1. Anurag Ohri, Manish Sahu Department of Civil Engineering,
3d Modeling of the Vishwanath Temple, Varanasi Using Close Range Digital Photogrammetry
Anurag Ohri, Manish Sahu Department of Civil Engineering,
Indian Institute of Technology (Banaras Hindu University) Varanasi, India
16th International Scientific and Technical Conference
From Imagery to Map: Digital Photogrammetric Technologies
November 14-17, 2016, Agra, India
November 14, 2016

2. Introduction
The Vishwanath Temple in Banaras Hindu University is the highly visited religious and tourist place of Varanasi.
Well-known for their structural and surface complexity, temple constitute a great challenge to any attempt towards precise and detailed 3D measurements and modeling.
This paper reports about a project using modern techniques of terrestrial and aerial photogrammetry to derive a photorealistic 3D model of Temple.
The accuracy of model is improved by using control points collected using DGPS and Total Station.
Accuracy of model is tested by using various GCP in the site.

3. Problems with Photogrammetric Survey in India
In India Labor cost is very less. Monthly salary of Field Surveyor or CAD operator is $200-$700 per month.
Average Size of Fields to be surveyed: 1 ha to 500 Ha
Work done by small companies having very small capital.
Photogrammetry is not very popular, only used in large projects
Not trained manpower to operate UAV or do the processing of Aerial data.
Myths that it is not possible to achieve high accuracy using Photogrammetry.

4. The Aim of Study
To demonstrate the application of UAV photogrammetry in heritage mapping.
To demonstrate the use of low cost UAV as a mapping tool for small areas.
To do the accuracy assessment of map prepared by using low cost UAVs and software.
To estimate the need of GCPs for achieving desirable accuracy.

6. About Shri Vishwanath Temple
IIT(BHU)
About Shri Vishwanath Temple
Shri Vishwanath Temple is one of the most famous temples and biggest tourist attractions in the holy city of Varanasi.
The temple is situated in Banaras Hindu University and is dedicated to the Lord Shiva.
Shri Vishwanath Mandir has one of the tallest temple tower in India. Total height of the temple is Around 75 meters.
Shri Vishwanath Mandir's construction took thirty-five years to complete ( ).
Total Area= Hectare

7. UAV for Low Altitude Photogrammetric Mapping
Small Unmanned Aerial Vehicles are very cheap.
To perform very low altitude aerial photography
Good for covering small areas.
To get full image of buildings form different direction by flying at different heights and taking photographs at different angles
To supply a cheap and easy system for engineering organization for high frequency needs of aerial photogrammetric survey

8. PLATFORM Vertical: 20 Camera Sensor: 1/2.3" Resolution: 12 MP FOV: 94°
DJI Phantom 4 Quadcopter
Location: GPS/GLONASS
Location accuracy: Horizontal: 10 m
Vertical: 20
Camera
Sensor: 1/2.3" Resolution: 12 MP
FOV: 94°
Cost: US$1,500 only

9. Hardware & Software for Processing
System: Desktop Computer
Processor= Intel i7-4770, 3.4 GHz, 4 Cores
RAM=12GB
Hard Disk: 512 GB
Graphics Card: 1 GB
Operating System: Windows 7 , 64 bit
Cost: US$ 1,500
Software for processing: Photomod UAS, Pix4D Mapper, Agisoft etc.
Cost: US$ 375 per month to US$ 10,000 permanent License

10. Input Data
Adding Images in the project with interior and exterior orientation parameter
Camera calibration Parameters
Block layout Creation
Automatic Aerial Triangulation
Automatic tie points
Accepted Accuracy
Measurement of GCP
Block Adjustment
Point Cloud Densification
Geneartion of 3D textured Messh
Generation of Digital Surface model
Generation of Orthomosaic No No
Yes
Yes
Workflow

11. Flight Planning
Flying Height= 100 m above ground Level (Aerial Photograph)
Both Aerial and Terrestrial Photographs
Aerial Mission: Double Grid
Aircraft Speed= 10 m/s
Camera Angle=30° Oblique to Nadir
Longitudinal Overlap=80%
Side lap=50%
Number of images= 335
Ground Resolution= 8 cm

12. Flight Plan

13. Image Properties

14. Ground control Point
Instrument Used: Sokkia GRX2 GNSS Receivers and Topcon 5" accuracy Total Station.
Number of GCPs: 6
Check Points: 13
Accuracy of GCPS: Horizontal: 2 cm, Vertical: 3 cm

15. Collection of GCP

16. GCP/MTP Manager

17. Location of 3D GCP and Check points

18. Camera Position

19. GCP and Automatic Tie Point

20. Average Ground Sampling Distance (GSD)
7.9 cm
Camera Optimization
0.06% relative difference between initial and optimized internal camera parameters
GCPs mean RMS error
0.026 m<GSD
keypoints per image
median of 12329

21. Computed Image and GCP Points Positions
initial (blue dots) and computed (green dots)

22. Bundle Block Adjustment Details
Number of 2D Keypoint Observations for Bundle Block Adjustment
1.8 million
Number of 3D Points for Bundle Block Adjustment
0.66 million
Mean Reprojection Error [pixels]
0.133
Internal Camera Parameters
Focal
Length
Principal
Point x
Point y
Initial Values
3.722 mm
3.159 mm
2.369 mm
Optimized Values
3.724 mm
3.121 mm
2.274 mm
Uncertainties (Sigma)
0.001 mm
0.002 mm

23. Ground Control Points

24. Check Points

25. Densify Point Cloud 3D Densify Poits:14 million
Average Density (per cubic m)=19

26. Top view of Vishwanath Temple

27. 3D Textured Mesh

28. 3D Textured Mesh

29. Orthophoto

30. Digital Surface Model

31. Adding Grid Values to Point

32. Digital Elevation Model (IDW)

33. Time taken in different step
Team Members: 2
Flight Planning: 30 minutes
Flight to capture images: 1 Hour
GCP Survey: 2 Hours
Project initial Processing with GCPs: 2 hours 30 min
Point Cloud Densification: 1 hour 10 min
3D Textured Mesh Generation: 40 min
DSM and Orthomosiac Generation: 30 min
Digitization of Point and DEM generation: 30 min
Total: Approximate 4 man days

34. Problems with UAV based photogrammetry
UAV technology not fully mature
Need increase flight time, Obstacle avoidance, more regular paths, less crashes etc.
Low quality of GPS/IMU sensors
Safety Concern from UAV
Privacy Concern
Permission from Local Government due to flying restrictions
Camera Problems
Processing software not fully matured, need more research.
Need of high speed cloud base processing.
Software are very expensive, not affordable for small companies
Training of manpower

35. Conclusion
UAV is very cost effective and flexible device for capturing images from low altitude.
More mature sensors in near future (GNSS, IMU, Cameras etc.)
Many diverse applications.
Much scope for data Processing methods.
Accuracy is a concern, but suitable for many applications.
In academics courses, need to include Photogrammetry.
Legal and Security issues are main concern.