial stereopairs, the analytical plotter method versus the digital photogrammetric method (DP). The DEM output of the analytical plotter is used as a reference. This is compared to the work performed using the DP method on the sample photos in digital format. Comparison covers various steps of image orientation followed by DEM collection. Numerical outputs of speed and accuracy are presented and discussed. The tests show that errors in automatically extracted DEMs may result from areas representing ground surface of poor texture or contrast conditions, or it may appear due to imperfect photographic processing. Editing time of the product is a major factor especially in urban/ forest areas. Depending on the specified needs of the user, an erroneous DEM output might be accepted as appropriate digital surface model DSM. Statistical tests detect marginal error types in the output. The paper gives conclusions about some problematic sources with recommendations to improve the product.
COMPARATIVE ANALYSIS BETWEEN DEM FROM TOPOGRAPHIC, ASTER GDEM AND SRTM DEM
The difference between the DEM generated from Topographical map, ASTER DEM 1.5 arc second and SRTM DEM 3 arc second has been determine. As the ASTER GDEM has been known to be the highest resolution global digital elevation model purported to be 30m spacing (1 or 1.5) arc second, we have compared three different DEM’s by digitizing the contour of the existing topographical map covering the research area and downloading the ASTER GDEM data and SRTM data from online source. 3-D coordinates of some scattered was selected and generated from the three DEM created. Contour was also generated from the all the DEMs for further comparison. However, the contour value on the existing topographical map was converted from feet to meter to correspond with the ASTER GDEM and the SRTM DEM unit. The result of this research work was based on the Models generated from the 3D data obtained from the topographical DEM, ASTER GDEM and the SRTM DEM, Geographic information system GIS software like Global Mapper 13, Surfer 10 and ArcGIS 10.0 software was also used in doing the analysis. The height obtained from the topographic map was orthometric Height while the ASTER GDEM/SRTM DEM is an ellipsoidal height.