TOPOGRAPHIC INDICES

Terrain attributes are commonly used to explain the spatial variability of agronomic, pedologic, and hydrologic variables. The terrain attributes studied here (elevation, slope, aspect, and curvature) are estimated readily from digital elevation models (DEMs), but questions remain about how the accuracy and sample spacing of the elevation data affect the estimated attributes. The main objective of this study was to quantify differences in each terrain attribute due to factors affecting DEM accuracy and grid cell size. Three data sources were compared: (i) real‐time kinematic global positioning system (RTKGPS); (ii) satellite‐differentially corrected global positioning system (DGPS); and (iii) U.S. Geological Survey (USGS) 30‐m DEMs. The GPS data from three undulating agricultural fields in northeastern Colorado were interpolated onto 5‐, 10‐, 20‐, and 30‐m grid DEMs. The DGPS and USGS DEMs produced similar elevation differences relative to RTKGPS DEMs, but elevation differences in USGS DEMs were more spatially correlated. Estimates of curvature were highly sensitive to DEM differences and the sensitivity of slope, aspect, and curvature estimates decreased as grid cell size increased. The impacts of DEM accuracy and grid cell size were investigated using correlations between wheat ( Triticum aestivum L.) grain yields and estimated terrain attributes. The highest correlation coefficients were obtained using RTKGPS data, and decreasing the sample spacing or grid cell size below 30 m did not consistently improve the correlations. These analyses on agricultural lands indicate the importance of accurate elevation data for detailed terrain analyses on grid cell sizes of 30 m or less.

This paper presents an adaptive learning method for data fusion in autonomous\ndriving vehicles. The localization is based on the integration of Inertial\nMeasurement Unit (IMU) with two Real-Time Kinematic (RTK) Global Positioning\nSystem (GPS) units in an adaptive Kalman filter (KF). The observability\nanalysis reveals that $i$) integration of a single GPS with IMU does not\nconstitute an observable system; $ii$) integration of two GPS units with IMU\nresults in a locally observable system provided that the line connecting two\nGPS antennas is not parallel with the vector of the measured acceleration,\ni.e., the sum of inertial and gravitational accelerations. The latter case\nmakes it possible to compensate for the error in the estimated orientation due\nto gyro drift and its bias without needing additional instruments for absolute\norientation measurements, e.g., a magnetic compass. Moreover, in order to cope\nwith the fact that GPS systems sometimes lose their signal and receive\ninaccurate position data, the self-tuning filter estimates the covariance\nmatrix associated with the GPS measurement noise. This allows the KF to\nincorporate GPS measurements in the data fusion process heavily only when the\ninformation received by GPS becomes reliably available.\n

Various corrector surface models are proposed to mitigate systematic height errors to fit the orthometric heights determined by combining the Tainan City real-time kinematic (RTK) global positioning system (GPS) network and the local geoid model data to the published orthometric heights. Several data sets for Tainan City were tested and analyzed. Two geometric geoid models and one gravimetric-geometric geoid model were generated using the GPS and leveling data. Consequently, three types of orthometric heights were determined (Models I, II, and III). The selection of the optimal corrector surface model for different models was based on a series of statistical tests. The test results show that (1) the selection of the optimal corrector surface model is highly related to the geoid model generating method, hence the optimal corrector surface models are a fifth-degree polynomial for Models I and II and a seven-parameter similarity transformation for Model III; and (2) the determined orthometric height ...

RTK GPS mapping of transplanted row crops

In this paper, we present a complete set of solutions to detect the location of the autonomous horticulture rover used for precision agriculture purposes during the early growth stage of the crops. The horticulture rover autonomously traverses the furrow by aligning itself with the centerline using the dynamic inversion navigation algorithm. The navigation algorithm takes the cross-track error and heading error of the rover deviating from the centerline as the location input, and outputs the desired left and right track speeds to the control system to correct the rover course. The rover has been using the real time kinematic (RTK) -based global position system (GPS) as the sensor to detect the location of the rover, but satellite signals can suffer from sporadic loss, and the geographical characteristics of the environment need to be accurately mapped beforehand. These limits of RTK GPS drastically increase the work load of the operators and decrease the location detection accuracy of the rover. The proposed easy-to-implement machine-vision based location detection solution set accepts the raw pictures taken by the camera mounted on the rover as input and calculate the cross-track and heading errors of the rover as outputs. It neither requires the usage of GPS, nor acquisition of environmental geographical information beforehand. Our test results indicate that the proposed machine-vision based solution set is able to outperform the RTK GPS by providing the cross-track location and heading information of the rover with an error less than 20% of that achieved by a RTK GPS, when the rover is within the furrow during the early growth stage.

<p>The Wairarapa Fault is a major active dextral strike-slip fault in the southern North Island of New Zealand. It is expressed at the surface as a highly segmented fault trace that occurs ~100-400 m east of the Tararua and Rimutaka Range front, where it cuts Last Glacial Maximum (LGM) aggradation gravels. Along its central section, northeast of the Waiohine River, the Wairarapa Fault progressively displaces a flight of post-LGM degradation terraces incised into the "Waiohine" surface at the top of these gravels. Detailed mapping of the variably displaced fluvial terraces at Waiohine River using a Real-Time Kinematic (RTK) Global Positioning System (GPS) and an Electronic Distance Meter (EDM) was used to produce Digital Elevation Models (DEM) from which, the displacements of terraces, risers and paleochannels could be quantified. The timing of fluvial terrace abandonment by the Waiohine River was constrained from previously published and newly obtained Optically Stimulated Luminescence (OSL) dating of post-abandonment sands and silts that mantle the Waiohine terraces. The cumulative dextral displacements of terrace risers range from 12.4 +/- 0.8 m (2 sigma) for the youngest terrace, to 101.1 +/- 3.4 m (2 sigma) for the oldest terrace (this is the Waiohine aggradation surface). The corresponding cumulative vertical displacements of the treads of these terraces range from 1.3 +/- 0.02 m (2 sigma) to 19.7 +/- 0.09 m (2 sigma). The ratio of horizontal to vertical slip for the seven Waiohine terraces averages 6.9 +/- 3.5 (2 sigma). A comparison between the paleochannel and adjacent riser displacements at the Waiohine terraces suggests that a complete riser trimming model for progressive fault displacements of flights of degradation terraces is most appropriate at this site. Under a complete trimming model, a riser begins recording displacement only after its lower bounding terrace tread is abandoned. We estimate the Late Quaternary dextral slip rate for the central part of the Wairarapa Fault by measuring the lateral offsets and abandonment ages of two terrace-riser pairs. Based on previously published OSL age data, and our new estimated displacement for the Waiohine aggradation surface, we calculate a dextral slip rate of 12.0 +/- 3.5 mm/yr (1 sigma) for the central Wairarapa Fault. The dextral displacement and maximum OSL age determined in this study for the next younger terrace require a minimum dextral slip rate of 7.2 +/- 0.8 mm/yr (1 sigma). We also determine the magnitudes of the inferred 1855 (smallest displacement) and penultimate (next-smallest displacement) single-event displacements at Waiohine terraces, as 12.4 +/- 0.8 m (2 sigma) and 9.7 +/- 1.7 m (2 sigma), respectively, implying a mean co-seismic dextral displacement of 10.6 +/- 2.6 m (2 sigma) at the Waiohine River for the last two earthquakes on the Wairarapa Fault. Previous studies suggest a northward decrease in slip rate, but are inconclusive as to the mechanism by which this decrease is accommodated. By comparing our slip rate and single-event displacement data with results from elsewhere along the fault, we infer that there has been a northward decrease in both long-term dextral slip rate and the mean size of co-seismic dextral displacements. Co-seismic dextral displacements are 10-30 % lower at Waiohine River than on the southern Wairarapa Fault (alongstrike distance of 15-20 km), and 10-50 % lower on the northern section of the fault near Mauriceville than at Waiohine River (along-strike distance of ~35 km). The decrease in Late Quaternary dextral slip rate northwards along the fault is therefore, probably a longer-term expression of such an along-strike reduction in the mean size of co-seismic strike-slip on Wairarapa Fault ruptures. This reduction may have been caused by a slip transfer off of the main fault and onto some combination of the Carterton, Masterton and Mokonui Faults, that splay northeast-ward off of that fault. The surface trace of the central section of the Wairarapa Fault is characterised by a series of left-stepping en echelon fault segments, where deformational pressure bulges have formed in the area of overlap between adjacent discontinuous strands. We mapped the fault and associated deformational surface features through a combination of field mapping and aerial photograph surveys. In addition, we used an RTK GPS to collect detailed topographic data across two particularly well defined pressure bulges, just south of the Waiohine River. Using this quantitative topographic data, we calculated the volumes of these two bulges, and the depths at which the faults bounding these bulges converge into a single fault plane. The near-surface 3D geometry of the Wairarapa Fault is defined by a three-order hierarchy of faults, where the lower two orders of faults are arranged in an en echelon array with respect to the next higher order fault. We define the first-order fault to be the single, northwest-dipping Wairarapa Fault plane that we infer to exist at depth within basement rock. The second-order (Type A) fault segments are defined to be 2-7 km long and separated by stepover widths of 250-350 m. These stepovers are where the largest (Type A) bulges have formed. Our volumetrically calculated fault convergence depth for Type A bulges are ~100-260 m, suggesting that Type A faults converge into a single Wairarapa Fault plane within basement rock, and well below the LGM Waiohine gravels. We infer that the Type A faults and bulges began forming within basement rock prior to Waiohine gravel deposition. The distinctly smaller, third-order (Type B) fault segments are 500-4000 m long and separated by fault stepover widths of 30-150 m. Between these segments, the smaller (Type B) bulges have formed. Our volumetrically calculated fault convergence depths for Type B faults are ~1-18 m, suggesting that the bulges bounding faults converge downwards at or near the base of the Waiohine gravels. The Type B bulges, therefore appear to have formed by distributed deformation of the near-surface Waiohine gravels after they had buried the pre-existing Wairarapa Fault plane in basement. The currently active Wairarapa Fault, located 100-400 m east of the range-front, we infer to be a relatively immature splay that has recently propagated upward through previously unfaulted material from an older Wairarapa Fault at depth, reflecting eastward propagation of deformation into the Wairarapa Valley in response to topographic loading of the Tararua and Rimutaka Ranges. The segmented, discontinuous characteristics of its surface fault zone suggest that the current fault strand is at an early stage of its evolution even at depth in basement, an apparent immaturity that is not simply restricted to the deformation of the surficial Waiohine gravels (e.g. Type B bulges). By reference to the results of previously published analogue models and up-scaling of these results to the dimensions of the natural setting, we qualitatively estimate a finite dextral displacement on the currently active strand of the Wairarapa Fault of between ~130 m and ~1700 m. Together with our new Late Quaternary dextral slip rate estimate for the central Wairarapa Fault, this would seem to imply an age of inception the currently active splay of the Wairarapa Fault in the Wairarapa Valley of perhaps 100-250 ka or younger. In the natural case of the Wairarapa Fault, en echelon fault segments ("R-faults") strike only 2 [degrees]-18 [degrees] (average of ~6-7 [degrees]) with respect to the average strike of the main fault in basement. This angle is much smaller than is modelled in analogue experiments of the deformation of a previously unfaulted overburden above a strikeslip to slightly oblique-slip basement fault (10 [degrees] -30 [degrees]). The width of the fault zone is also much narrower (350 m) for the Wairarapa Fault, than the scaled-up widths of the fault zones produced in these analogue models (1-2 km). These differences are interpreted to reflect the shallow fault convergence depths for the Wairarapa Fault in comparison to those created in the analogue models, which include a thick surficial "overburden" of unfaulted sand. That thick overburden allows the fault at depth to propagate upward as a wide splay-bounded fault zone at the surface. The surface structures along the Wairarapa Fault exhibit a strong plan-view asymmetry that is reflected in the consistently triangular shape of Type A and B pressure bulges and the across-strike asymmetry defined by the geometry of the faults and bulges in profile. Moreover, there is a partitioning of oblique slip components between the two different splays bounding a given pressure bulge along the Wairarapa Fault, where the northwest bounding fault strands exhibit a greater proportion of strikeslip displacement, and the southeast bounding faults exhibit a greater proportion of dip-slip displacement. This asymmetry is interpreted to be a result of the obliquity of convergence and the northwest dip of the master Wairarapa Fault plane at depth.</p>

Network-based Real Time Kinematic (NRTK) GPS positioning is considered to be a superior solution compared to the conventional single reference station based Real Time Kinematic (RTK) GPS positioning technique whose accuracy is highly affected by the distance dependent errors such as satellite orbital and atmospheric biases. NRTK GPS positioning uses raw measurements gathered from a network of Continuously Operating Reference Stations (CORS) in order to generate more reliable error models that can mitigate the distance dependent errors within the area covered by the CORS. This technique has been developed and tested considerably during recent years and the overall performance in terms of achievable accuracies, reliability and mobility is as good as or even better than can be achieved using the conventional RTK GPS positioning technique. Currently, there are several commercial NRTK services around the world. In the United Kingdom (UK), for instance, Leica Geosystems in partnership with Ordnance Survey has been offering a NRTK GPS service since 2006. This service is called SmartNet and it can provide continuous centimetric level of accuracy to its subscribers. However, NRTK GPS positioning is particularly constrained by wireless data link coverage, correction transmission delay and completeness, GPS signal availability, etc., which could downgrade the positioning quality of the NRTK results. The paper presents some preliminary testing results of an investigation of the SmartNet service from the end users' point of view. A snapshot of the service's performance was carried out as part of a recent PhD studentship jointly awarded by the UK's Engineering and Physical Sciences Research Council (EPSRC) and Leica Geosystems (UK) to conduct comprehensive research into NRTK GPS quality control measures at the Institute of Engineering Surveying and Space Geodesy (IESSG), the University of Nottingham. In order to evaluate the service's quality several static and kinematic tests were performed using the same type of equipment and in the same way that the SmartNet subscribers would have used it. Centimetric accuracy was generally attained during both static and kinematic tests. This high accuracy was only affected by some level of unavailability mainly caused by GPS signal blockage. Additionally, the influence of the number of satellites in view, dilution of precision (DOP) and age of corrections (AoC) over the accuracy and stability of the NRTK GPS solution was also investigated during this research and presented in the paper.

Many applications demand high-precision navigation in urban environments. Two frequency real-time kinematic (RTK) Global Positioning System (GPS) receivers are too expensive for low-cost or consumer-grade projects. As single-frequency GPS receivers are getting less expensive and more capable, more people are utilizing single-frequency RTK GPS techniques to achieve high accuracy in such applications. However, compared with dual-frequency receivers, it is much more difficult to resolve the integer ambiguity vector using single-frequency phase measurements and therefore more difficult to achieve reliable high-precision navigation. This paper presents a real-time sliding-window estimator that tightly integrates differential GPS and an inertial measurement unit to achieve reliable high-precision navigation performance in GPS-challenged urban environments using low-cost single-frequency GPS receivers. Moreover, this paper proposes a novel method to utilize the phase measurements, without resolving the integer ambiguity vector. Experimental results demonstrate real-time position estimation performance at the decimeter level. Furthermore, the novel use of phase measurements improves the robustness of the estimator to pseudorange multipath error.

The potential use of a real-time kinematics (RTK) GPS receiver for seed mapping with a high level of accuracywas investigated. High-accuracy seed mapping can potentially be used in weed control and plant-specific crop management.A four-row Salvo 650 vacuum planter was retrofitted with an RTK GPS receiver. Four seed detector sensors (one per plantingunit) were mounted directly above the planter shoes. These sensors detected the seeds as they fell through seed tubes. Twolow-cost single-board computers were used to acquire data in real time and display it in the tractor cab. The first computerwas interfaced to the RTK GPS unit to determine seed location and forward speed. The second computer was interfaced toa display unit mounted in the cab. The first computer obtained the GPS time and UTM coordinates every second and storedthem with a reference time (time tag). This computer also monitored the seed detector sensors, time-tagged the seeds fromeach unit, and stored the information in memory. The second computer monitored the first computer and reported the plantersperformance through the display unit mounted in the tractor cab. Field tests were conducted to check the performance of thisplanter over two growing seasons. The first year test results indicated a need to control the sensitivity of the seed detectorsensors used for seed detection. The second year tests showed that the improved system performed very well. The differencesbetween the actual plant and the seed map generated by the RTK GPS based planter were in the range of 30 to 38 mm.

Stockpiles are accumulations of materials such as coal or ore stored at specific locations. Accurate stockpile volume measurement is crucial in the mining and logistics industries for inventory management and cost efficiency. Conventional methods like Real-Time Kinematic (RTK) GPS rely on surface coordinate measurements but require numerous points, especially for irregular-shaped objects. Newer technologies like Terrestrial Laser Scanners (TLS) offer high-precision alternatives by capturing thousands of points per second, expediting and enhancing the resolution of volume measurements. This study compares TLS and RTK GPS methods in measuring the volume of andesite rock stockpiles at PT Bara Tabang. This research uses a quantitative approach, involving six Ground Control Points (GCPs) measured using the Sokkia GRX2 RTK GPS on October 24, 2024. TLS generated over 8.6 million point cloud data filtered down to 35,197 points, while RTK GPS yielded 2,276 coordinates. Accuracy testing showed very small RMSE values (RMSEr: 0.008 m; RMSEz: 0.007 m), and both LE90 and CE90 demonstrated 90% confidence within a 0.012 m range. Volume calculation using Surpac software with the cut and fill method showed TLS produced a volume of 18,766 bcm (51,982 tons/m³), while RTK GPS resulted in 18,694 bcm (51,782 tons/m³), with a difference of 72 bcm or 0.211%.These results indicate that both methods offer acceptable accuracy; however, TLS provides greater data density, efficiency, and precision, particularly for complex or large-scale stockpile objects. Therefore, TLS is recommended for high-accuracy volume measurement in mining operations that require efficiency and detailed analysis.

This paper demonstrates the performance of a fixed-wing unmanned aerial vehicle in mapping semi-undulated area. Current practices incur huge cost and time consuming. The aim of this study is to evaluate photogrammetric technique for mapping slope. Fixed-wing unmanned aerial vehicle (UAV) was employed as a tool for image acquisition at the height of 300m. This unit is a complete package that includes low cost digital camera, autonomous chip, global positioning system (GPS), gyro and electronic speed controller. This study was conducted at Skudai, Johor, which is located approximately at latitude 1°33'24.49N and longitude 103°39'4.30E. All the acquired images were processed using photogrammetric technique which comprise of aerial triangulation and bundle adjustment. There are two main photogrammetric products produced from this study known as digital orthophoto and digital elevation model (DEM). Both products were analyzed to determine accuracy of the results. Ground control points and check points were distributed randomly at the study area and all the points were established using GPS Real Time Kinematic (RTK) technique. Based on the results, it was found that root mean square error for slope analysis is +1.169m and length analysis is +0.259m.

Because spatial yield variability is usually related to topographic features, the availability of an accuratetopographic map should provide an opportunity to improve management of agricultural inputs. The objective of this studywas to develop a topographic map using a submeter accuracy differentialcorrected global positioning system (DGPS) andelevation data collected during routine crop management passes throughout multiple years. Two fields (24 and 31 ha) witha relief of 19 to 23 m were selected for this study. Elevation was obtained on 1s intervals using a RealTimeKinematic (RTK)GPS mounted on a pickup truck and driving passes on 3 to 50m intervals (greater distances for relatively uniform areas).Elevation was also obtained from multiple (six to seven) passes (4 to 14m intervals) with a DGPS mounted on a tractor,sprayer, or combine (1 or 2s intervals). Elevation data were interpolated to a 5m grid. Mean elevation from everycombination of passes with the DGPS was compared to elevation from the RTK GPS using the root mean square error (RMSE).A simple linear regression was used to compare the average elevation from the DGPS (based on all passes) to the RTK map.Threedimensional wireframe surfaces developed from the RTK GPS and DGPS data and several transects across thesesurfaces were used to evaluate the success of using the DGPS data. The RMSE decreased from 0.63 and 0.75 with one pass,for Fields One and Two, respectively, to 0.39 with six and seven passes, respectively. Average elevation, as determined fromsix or seven passes with the DGPS, was linearly related to elevation from the RTK GPS (r2 > 0.99). Although absoluteelevation differences were sometimes > 1 m, the DGPS maps were effective in characterizing the dominant topographicfeatures of both fields. Features as small as terraces, which are probably smaller than a typical manageable unit, were evidentin the DGPS topographic map. Agronomically important topographic features were identifiable with a DGPS.

Watershed planning is a major issue in Turkey and other parts of the world. Surrounded by seawater on almost three-quarters of its international borders and by sheer mountains along the coastal regions and throughout the country, Turkey experiences a range of climatic changes, which constantly shape its topography. Recently, the occurrences of floods, landslides, and torrents have increased, forcing decision-makers to come up with solutions to manage and rehabilitate the upper watersheds in order to stop or limit the impact of disasters on downstream areas. Possible solutions should reduce flow coefficients, erosion, and sedimentation and increase reservoir capacities. It is expected that torrent volumes will decrease, drainage regimes on slopes will be better organized and adjusted, thawing snow will be better deposited and delayed, evapotranspiration will increase, surface runoffs will be delayed, and water regimes will be better managed, meaning that flood and torrent control will be achieved. For the reasons mentioned above, watershed parameters need to be firmly set. In the scope of this study, the elevation, slope acreage, and reservoir capacity of a small watershed, as extracted from open-access elevation models, were compared to a real-time kinematic (RTK) global positioning system (GPS)-generated point cloud and the resulting elevation model through various geospatial and analytical means. The Shuttle Radar Topography Mission (SRTM) C-band digital elevation model (DEM) (version 3) proved to be a satisfactory method in making residual, correlation, mean, and reservoir capacity comparisons. An L-band Advanced Land Observing Satellite (ALOS) phased-array-type synthetic aperture radar (PALSAR) and an X-band DLR_SRTM ASTER were slightly superior methods in terms of defining a greater number of slope categories than the other models. Finally, DLR_SRTM and SRTMv3 could match a greater number of slope façades than the other models. Seventeen years after its acquisition, SRTM and its derivatives have continued leading the topographic definition of the Earth.

An adaptive turning algorithm for a four-wheel robot tractor in the headland is presented in this paper. The navigation sensors consisted of an inertial measurement unit and a real-time kinematic global positioning system (GPS). An objective function based on weights was used to create the navigation path, connecting by continuous primitives. The asymmetric steering mechanism was then taken into consideration with a vehicle model. To follow the path accurately, the slide movement of the robot and the steering rate were taken into account by estimating the turning radius in real time. In addition, the vehicle model was tuned based on the results of each turn. Therefore, the turning control algorithm was optimized on the basis of the specific conditions in the field. Field experiments showed that the robot tractor approached the next path with an average lateral deviation of 3.9 cm at a speed of 1.2 m/s during a turn. Compared to a conventional turning scheme, the time consumption and turning trajectory were decreased by 17% and 21%, respectively. Keywords: autonomous tractor, path planning, dynamic circle-back turning, switch-back turning, robot tractor, reinforcement learning DOI: 10.25165/j.ijabe.20181106.3605 Citation: Wang H, Noguchi N. Adaptive turning control for an agricultural robot tractor. Int J Agric & Biol Eng, 2018; 11(6): 113–119.

The radio frequency identification (RFID) technology has proven its potential in locating and tracking construction resources, a critical task in construction project control. However, the main challenge is how to achieve desired levels of locating accuracy. This paper presents an enhanced boundary condition method that incorporates the tag-reader angle and the reader geometric configuration factors to control the accuracy of a locating system that integrates RFID and real time kinematic (RTK) global positioning system (GPS). Controlled laboratory experiments were conducted to assess their effects and create quality control filters. This study demonstrated the relationship between the detecting range and the tag-reader angle and used it to separate valid/invalid boundary points. Spatial dilution of precision (SDOP) was formulated to measure the geometric configuration of readers forming the boundary constraint. Correlating SDOP to the locating error through a polynomial regression model, a mechani...