Latitude and Longitude representation. 

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... analysis is an approach to increase machine capacity and obtain efficient machine utilization. Driver’s performance and field condition affect total operation costs, such as fuel, lubricants and repairs, especially in larger machinery which have higher hourly costs. Another issue that is important in any farm operation and may affect farm machinery is timeliness. This parameter refers to the ability of manager to complete a farm activity at such a time that crop return (quantity and quality) is optimized. Better management strategies to improve planning and scheduling such as motion-and-time study management will reduce peak machinery demand and maintain a more stable machine force on the farm, leading to increase yield and profitability. Insufficient machine capacity may prevent completion of a field operation and create economic penalties. In some cases, the quality of field crops, including grains and hays, or horticultural crops, including vegetables and fruits are affected by the dates of planting and harvesting which represents a hidden cost associated with farm machinery. Therefore, obtaining accurate time record of all activities for a specific machine operation is always the first step in operation analysis. GPS receivers and data loggers can easily generate and store time and position information. The second step is to divide the time recorded into primary and support functions. For example, in a citrus harvesting operation, shaking tree and picking fruits from canopy is the primary function. Support functions include stops, adjustments and cleaning. Each component of operation is expresses as a percent of total field time. GPS mounted equipments and computer algorithms can provide managers with essential information for analyzing machine performance, including effective operation time. The third step is to provide details analysis of the information obtained in the steps one and two. This includes examination of each segment of the operation to determine if the time for any appears to be excessive when compared to average values from reasonably efficient operations. Computer programs such as GIS software can be used to visualize this analysis and make decision for those segments which show the greatest possibility for improving the efficiency of the total operation. Researchers at the University of Florida/Citrus Research and Education Center in Lake Alfred are currently developing such a system. A prototype computer program has been developed to process and analyze raw GPS data collected from individual machine operation. A typical string of GPS data in the standard NMEA format contains several information including, latitude, longitude and time are used in calculating machine travel distance, speed and total field time. Based on these parameters and using mathematical algorithms, time lost and actual operational time can be extracted from total field time. Some of the results are shown in Figure ...

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... was a time when growers invested on expensive farm equipment for the sake of high technology and low energy consumption. Management assumed that sophisticated machinery were always more efficient. While this is true, cutting-edge technologies such as precision agriculture and smart farming can also open a new door for cost-conscious farmers to apply modern management tools to reduce the use of consumable field supplies and improve profit. The increasing costs of farm operations, especially in large scale production persuade producers to invest on reliable methods of cost justification. Since mechanical power is an indispensable part of today’s agriculture, farm machinery should be used to the best possible advantage. Global Positioning System (GPS) provides a promising management tool in this area. As a potential user of GPS data, farmers should know that data collection in general and data analyzing in particular provides an excellent opportunity to analyze the location and operational time of farm machinery for a better field management. The purpose of this article is to illustrate the basics behind GPS data collection, receivers output, data interpretation and georeferenced data analysis. Locating a geographical point on the surface of the Earth is done using a grid or network of latitude and longitude line, superimposed on the surface of earth. Expressing these points on a plane as a systematic representation of all or part of the surface of the Earth is called map projection. Some projections treat the Earth as sphere, ellipsoid or both. The U.S. Geological Survey (USGS) uses several different projections. For GPS technology, the World Geodetic System 1984 (WGS-84) earth model has been adopted. Depending on the projection used, there can be different coordinate systems. The three most used coordinate systems are latitude-longitude (Lat/Long), Universal Transverse Mercator (UTM) and State Plane Coordinates (SPC). Latitude and longitude is the most common way to locate points on the surface of the Earth and are recorded in angular units of degrees, minutes and seconds. Other representations of latitude and longitude coordinate are degrees decimal format and degrees-and-decimal minutes. One second of latitude is equal to about 30 meters on earth and indicates north-south position with ○ respect to the equator ranging from 0 to 90 . Longitude defines east-west position with respect to the prime meridian, ranging from ○ 0 to 180 (Figure 1). UTM is a widely used projection for larger scale maps. Coordinate values in UTM are given in meters with the vertical axis called northing and horizontal axis called easting. SPC coordinates are similar to UTM but are generally in units of feet. It is better that farmers use a uniform coordinate system in order to line up different field maps (yield maps, soil property map, etc) and to be able to overlay various layers of ...

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... Global Positioning system (GPS) is a satellite based navigation system that defines position, velocity and time, (PVT), under any climate condition 24 hours a day anywhere in the world, for free. Originally developed for the military, the USA owns GPS technology and the Department of Defense maintains it. The GPS has made a great evolution in different aspects of our today ’s modern life as well as in agriculture section. Today, a growing number of crop producers are using GPS and other modern electronic and computer equipments and practice precision agriculture. The purpose of this article is to provide farmers with some illustrations of GPS concepts such as coordinate systems and NMEA standards in order to ease the understanding of different GPS applications in agriculture. The GPS system was declared fully operational on April 27, 1995. At least 24 GPS satellites orbit the earth twice a day in a specific pattern, travelling approximately 7000 miles per hour about 12000 miles above the earth’s surface. The satellites are spaced so that they follow six orbital paths, with four satellites in each path as shown in Figure 1. This satellite arrangement guarantees that GPS receiver anywhere in the world can receive signals from at least four of them. The signals are radio waves and travel at the speed of light. It only takes between 65 and 85 milliseconds for a signal to travel from a GPS satellite to a GPS receiver. The GPS receiver collects signals from GPS satellites that are in view and uses triangulation to calculate its position, usually expressed as latitude, longitude and altitude. Since the accuracy of GPS is degraded by several sources of errors such as satellite clocks, satellite orbits, earth’s atmosphere, multipath errors and the receiver itself, methods of improving GPS accuracy are used. The most widely used and accepted method is called differential corrections or DGPS. Three sources of differential correction available to most civilian in the United States are U.S. Coast Guard (known as Nationwide DGPS), local FM signals (user provided) and satellite-based differential corrections (such as WAAS, OmniSTAR, Starfire, etc). Typical position error of original GPS (without correction) is about 100 meter. This error is about 1 to 3 m for NDGPS and 1 to 2 m for WAAS in horizontal direction. Different source of errors as well as classifications of different receivers and purchase considerations has been enlightened in details in AE438 factsheet extension. As general reference GPS applications for farmers and agriculturist GPS receivers with better clocks, more precision mathematical algorithm and less internal noise are more expensive and produce less error. Reading collected GPS data and extracting proper information out of them is easy but requires a basic understanding of the coordinate systems and different data formats. There are several ways to locate a geographical point on the surface of the Earth. The three most used coordinate systems are latitude-longitude (Lat/Long), Universal Transverse Mercatur (UTM) and State Plane Coordinates (SPC). Latitude and longitude is the most common way to locate points on the surface of the Earth and are recorded in angular units of degrees, minutes and seconds. This represents angular distanced calculated from the center of the earth. One second of latitude is equal to about 30 meters on earth. Other representations of latitude and longitude coordinate are degrees decimal format and degrees-and-decimal minutes. Coordinate values in UTM are given in meters with the vertical axis called northing and horizontal axis called easting. SPC coordinates are similar to UTM but are generally in units of feet. Coordinate systems are convertible to each other through some simple calculations or using ready available programs. It is suggested that farmers have a uniform coordinate system in order to line up different field maps (yield maps, soil property map, etc) and to be able to overlay various layers of information. GPS receiver communication is defined within an electrical data transmission standard protocol called The National Marine Electronics Association (NMEA). Most devices and programs that provide real time position information understand and expect data to be in NMEA format. A line of data called sentence or string in NMEA standard includes the entire PVT computed by GPS receiver. Different brands and categories of GPS may use different types of NMEA sentence, but all of the standard sentences always star t with a ‘$’ (dollar) sign at the beginning of the line follows by GP which refers to GPS and a three letter suffix that defines the sentence contents. The data within a single line are separated by a comma and the line ends with a carriage return/line feed sequence and can be no longer than 80 characters. Common NMEA sentences used in agriculture are RMC, GGA and RMB. Table 1 and 2 provides definition of each part of a data line in a GGA and RMC sentence. Once the information about different points of a field is known, parameters such as distance between points, velocity and surrounded area between three or more points can be calculated. It should be noted that for small size areas, surface of the earth can be assumed flat and distance between two points can be calculated using the customary math procedure, however spherical shape of the earth should be taken into account when two points are significantly far from each other. In this case, mathematical representation of earth model should be used. In precision agriculture, GPS data are mainly used in determining some parameters of interests as in yield mapping, soil mapping, field boundary mapping, etc. There are lots of amazing applications for GPS technology on land, at sea and in the air. GPS can be considered as the foundation of several cutting edge researches as in GPS applications for farmers and agriculturist environmental studies, agriculture, aerospace, transportation, marine, military, surveying, recreation and so on. The GPS technology has made possible great developments in agriculture. It is used ...