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//Developing mobile applications using the Mobile SDK
//Using GPS data and devices
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The ArcGIS Server Mobile SDK leverages Global Positioning System (GPS) technology to provide location-awareness to any mobile enterprise application. While most people are now familiar with the term GPS and have some idea of what it is and how it works, it is a large and complicated system. Most GPS consumers use the system they are provided as an enduser application such as in car navigation or locational GPS units, where the system is delivered as a single GPS/mapping application. As GIS applications developers we know the GPS system is separate from the mapping system, and it become our job to integrate them into a seamless（无缝的） application. The ArcGIS Mobile SDK includes several GPS components which have been developed to simplify the work for developers to incorporate GPS into a Mobile mapping Application, while providing access to the detailed GPS properties if needed. To fully leverage the power of the GPS system it is necessary have a good understanding of the system and its associated technologies. The Mobile SDK’s GPS components are contained in a separate namespace within the Mobile Library, and provides three .NET Components as part of the toolbox for designing mobile enterprise applications:
GPS Serial Port Connection
GPS File Connection
GPS Display
ArcGIS Server Mobile SDK 利用GPS技术为任何移动企业程序提供位置提示。 现在大多数的人已经熟悉GPS并对它是什么基于它是如何工作有了一定的了解，它是一个庞大、复杂的系统。多数的GPS用户使用这个系统，他们作为一个终端用户应用程序提供的系统，比如：汽车导航、地点定位等等。这里系统作为一个单独的GPS地图程序交付。作为一个GIS应用程序的开发者，我们知道GPS系统和地图系统是分离的，将他们集成到一个无缝的程序就成为了我们的工作。ArcGIS Mobile SDK 包括若干个GPS组件，他们已经被开发为开发者简化把GPS集成到移动地图程序中的工作，如果需要这个程序将提供通道访问GPS属性的详细信息。为了最大化的开发GPS系统的功能，我们需要对这个系统以及相关的功能有一个很到的了解。 Mobile SDK的 GPS组件包含Mobile类库中一个独立的命名空间， 并提供三个.NET组件作为工具箱的一部分用于设计企业级的移动程序。
GPS Serial Port Connection
GPS File Connection
GPS Display
The Serial Port or File Connection provides the linkage（. 联接2.连接） between the GPS device and your Mobile application. The GPS display component is used to visualize the GPS data on your application's map. To better understand the role GPS technology plays in designing mobile enterprise applications and its integration into the Mobile SDK toolbox it is worth taking a look at the GPS and its associated technologies.
Serial Port 和文件链接提供了GPS设备与你的移动应用之间的连接。GPS display组件是用来将GPS数据在你的程序中的地图上面可视化显示。 为了更好的理解GPS技术在设计企业移动应用的时候扮演的角色和他与Mobile SDK工具箱的集成，应该查看GPS和她的关联技术。
GPS Overview
GPS is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS uses radio signals broadcast from orbital satellites (or "man-made stars") to calculate positions accurate to better than a centimeter with the right hardware. GPS has become a vital global utility, indispensable（必不可少的，必需的） for modern navigation on land, sea, and air around the world.
GPS 概述
GPS是一个基于卫星的导航系统，她是由美国国防部放置到轨道上的24颗卫星组成的网络。 GPS最初的目的是用于军事用途，但是在1980年，政府开始向民用开放了这个系统。GPS使用来自轨道卫星的无线电信号广播来计算使用正确的硬件精确到米级别的位置。GPS已经变成了重要的全球公用事业，对于现代的陆地、海洋、空中导航都是不可或缺的。
The foundation of GPS is receiver trilateration from the measured distances between at least three satellites. To achieve accurate positioning the satellites broadcast their orbital position allowing a GPS receiver to measure the individual distances using the travel time of each radio signal.
There are numerous error sources introduced either as part of the system or from the environment. The autonomous（自治的；独立自主的） (self-contained) GPS system provides accuracies in the order of 5 to
For a more in depth understanding of GPS than what is presented in these topics, the following sources are recommended:
GPS的基础是接受者对来自至少三颗卫星的距离测量进行三边计算。 为了达到精确定位，卫星播放了他们的轨道位置允许一个GPS接受者使用每个广播信号的旅行时间来单独测量他们的距离。
这里有很多的误差源，不是来自系统的一部分就是来自环境。 独立GPS系统提供5到20米的理想精度用于导航和大比例定位。为了提高独立的GPS系统的精度，很多不同的GPS技术是可以获取的，允许用户消除误差和提高精度。
为了更加深入的理解GPS而不是仅仅局限于本主题，下面的资源建议你阅读。
GPS Joint Program Office http://gps.losangeles.af.mil/
NMEA http://www.nmea.org
Trimble GPS Tutorial http://www.trimble.com/gps/index.shtml
National Geodetic Survey (CORS) http://www.ngs.noaa.gov/CORS/
WAAS information from Federal Aviation Administration http://gps.faa.gov/
US Coast Guard Navigation Center http://www.navcen.uscg.gov/
Working with NMEA
Within the GPS industry there is one truly global standard that GPS receivers leverage to report their position information, the National Marine Electronics Association (NMEA) is currently the maintainer and distributor of standards that relate to the marine electronics industry. Today the NMEA 0183 standard is widely accepted as the common protocol reported by GPS receivers. There are many other GPS protocols from a range of vendors（供应商） however in most cases all receivers report both their own proprietary（私有的） protocol and the NMEA 0183 protocol. The NMEA 0183 standard was last revised（修订，修改；复习 vi.复习） in January 2002 and is denoted（.意思是；表示，是…的标志） as Version 3.01.
在GPS工业内，这里只有一个真正的全球标准，GPS接受者使用这个标准来报告他们的位置信息，NMEA是当前这个准则的维护者和销售者，这个标准与海洋电子工业想关联。今天，NMEA0183标准作为通用的报告协议被GPS接受者广泛的接受。 这里还有很多其他的GPS协议，从供应商的范围考虑，在很多情况下所有的接收者报告他们私有的协议和NMEA0183协议。 NMER0183最后的修订在January 2002并被表示为：3.01版本。
The NMEA protocol reports sentences of information specific to the device that is reporting them. The first part of the sentence is defines the interpretation（解释，说明，诠释；(） of the rest of the sentence. Each sentence from a GPS receiver is tagged with a prefix(前缀) ‘GP’ followed by three other characters denoting the type of sentence it is. For example, GPGGA is the GPS sentence for reporting GPS fix information. There are a standard set of sentences for GPS however each vendor can also report their own proprietary sentences as they see fit. It is important to note that the GPS components within the ArcGIS Mobile SDK do not read vendor sentences. All sentences are ASCII text. The NMEA standard calls for the interface speed to be 4800 baud with 8 bits of data, no parity（相等）, and one stop bit. It is important to note that （重要的是要注意）while most GPS receivers adhere（；遵守,坚持；追随,支持） to this it might not always be the case. It is important to understand exactly the settings your GPS receiver is leveraging.
Example NMEA sentence:
$GPGGA,010725.753,3403.4073,N,11711.4305,W,1,04,6.0,370.6,M,-32.5,M,0.0,0000*48
【The NMEA protocol reports sentences of information specific to the device that is reporting them】,句子开始的部分定义了句子余下内容的解释（注释）。 GPS接收者接收的每一个句子都是以“GP”标签作为前缀，跟随者三个其他字符表示句子的类型。 比如：GPGGA是用来报告GPS修复信息的句子。对于GPS这里有一个标准的设置，尽管如此，每一个设备生产商也可以报告他们认为合适的自己属性句子。至关重要的是，ArcGIS Mobile SDK内的GPS组件不读取设备生产商的句子。 所有句子是ASCII文本。 NMEA标准调用的接口速度为4800，以及8位数据的波特率，没有等号，和一个停止块。重要的是要注意，尽管有很多的GPS接收者遵守，坚持这个标准，但是并不是总是这个情况。理解影响你的GPS接收的设置非常重要的。
NMEA句子的例子$GPGGA,010725.753,3403.4073,N,11711.4305,W,1,04,6.0,370.6,M,-32.5,M,0.0,0000*48
Differential GPS（差分全球定位系统）
Differential GPS (or DGPS) systems provide corrections to autonomous GPS positions providing accuracies ranging from
DGPS corrections are disseminated（散布，传播） either in realtime（实时） or by postprocessing（后加工）. Realtime DGPS is achieved by broadcasting the DGPS correction over a radio, satellite, or IP-based medium. Postprocessed DGPS is achieved by storing the DGPS correction in a file or database and processing them against autonomous GPS data collected in the field.
差分全球定位系统修正独立的GPS位置，提供精确的定位范围：从5米到亚厘米级别。DGPS 系统依靠至少一个坐落在一个确定的位置的GPS接收机。DGPS 系统通过测量已知的距离和通过计算得到GPS接收机和每一颗轨道卫星距离之间的差别来计算修正的数值。
DGPS 修正可以通过实时传播或者后加工传播。 实时DGPS 通过一个无线电、卫星或者基于IP手段等接收。后加工DGPS接收通过存储DGPS修正到一个文件或者数据库，让他们自己处理在野外收集的GPS数据。
Realtime DGPS is ideal for applications in the field that require high accuracy to navigate to features or re-position them on the fly. However, for applications that require the highest possible accuracy it is ideal to use Postprocessed DGPS. This ensures that the likelihood（可能，可能性） of all GPS positions being differentially corrected is high, as often in the field realtime DGPS can be patchy（斑驳的, 不调和的, 不完整的, 拼凑的） as a result of poor communication coverage to the DGPS source, and also removes any latency（潜伏期） in the processing of the positions that occurs in realtime. This is critical to ensuring the most accurate data possible for your GIS.
对精确要求很高的导航或者在飞行重定位，运行的野外的程序来说，实时的DGPS是很理想的。尽管如此，对于要求尽可能高精度的程序来说，使用后处理DGPS是理想的选择。这能确保所有的GPS位置差分修正比较高的可能性，就像在野外经常，实时DGPS可以拼凑作为沟通不良覆盖DGPS数据源的结果，并移除在处理发生在实时的位置的潜伏期。这对保证你的GIS最高精度数据是非常重要的
GPS Systems
GPS and GIS Since the early
GPS和GIS从早在90年代,GPS已经作为一个工具用来管理一个GIS的精度和质量。 理解你的mobile部署的目的和满足你最需要的GPS技术之间的关系是至关重要的。这里有三种主要的GPS解决方法应用在今天的GIS市场，他们针对：导航，数据收集，调查。 每一种类型的GPS解决方案设计用来满足一个特定的需求：
Navigation Systems
provide low-accuracy and lost-cost solutions ideal for location-enabling a mobile application
为定位的移动程序提供低精度和低成本的理想解决方案。
Data Collection Systems
provide accurate and professional solutions ideal for ensuring the accuracy of your GIS data layers
为确保你的GIS数据图层的精度提供精确的、专业的理想解决方案。
Survey Systems
provide highly-accurate and high-cost solutions ideal for ensuring the accuracy of your critical-GIS data layers
安全系统
提供高精度、高成本的解决方法用于保证你的重要的GIS数据层的精度。
Specific markets require different GPS systems and accuracy needs. The following section outlines（描述） how GPS accuracy is achieved and the types of GPS systems common in the market today. The above three factors play the core role in differentiating the GPS systems. Those that provide the highest accuracy often cost the greatest due to the research and development needed build systems to achieve such accuracies. Data collection systems provide ideal method for collecting new GIS data in the field and taking existing data out into the field and updating the accuracy. While other less costly systems can be used for navigation sucessfully, even though they do not produce highly accurate measurements.
特定的市场要求不同的GPS系统和精确需求。下面的章节描述了GPS精度是如何达到的和今天市场上通用的的GPS系统的类型。 上面的三个因素在区分GPS系统扮演着重要的角色，这些提供最高精度通常消耗也是巨达的，这归因于搜索和创建系统需要的开发，来达到如此的精度。 数据收集系统提供了理想的方法用于在野外收集新的GIS数据，将已有的数据携带到野外以及更新精度。其他低消耗系统可以被成功应用到导航，尽管他们不生产高精度的测量
GPS Accuracy and Yield
The accuracy and yield of a GPS system is determined by a number of factors. Depending on the needs of your application you should to take into consideration the hardware capabilities, DGPS availability, and environmental factors when selecting a GPS system.
The rule of thumb is that higher quality GPS receivers generate more accurate GPS positions. In most cases this is the result of more advanced technology being employed to receive GPS signals, process the GPS signals, and also protect the GPS receiver from any interference. Data collection and Survey systems often employ these technologies to ensure they generate the most accurate GPS positions possible. Navigation systems often leverage lower quality GPS receivers to ensure their price point is ideal for the mass market. The trade off is that these systems are not ideal for collecting data at small scales but are well suited to providing in car and foot based navigation solutions.
GPS的精度和GPS的产量是由一系列的因素影响的。基于你应用程序的需要，在选择一个GPS系统的时候，需要考虑硬件的能力、DGPS的有效性和环境因素。
经验法则是，高质量的GPS接收器生成高精度的GPS位置。 在很多情况下，这是由于很多先进的技术应用到接收GPS信号，处理GPS信号和保护GPS接收器不受任何外界的干扰。 数据收集和测量系统经常使用这些技术来确保他们生成精度最高的GPS位置的可能性。 导航系统经常使用低质量的GPS接收器来保证他们的价格对于巨达的市场是理想的。它的代价就是这些系统不是适合于小比例尺下数据的收集，但是对于汽车导航和徒步的导航是非常合适的。
Leveraging(Leveraging) a DGPS solution increases the accuracy of the GPS positions dramatically. As outlined earlier autonomous GPS although much greater in accuracy than any other position system available in the past still carries a lot of error inherent in the system. Differential GPS removes the majority of this error and can result in major improvements to the accuracy of the GPS positions. The majority of GPS systems in every market look to leverage DGPS today. The Data collection and Survey systems often provide both realtime and Postprocessed DGPS to ensure the greatest possible accuracy, whereas（.然而，但是，尽管） the Navigation systems employ only realtime DGPS as an added benefit in the field.
凭借DGPS解决方案，戏曲性的提高了GPS位置的精度。就像先前描述的那样，独立的GPS尽管在精度上比以往任何可以获取的位置系统都要高，但是她仍然有一从系统中继承的错误。DGPS移除了大多数的错误，结果，GPS位置的精度有一个很大的提高。今天，每一个市场的主要GPS系统都是DGPS. 数据收集和测量系统经常提供实时和后处理的DGPS来保证最大可能的精度。然而导航系统仅仅应用了实时DGPS作为添加的优势。
Environmental influences can degrade(降级) the accuracy of a GPS position. Higher quality GPS receivers employ more advanced mitigation（缓和, 减轻, 镇静） techniques ensuring the best possible GPS positions by filtering out poor signals. The trade off with mitigating GPS signals is that it can reduce the positional yield. If your applications requires high accuracy mitigating signals is beneficial, however if the converse is true then accepting poor signals will ensure best possible yield. The Data Collection systems provide the flexibility to operate in either mode. Generating highest possible accuracy by filtering out poor signals or best yield by accepting all signals when accuracy isn’t critical or when getting a position is more important than no positions. Navigation systems are typically tuned to produce the best yield in tough urban canopy environments. Survey systems are designed to provide the highest accuracy possible and as a result produce low yields especially in regions with urban or vegetative canopy. To over come this other more traditional Survey systems relying on optical technologies are employed to generate high accuracy in these environments.
Accuracy or yield is often achieved at the expense of the other. When deciding on the ideal GPS system for your mobile application it is important to first understand what the accuracy and yield requirements are before making a purchasing decision as it can have a huge impact on the success of your mobile deployment.
环境因素可以减低GPS位置的精度。高质量的GPS接收器使用类很多先进的缓和技术通过过滤外部的信息来保证GPS位置最的精度。 缓和GPS信号的代价就是它可以降低位置产量。 如果你的应用程序需要高精度信号有利于缓解，尽管如此，如果相反是真的，那么接收较差的信号将会保证最佳的回报。 数据收集系统提供灵活的运作模式。 当进度不是很重要或者生成一个位置好过没有位置的时候，通过过滤室外的信号或者接受所有的信号生成最高的的精度。Navigation systems are typically tuned to produce the best yield in tough urban canopy environments.测量系统被设计为提供高精度的可能，结果生产的产量非常低，尤其是在都市地区或者植被冠层。要在这边，其他更多的传统测量系统依赖于光学技术被使用来在这种环境下生成高精度。
准确性和收益率往往是牺牲了其他的地方，当决定在你的移动应用中哪个GPS系统是理想的时候，最重要的是在购买设备之前理解要求的精度和收益是什么，因为这对你成功部署移动应用有巨达的影响。
