Low cost surveying using an unmanned aerial vehicle

Mónica Pérez Saiz, Francisco Agüera Vega, Fernando Carvajal Ramírez


UAV-g 2013. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences – ISPRS Archives 40: 311-315



Traditional manned airborne surveys are usually expensive and the resolution of the acquired images is often limited. The main advantage of Unmanned Aerial Vehicle (UAV) system acting as a photogrammetric sensor platform over more traditional manned airborne system is the high flexibility that allows image acquisition from unconventional viewpoints, the low cost in comparison with classical aerial photogrammetry and the high resolution images obtained. Nowadays there is a necessity for surveying small areas and in these cases, it is not economical the use of normal large format aerial or metric cameras to acquire aerial photos, therefore, the use of UAV platforms can be very suitable. Also the large availability of digital cameras has strongly enhanced the capabilities of UAVs. The use of digital non metric cameras together with the UAV could be used for multiple applications such as aerial surveys, GIS, wildfire mapping, stability of landslides, crop monitoring, etc. The aim of this work was to develop a low cost and accurate methodology in the production of orthophotos and Digital Elevation Models (DEM). The study was conducted in the province of Almeria, south of Spain. The photogrammetric flight had an altitude of 50 m over ground, covering an area of 5.000 m2 approximately. The UAV used in this work was the md4-200, which is an electronic battery powered quadrocopter UAV developed by Microdrones GmbH, Germany. It had on-board a Pextax Optio A40 digital non metric camera with 12 Megapixels. It features a 3x optical zoom lens with a focal range covering angles of view equivalent to those of 37-111 mm lens in 35 mm format. The quadrocopter can be programmed to follow a route defined by several waypoints and actions and it has the ability for vertical take off and landing. Proper flight geometry during image acquisition is essential in order to minimize the number of photographs, avoid areas without a good coverage and make the overlaps homogeneous. The flight planning was done using the MdCockpit software, with the module waypoint editor. Flight route file was downloaded into the quadrocopter autonomous chip via cable. A total of twelve vertical images with a longitudinal and transversal overlapping of 60 % and 50 % respectively were taken. The digital camera was previously geometrically calibrated. Field control points covering the whole studied area were defined over the area of interest and their coordinates were measured by a GPS. Natural targets were used as field control points. The close range photogrammetric software Photomodeler Scanner v.7 was used in this work to calibrate the camera and to carry out the photogrammetric process. The software Golden Surfer was used to produce the DEM. The planimetric and the altimetric root mean square error (RMSE) were calculated in order to check the accuracy of the products. The RMSEx was 6 cm, the RMSEy was 4 cm and the RMSEy was 7 cm. Our preliminary results demonstrate the feasibility and accuracy of orthophotos and DEMs obtained from images captured from a quadrocopter using low cost photogrammetric software. A future work can be the comparison of the products obtained following the route used in this study where the images are taken vertically with the products obtained with an orbital route where the number of images will be diminished and the photos will be taken oblique.

Measuring sunflower nitrogen status from an unmanned aerial vehicle-based system and an on the ground device

Francisco Agüera Vega, Fernando Carvajal Ramírez, Mónica Pérez Saiz 2011 UAV-g 2011. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences – ISPRS Archives 38: 201-206 http://www.scopus.com/inward/record.url?eid=2-s2.0-84924042320&partnerID=MN8TOARS ABSTRACT Precision agriculture recognizes the inherent spatial variability associated with soil characteristics, land morphology and crop growth, and uses this information to prescribe the most appropriate […]

Surveying a landslide in a road embankment using unmanned aerial vehicle Photogrammetry

Fernando Carvajal Ramírez, Francisco Agüera Vega, Mónica Pérez Saiz


UAV-g 2011. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences – ISPRS Archives 38: 201-206



Most of the works of civil engineering, and some others applications, need to be designed using a basic cartography with a suitable scale to the accuracy and extension of the plot. The Unmanned Aerial Vehicle (UAV) Photogrammetry covers the gap between classical manned aerial photogrammetry and hand-made surveying techniques because it works in the close-range domain, combining aerial and terrestrial photogrammetry, but also introduces low-cost alternatives. The aim of this work is developing of an accurate and low-cost method to characterize landslides located on the size of a road. It was applied at the kilometric point 339 belonging to the A92 dual carriageway, in the Abla municipal term, province of Almeria, Spain. A photogrammetric project was carried out from a set of images taken from an md4-200 Microdrones with an on-board calibrated camera 12 Megapixels Pentax Optio A40. The flight was previously planned to cover the whole extension of the embankment with three passes composed of 18 photos each one. All the images were taken with the vertical axe and it was registered 85% and 60% longitudinal and transversal overlaps respectively. The accuracy of the products, with planimetric and altimetric errors of 0.049 and 0.108m repectively, lets to take measurements of the landslide and projecting preventive and palliative actuations.

Digital camera calibration using images taken from an unmanned aerial vehicle

Mónica Pérez Saiz, Francisco Agüera Vega, Fernando Carvajal Ramírez


UAV-g 2011. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences – ISPRS Archives 38: 167-171



For calibrating the camera, an accurate determination of the interior orientation parameters is needed. For more accurate results, the calibration images should be taken under conditions that are similar to the field samples. The aim of this work is the establishment of an efficient and accurate digital camera calibration method to be used in particular working conditions, as it can be found with our UAV (Unmanned Aerial Vehicle) photogrammetric projects. The UAV used in this work was md4-200 modelled by Microdrones. The microdrone is also equipped with a standard digital non-metric camera, the Pentax Optio A40 camera. To find out the interior orientation parameters of the digital camera, two calibration methods were done. A lab calibration based on a flat pattern and a field calibration were fulfilled. To carry out the calibration, Photomodeler Scanner software was used in both cases. The lab calibration process was completely automatic using a calibration grid. The focal length was fixed at widest angle and the network included a total of twelve images with ± 90° roll angles. In order to develop the field calibration, a flight plan was programmed including a total of twelve images. In the same way as in the lab calibration, the focal length was fixed at widest angle. The field test used in the study was a flat surface located on the University of Almería campus and a set of 67 target points were placed. The calibration field area was 25 x 25 m approximately and the altitude flight over ground was 50 m. After the software processing, the camera calibration parameter values were obtained. The paper presents the process, the results and the accuracy of these calibration methods. The field calibration method reduced the final total error obtained in the previous lab calibration. Furthermore the overall RMSs obtained from both methods are similar. Therefore we will apply the field calibration results to all our photogrammetric projects in which the flight high will be close to 50 m.

Geometric accuracy of Ikonos Geo Panchromatic orthoimage products

Manuel A. Aguilar, Fernando J. Aguilar, Fernando Carvajal Ramírez, Francisco Agüera Vega,


Revue Française de Photogrammétrie et de Telédétection. ISPRS Commission Technique I, Symposium, nº 184: 5-10



The new very high space resolution satellite images, such as QuickBird and IKONOS, open new possibilities in cartographic applications. This work has as its main aim the assessment of different sensor models for achieving the best geometric accuracy in orthorectified imagery products obtained from IKONOS Geo Ortho Kit Imagery. Two dimensional Root Mean Square Error (RMSE2D) is computed and utilized as accuracy indicator. The ancillary data were generated by high accuracy methods: (1) Check (ICPs) and control points (GCPs) were measured with a differential global positioning system (DGPS) and, (2) a digital elevation model (DEM) with grid spacing of 5 m derived from digitized contour lines with an interval of 10 m and extracted from the 1:10,000 Andalusia Topographic Maps series (RMSEz<1.75 m), was used for image orthorectification process. Four sensor models were used to correct the satellite data: (1) First order 3D rational functions without vendor image support data (RFM1), (2) 3D rational functions refined by the user with zero order polynomial adjustment (RPC0), (3) 3D rational functions refined by the user with first order polynomial adjustment (RPC1), and (4) the 3D Toutin physical model (CCRS). The number of control points per orthorectified imagery (9 and 18 GCPs) and their distribution (random and stratified random sampling) were studied as well. The best results, both in the phase of sensor orientation (RMSEO about 0.59 m) as in the final orthoimages (RMSEORTHO about 1.25 m), were obtained when the model RPC0 was used. Neither a large number of GCPs (more than nine) nor a better distribution (stratified random sampling) improved the results obtained from RPC0.

An integrated model to estimate the accuray of digital orthoimages from high resolution satellite imagery

Fernando J. Aguilar, Manuel A. Aguilar, Fernando Carvajal Ramírez, Francisco Agüera Vega,


Revue Française de Photogrammétrie et de Telédétection. ISPRS Commission Technique I, Symposium, nº 184: 11-16



In this work, a theoretical-empirical model has been developed for the modelling of the local geometric accuracy of digital orthoimages from panchromatic QuickBird Very High Resolution Satellite Imagery (VHRSI). The empirical component integrates the error of sensor orientation and its propagation to the orthoimage generation process. The theoretical component, mainly a geometrical study from QuickBird Image Metadata File, seeks to model the propagation of DEM error throughout the orthorectificacion process in addition to the previous errors of the bundle adjustment. For the goal of model developing and calibration, a panchromatic QuickBird Basic Imagery was acquired on 19 December 2004, registering a mean collected GSD of 0.62 m, off-nadir view angle of 8.4º and an azimuth and elevation angle of the satellite with respect to the centre of the image of 123.3º and 80.9º respectively. The QuickBird image employed covered an area of 17 x 18 Km over the district of Níjar, located at the North-East of Almería city, Spain. It was centred on the UTM coordinates European Datum ED50 (easting and northing) of 577,848 and 4,087,277 m. The Toutin’s 3D physical model was the selected method to compute the bundle adjustment and so to carry out the sensor orientation using PCI Geomatica OrthoEngine software v. 9.1.7. On this score, 3D coordinates of 124 ground points were measured by means of high precision differential GPS techniques. From the whole set of ground points, a sub-set of 45 ones uniformly distributed was selected for the sensor orientation (GCPs), whereas the remaining 79 were used as independent check points (ICPs) to assess the performance of the developed model regarding to the average error of the final orthoimages. Inasmuch to the results, the empirical component, which takes into account the effect of pointing error and number and accuracy of GCPs on sensor orientation, presented an acceptable fitting to the experimental data, with a regression coefficient R2 = 0.932. The theoretical component also offered good results, observing like the proposed model reproduces with reasonable accuracy the statistical behaviour of the 2D orthoimage errors measured at the 79 ground points checked. The findings obtained in this work could be used as a guide for the selection of appropriate operational parameters in projects related to digital cartography production and updating from QuickBird imagery.