Wani Sofia Udin

Digital aerial imagery of unmanned aerial vehicle for various applications

Digital aerial imagery (DAI) can be acquired using digital mapping camera attached to light aircraft. The DAI is used for the production of topographic and thematic map. The cost of acquiring DAI is very expensive and suitable for large area coverage. The acquisition of DAI is not economical and suitable for small area coverage. Therefore an alternative method should be used to fulfill this need. There are two alternative methods that can be used for acquisition of DAI which include using a small format digital camera attached to light aircraft and using a small format attached to an unmanned aerial vehicle (UAV). UAV system has been reported used in various and diversified applications such as mapping applications (eg. map revision, landslide, coastal erosion, archaeology, forestry), industrial application (eg. engineering, crash accident), Geographic Information System (GIS) applications and others. In this study, micro unmanned aerial vehicle (UAV) systems which comprise of fixed wing UAV flying and rotary UAV are attached with small format high resolution digital camera to acquire DAI for the purpose of mapping at the flying height of 300m at 100m respectively. The micro UAVs were flown autonomously (i.e automatically) and a series of DAIs of a slope using fixed wing UAV and a stream using rotary UAV were acquired rapidly within short period. Ground control point (GCP) and check point (CP) were established using the Global Positioning System and conventional Total Station techniques around the study area for the slope and stream respectively for the purpose of digital image processing and accuracy assessment. The DAIs were processed to produce photogrammetric output such as digital elevation model (DEM) and orthophoto. All these photogrammetric products were successfully produced and assessed. The achievable accuracy is less than ±1m for slope mapping and ±0.280m for stream mapping. In this study, it is proven that the micro UAV system can be used for mapping which cover small area. As conclusion, micro UAV is suitable for mapping small area, rapid data acquisition, accurate, low cost and can be employed for various applications.

Assessment of Photogrammetric Mapping Accuracy Based on Variation Flying Altitude Using Unmanned Aerial Vehicle

Photogrammetry is the earliest technique used to collect data for topographic mapping. The recent development in aerial photogrammetry is the used of large format digital aerial camera for producing topographic map. The aerial photograph can be in the form of metric or non-metric imagery. The cost of mapping using aerial photogrammetry is very expensive. In certain application, there is a need to map small area with limited budget. Due to the development of technology, small format aerial photogrammetry technology has been introduced and offers many advantages. Currently, digital map can be extracted from digital aerial imagery of small format camera mounted on light weight platform such as unmanned aerial vehicle (UAV). This study utilizes UAV system for large scale stream mapping. The first objective of this study is to investigate the use of light weight rotary-wing UAV for stream mapping based on different flying height. Aerial photograph were acquired at 60% forward lap and 30% sidelap specifications. Ground control points and check points were established using Total Station technique. The digital camera attached to the UAV was calibrated and the recovered camera calibration parameters were then used in the digital images processing. The second objective is to determine the accuracy of the photogrammetric output. In this study, the photogrammetric output such as stereomodel in three dimensional (3D), contour lines, digital elevation model (DEM) and orthophoto were produced from a small stream of 200m long and 10m width. The research output is evaluated for planimetry and vertical accuracy using root mean square error (RMSE). Based on the finding, sub-meter accuracy is achieved and the RMSE value decreases as the flying height increases. The difference is relatively small. Finally, this study shows that UAV is very useful platform for obtaining aerial photograph and subsequently used for photogrammetric mapping and other applications.

Digital Terrain Model extraction using digital aerial imagery of Unmanned Aerial Vehicle

Digital Terrain Model (DTM) is extensively applied in various fields such as surveying and construction engineering, natural disaster management system, structure monitoring, and many more. Generally, the demand on accuracy and very detail information of DTM extraction is crucial for most of the applications. The advancement of photogrammetry and spin-off technology has advantageous in extracting highly accurate DTM. Currently, the DTM can be extracted from digital aerial imagery of small format camera mounted on light weight platform such as Unmanned Aerial Vehicle (UAV). The study is performs to assess the accuracy of DTM derived from UAV platform. Canon PENTAX W90 is utilized as non-metric camera for the earth information acquisition. In this study, 23 points of three dimensional coordinates (3D) were established using real time kinematic Global Positioning System (RTK-GPS) technique. Sixteen points are used in ground control point (GCP) for the purposes of aerial triangulation while seven as check point (CP) for accuracy assessment. The research output is then evaluated for planimetry and vertical accuracy using root mean square error (RMSE). Based on the analysis, sub-meter accuracy is obtained. As conclusion, UAV digital imagery can be used for accurate applications.

Calibration of high resolution digital camera using self-calibration bundle adjustment method

Currently, the price of digital camera is decreasing and many users afford to purchase it. The digital camera can be used for many applications. The digital camera can also be used for accurate measurement such as determination of three dimensional (3D) coordinates, production of accurate measurement and generation of 3D model of objects. However, the digital camera need to be calibrated to obtain accurate results. The aim of this study is to calibrate the digital camera so that it could be used for accurate measurement. In this study, close range photogrammetric technique was used to calibrate three high resolution digital cameras. The digital cameras used comprise of Rollei D30, Nikon D60 SLR and compact Nikon Coolpix S560. The three digital cameras were used to acquire photographs of three different sizes of testfield that are equipped with retro-reflective targets. The approximate 3D coordinates of the different testfield were estimated by measuring it manually. The three digital cameras were calibrated using self-calibration bundle adjustment method. The photographs of the testfield were acquired using potrait and landscape setup for each camera location in 3D space. After the acquisition of the photographs of the testfield, they were downloaded into the computer for the measurement process of the retro-reflective targets and subsequently the final 3D coordinates of the retro-reflective targets were determined using the self-calibration bundle adjustment method. The coordinates of the retro-reflective targets were also determined using intersection method of total station which were used as referenced value. The 3D coordinates from the digital camera were then compared with the 3D coordinates of the total station. Results showed that the Nikon D60 SLR digital camera is superior than the other two digital cameras in term of accuracy and network precision. The next best result is shown by the Nikon Coolpix S560 compact digital camera and finally the Rollei D30. For the Rollei D30, the results are less accurate than the Nikon D60 SLR. However, the interior orientation parameters of this camera are very stable. In conclusion, all the three high resolution digital cameras have the potential to be used for various close range applications.

Accuracy assessment of aerial triangulation using different format of aerial photograph and digital photogrammetric software

The advancement in digital photogrammetry has made photogrammetric technique become simpler, faster and lower cost. This method is popular in covering large and small area. This paper discusses about the experience of processing a strip of large format aerial photographs and two strips of small format aerial photographs using different digital photogrammetric software. The study area covered is the area of Universiti Teknologi Malaysia main campus and its surrounding area. Secondary data of ground control points and check points established using rapid static technique of GPS were used. In this study, two digital photogrammetric softwares were used for image processing and produce several photogrammetric output such as aerial triangulation, DTM and digital orthophoto. Two types of analysis were carried out that are point and visual analysis. The results showed that the large format aerial photograph produces more accurate compared to small format aerial photograph. Also it was found that the results of one of the digital photogrammetric software is superior that the other software. This study proved that digital photogrammetry can be utilised to process large and small format aerial photograph at sub-meter accuracy.