University of Twente Student Theses


Generating temporal 3D city models of Shahjahanabad for exploratory ground-level visibility analysis

Rajan, MSc Vaibhav (2022) Generating temporal 3D city models of Shahjahanabad for exploratory ground-level visibility analysis.

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Abstract:Many ancient 3D city models have been produced in the past for different cities for many different applications. Indian cities like Delhi hold a rich heritage of culture, tradition and art reflected in their present urban form inherent from the past. Creating 3D temporal city models not only becomes a platform to experience the past but also serves as a tool to produce quantitative evidence to infer the present deteriorating state of the city. In our research, we create two temporal 3D LOD-2 city models of Jama Masjid and its surrounding area in Shahjahanabad (Old Delhi) to test its applicability on ground-level visibility analysis for the purpose of heritage conservation. We first review the intertwined dilemma of the present conservation state and overall living conditions with the economic development of Shahjahanabad, a problem whose solution can bennefit from having a temporal 3D city model. Centring on Jama Masjid mosque, A 300 m radius area was chosen for modelling. For the present model, Very High Resolution (VHR)WORLDVIEW- 1 stereo pairs from 2021 and PLEIADES tri-stereo pairs from 2020 were used to generate a 49 cm Digital Surface Model (DSM). We used a state-of-the-art deep learning method, "ResDepth", to detect ground surfaces and interpolate the Digital Terrain Model (DTM). The elevation models were further used to produce normalized DSM, which formed the base of the model. Then, shapefiles of building footprints were used to extract height values from the raster nDSM. Lastly, the shapefile was extruded and exported to multipatch and other formats for rendering purposes. WORLDVIEW-3 30 cm VHR image was used to texture the model. For the past model, we used high-resolution (70 cm) HEXAGON KH-9 surveillance stereo images from 1977. Historic satellite images lack intrinsic parameters, which are very important in the generation of DSMs. These parameters were extracted by adapting a novel approach in NASA’s Ames Stereo Pipeline (ASPy). Having obtained the image parameters, the past city model was made from the produced DSM (77.5 cm), following the same approach as the present city modelling. We call the model of the past the 1970s model and the present as 2020s model. The accuracy assessment for the 2020s model was performed on the nDSM through 21 surveyed building heights. For the 1970s, ground elevation values from the present DTM were compared with the past DTM. The RMSE values for the 2020s and 1970s models were 2.15 m and 3.40 m, respectively. Comparing the two models showed significant changes in the heights of the buildings indicating vertical expansion of the city. Further, a ground-level visibility analysis was performed using the line-of-sight method to assess the loss in the visibility of the mosque centring the study area. The analysis showed the degradation of the skyline of the mosque prompting a closing discussion on the significance of the results and the methods applied.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:02 science and culture in general, 38 earth sciences, 54 computer science, 74 (human) geography, cartography, town and country planning, demography
Programme:Spatial Engineering MSc (60962)
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