A COMPARISON OF CLOSE-RANGE PHOTOGRAMMETRY USING A NON-PROFESSIONAL CAMERA WITH FIELD SURVEYING FOR VPLUME ESTIMATION

Rapid and accurate volume calculation is one of the most important requirements in many applications such as construction and mining industries. The accuracy of a calculated volume depends on the number of collected points on the object. Increasing the number of measured points undoubtedly requires higher cost and time. On the other hand, collecting surveying points might sometimes be difficult, dangerous or impossible. The aim of this study is to evaluate the close range photogrammetry (CRP) using a non-professional camera for DEM generation in comparison to the traditional field surveying technique (TST). For this purpose, a test area in Deralok hydropower planet site was considered and the process of DEM extraction in both methods was compared. The obtained results showed that although the CRP method in contrast with TST method was more time consuming, however, this method was able to successfully measure negative slops and berms and, consequently, calculated more accurate volume. Moreover, the relative error of 0.2% was reported. * Corresponding author


INTRODUCTION
The volume calculations are an important requirement of the construction and mining industry (Fawzy 2015).The accurate volume estimation is important in many applications, for example, dam project, road project, and building applications (P.L. Raeva 2016).The traditional methods such as the trapezoidal method, traditional cross sectioning, and improved methods (Simpson-based, cubic spline, and cubic Hermite formula) have been used in volume computing.The main elements of these methods are to collect the points that appropriate distribution and density (M.Uysal 2015).These methods need more mathematical processes and take more time.Although, the high accuracy dependent on the number of collected points on the object(Karami 2014).More points require higher cost and time.In addition, collecting surveying points might be difficult, dangerous or impossible sometimes.(C.Arango 2015) Therefore, the classic surveying method is not always applicable to calculate excavation volume.
There are high accuracy requirements as far as heights are concerned due to volume calculations and therefore high resolution images.However, very precise terrestrial measurements could be extremely time-consuming process.On the other hand, by photogrammetric techniques, large areas can be covered in high details in less than an hour.(Patikova 2004) In comparison to classical geodetic methods, close range photogrammetry is an efficient and fast method.It can significantly reduce the time required for collecting terrestrial data.The accuracy of the volume calculation is proportional to the presentation of the land surface.The presentation of the surface, on the other hand, is dependent on the number of coordinated points, their distribution, and its interpolation.(Yilmaz 2010) The estimated accuracy of the comparison is up to 3% -4%.In some countries, the legislation states that the volume should be calculated with a precision of ±3% of the whole material (P.L. Raeva 2016).However, this value depends on many factors such as the type of material being excavated in the quarry, the atmospheric conditions, etc. (M.Mazhdrakov 2007)

STUDY AREA
The study site is situated in the power house excavation of Deralok Hydropower Plant project in Iraqi Kurdistan and is located 80 kilometres northeast of Dohuk and the area is more than 1 hectare (lon 43.6562 °, lat 37.0689 °).(Figure 1).

METHODOLOGY
Volume calculation is usually performed in two main steps: data acquisition and volume estimation.Time, cost and accuracy are very important parameters in volume estimation techniques.In this paper, the close range photogrammetry (CRP) using a nonprofessional camera and the traditional field surveying technique (TST) have been executed for estimation the volume in a sample project.In the following section, the details of these steps for both methods are described.

Data Acquisition
Data acquisition is an important step for volume estimation.The more accurate the collected data results in more accurate the estimated volume.
For the data acquisition in the field surveying method, a Leica TS-09 total station, with the specifications 1" angular accuracy and Enhanced measurement accuracy to prism 1.5 mm + 2 ppm was used and all the necessary points to estimate the volume were observed.In this case, around the excavation area with a prism and surveying characteristics break lines many points have been observed and, surveying trench wall with the total station non-prism tool was done.
In the CRP method a non-metric camera was used.We have been trying to use the camera at low prices with a high efficiency.The Table 1 shows the camera specifications.
For the study area, we walk around the power house excavation top of the trench and acquired 3-6 images in each station in differed view for increase overlap (Figure 2).
Figure 2. Camera locations and image network

Volume Estimation
To estimate the volume excavation many methods can be used.I.e.trapezoidal method for rectangular or triangular prism, Simpson's and improve methods using Simpson-based, cubic spline and cubic Hermite formula used for conventional method calculation (M.Yakar 2008).

Volume Estimation in TST Method
After obtaining the field data with the TST, the data was export to the TST with flash memory and saved in .idxformat, after editing point and create a .txtfile, this point is ready to import into Civil 3D software.
After import data, we fit a surface to points.In this step, editing the surface is an important step in volume computing because as long as we do not have a correct surface with all break lines, and etc. we cannot compute a correct volume.Figure 3 shows the flowchart of the volume calculation using Civil 3D software.

Volume Estimation with CRP Method
To obtain the values of the excavation volume, we adjust the image first with the GCP, these points was the same georeferenced points around and into the excavation that we survey by TST, after that, we use AgiSoft software to process image, to generation an exact DSM we following this steps:

RESULTS & DISCUSSION
Figure 4 show the number of images that cover the study area, as we see all of the excavation bottom, trench wall, berms exist in more than 9 Photos.

Comparison of excavation Volumes
In this study, the traditional method with TST to estimate volumes of excavation were compared with CRP, data from the same site were taken and the post processing was done in civil 3D with a DEM that generated by AgiSoft with TST.
In this comparison, because we do not have the actual value of the volume excavated, our goal was to compare these two methods together only values compared and examine how close the numbers obtained.

Time spent & cost for data acquisition
The Table 1 shows a clear difference between the two methods of data collection, the CRP is about 3.5 times faster than the TST, in addition, the risks of obtaining the data with the camera are much lower, this because people are not exposed to unstable locations.

Table 2. Time comparison between both methods
Following CRP method is much less expensive than TST because the method requires fewer people and the device used to rent or buy cheaper.

CONCLUSION
In this study, we evaluated the CRP method using nonprofessional camera to generate excavation DEM in comparison to traditional field surveying method.We get 121 images around the study area and applied 23 control and check points.
The volume that obtained by the traditional method and CRP was 198424.48m 3 and 198047.29 m3, respectively.The relative error of 0.2% can conclude that the estimated volume using CRP data was more accurate.The ability of the CRP method in considering negative slope due to loss right in the trenches, which cannot be measured by TST method, was promising.

Figure 1 .
Figure 1.Deralok hydropower planet site, red boundary is power house

Figure 4 .
Figure 4.Camera locations and image overlapIn order to images georeferencing and assess the geometric accuracy (plane and height), a local network of control and cheek points have been considered according to Figure5, and the coordinates of these points have been reading.

Figure 5 .
Figure 5. GCP locationsBasically, the principles of calculating the volume of an object in any kind of photogrammetric software slightly differ from the conventional methods.Unless a Point Cloud Densification is created.Agisoft output DSM include this negative slope, and TST method cannot modeling this negative slops as shown in Figure6DSM from Agisoft and Figure7shows Civil 3D DEM.After converting the agisoft DSM to DEM the volume was computed.