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為農(nóng)業(yè)機(jī)械提供位置數(shù)據(jù)測(cè)量 Herman Speckmann 原文來源:Federal Agricultural Research Centre Braunschweig (FAL), Institute for Biosystems Engineering, Bundesallee 50, D-38116 Braunschweig, Germany 摘要 農(nóng)業(yè)機(jī)械、車輛需要位置數(shù)據(jù)來指導(dǎo)和控制執(zhí)行最佳工作位置。位置數(shù)據(jù)也被需要用在像精細(xì)農(nóng)作這樣的應(yīng)用上。位置數(shù)據(jù)的必要的準(zhǔn)確性、分辨率和頻率依照不同的應(yīng)用而變化。只有一個(gè)系統(tǒng),安裝在中央車輛(例句、拖拉機(jī)),應(yīng)該提供對(duì)每項(xiàng)任務(wù)的位置數(shù)據(jù)。 提出的關(guān)于中央系統(tǒng)的基本概念是位置數(shù)據(jù)按照特定應(yīng)用程序計(jì)算并且直接被傳送到它需要被應(yīng)用到的那個(gè)點(diǎn)上。這片論文闡述了測(cè)量的基本原理和位置數(shù)據(jù)的計(jì)算，還對(duì)現(xiàn)有的傳送數(shù)據(jù)的農(nóng)業(yè)網(wǎng)絡(luò)進(jìn)行了簡(jiǎn)要介紹。它集中建議了一個(gè)提供和轉(zhuǎn)移位置數(shù)據(jù)的網(wǎng)絡(luò)服務(wù)。被討論的解決方案是以農(nóng)業(yè)BUS（總線）系統(tǒng)為基礎(chǔ)(DIN 9684, ISO 11783). ? 2000 Elsevier Science B.V. 版權(quán)所有. 1.前言 位置指導(dǎo)的目的是給生長(zhǎng)在農(nóng)田里一個(gè)固定的區(qū)域上的莊稼帶來增產(chǎn)的方法。莊稼或者它們?cè)谵r(nóng)田里所處的位置是指導(dǎo)的重要參照。 位置數(shù)據(jù)被用來指導(dǎo)農(nóng)用車、實(shí)現(xiàn)控制和支持精耕農(nóng)業(yè)。準(zhǔn)確性、分辨率和頻率取決于他們的具體應(yīng)用。 必須強(qiáng)調(diào)的是本文沒有合適的解決這個(gè)問題的傳感器來產(chǎn)生數(shù)據(jù)。更確切的說,這里研究的問題是參照移動(dòng)單位的一定的位置進(jìn)行了一個(gè)位置信號(hào)產(chǎn)生,但是這個(gè)位置和需要的位置數(shù)據(jù)并不是完全一致的。此外，位置信息有可能在同一時(shí)間被需要用于幾種目的， 車輛和工具組合的結(jié)構(gòu)可能會(huì)經(jīng)常改變。 正如 Freyberger 和 Jahns (1999), Wilson (1999)所提到的， 測(cè)量系統(tǒng)可以是一個(gè)絕對(duì)定位系統(tǒng),比如Bell(1999)描述的衛(wèi)星系統(tǒng)，或者是一個(gè)相對(duì)的系統(tǒng)，比如Debain et al. (1999), Hague et al. (1999)描述的機(jī)器視覺系統(tǒng)。它可能也包括輔助傳感器。 傳感器只有在參考具體位置情況下測(cè)量位置，比如相機(jī)的安裝點(diǎn)、天線的底部。在接下來的描述中，這個(gè)位置被稱為測(cè)量點(diǎn)。由于各種原因,這位置測(cè)點(diǎn)的是預(yù)先設(shè)定好的，意味著衛(wèi)星天線將盡可能安裝在拖拉機(jī)的車頂上以便減少測(cè)量不到的區(qū)域。攝像機(jī)將會(huì)安裝在有保障最佳視覺的位置。粗糙或傾斜的表面引起的運(yùn)動(dòng)可能導(dǎo)致測(cè)量位置和運(yùn)動(dòng)表面的位置不同。例如，一輛車頂上裝有衛(wèi)星天線的車輛，大約3.5m，駕駛在10°的斜坡表面，傾斜方向造成的區(qū)別相差60cm。圖1闡述了這個(gè)情形。在這個(gè)例子中，計(jì)算一個(gè)參考點(diǎn)的位置可能更適當(dāng)一些。貝爾(1999)提出把拖拉機(jī)的后方軸的中點(diǎn)作為參考點(diǎn)。表面上的一個(gè)點(diǎn)，例如，后方軸中間的下垂直面似乎顯得更適合與某些應(yīng)用。像一些應(yīng)用，比如控制實(shí)現(xiàn)，工具的一定點(diǎn)的位置可能最終重要。這個(gè)點(diǎn)將被稱作目標(biāo)點(diǎn)。 在某些情況下位置數(shù)據(jù)需要用于不同的目的，分別為每個(gè)目的以一種獨(dú)立的測(cè)量系統(tǒng)測(cè)量位置不是很有效。當(dāng)位置測(cè)量只有一次時(shí)多個(gè)硬件可以避免,同時(shí)工具上其他點(diǎn)的位置或者工具也被計(jì)算。假如位置和方法被測(cè)量，實(shí)驗(yàn)測(cè)量和空間向量之間的地點(diǎn)測(cè)點(diǎn)的計(jì)算是眾所周知的，那么這種情況是可能的。如果兩個(gè)點(diǎn)嚴(yán)格耦合,這意味著兩點(diǎn)都在拖拉機(jī)上、兩點(diǎn)之間的向量是常數(shù),一個(gè)簡(jiǎn)單的矩陣運(yùn)算就能產(chǎn)生結(jié)果。如果這些點(diǎn)沒被嚴(yán)格耦合,這意味著,例如,一處拖拉機(jī),另一個(gè)是在附加工具上，矢量是可變的。額外的測(cè)量成為必要用來建立兩點(diǎn)之間的向量或必須應(yīng)用其他原理計(jì)算目標(biāo)點(diǎn)的位置。 2.數(shù)據(jù)處理和數(shù)據(jù)轉(zhuǎn)移 通過計(jì)量點(diǎn)上的測(cè)量位置和方法，在車輛或工具上任何點(diǎn)的位置數(shù)據(jù)可以被計(jì)算出來。計(jì)算結(jié)果可以被測(cè)量系統(tǒng)(中央數(shù)據(jù)處理)或由請(qǐng)求目標(biāo)位置數(shù)據(jù)的各個(gè)系統(tǒng)(分布式數(shù)據(jù)處理)計(jì)算出來。 2.1 分布式數(shù)據(jù)處理 在分布式數(shù)據(jù)的情況下，測(cè)量系統(tǒng)僅作為智能傳感器服務(wù)。它測(cè)量需要的位置和計(jì)算，和提供這些未經(jīng)處理的數(shù)據(jù)。頻率和精度等特點(diǎn)取決于請(qǐng)求的單位。這個(gè)單位執(zhí)行所有處理來計(jì)算位置。單位必須知道測(cè)點(diǎn)的位置和各有關(guān)參數(shù)。這樣處理的好處是測(cè)量裝置可以相對(duì)簡(jiǎn)單。另一方面,每個(gè)請(qǐng)求的單位需要的充分的能力來履行這一運(yùn)算。 2.2 中央數(shù)據(jù)處理 測(cè)量單位被擴(kuò)展包括計(jì)算目標(biāo)位置的各個(gè)組件。這個(gè)測(cè)量和處理系統(tǒng)形成了一個(gè)所謂的位置和導(dǎo)航服務(wù)的單元，這個(gè)單元提供任何目標(biāo)點(diǎn)的最終位置數(shù)據(jù)。在這種情況下,只有一個(gè)測(cè)量與處理系統(tǒng)是必要的，即使位置數(shù)據(jù)必須被更多的用戶要求。這樣做，只有PNS必須知道所有相關(guān)的參數(shù)來進(jìn)行計(jì)算。 2.3 數(shù)據(jù)傳送 無論數(shù)據(jù)在哪里處理，一個(gè)數(shù)據(jù)傳輸是必要的。對(duì)于這樣一個(gè)數(shù)據(jù)傳輸，一個(gè)標(biāo)準(zhǔn)的網(wǎng)絡(luò)是適當(dāng)?shù)摹榱擞糜谵r(nóng)業(yè)領(lǐng)域,存在一個(gè)在移動(dòng)單位和固定農(nóng)場(chǎng)電腦之間傳輸數(shù)據(jù)的汽車。農(nóng)業(yè)總線系統(tǒng)(LBS)也已被標(biāo)準(zhǔn)化以便能在網(wǎng)路的各個(gè)電子單元（LBS節(jié)點(diǎn)或BUS節(jié)點(diǎn)）之間進(jìn)行信息交換。這個(gè)標(biāo)準(zhǔn)定義了物理層網(wǎng)絡(luò)，網(wǎng)絡(luò)協(xié)議，系統(tǒng)管理，數(shù)據(jù)對(duì)象和常見任務(wù)的服務(wù)程序（Speckmann andJahns, 1999）。 LBS以DIN9684(DIN,1989–1998)作為標(biāo)準(zhǔn)。目前,正在努力建立一個(gè)國(guó)際標(biāo)準(zhǔn)(Nienhaus,1993)，ISO 11783，為了這個(gè)目的，像LBS，ISO 11783也將定義一個(gè)農(nóng)業(yè)BUS作為一個(gè)農(nóng)業(yè)機(jī)械交換數(shù)據(jù)的開放系統(tǒng)，特別是在拖拉機(jī)-執(zhí)行工具的組合和從移動(dòng)單位到靜止不動(dòng)的農(nóng)場(chǎng)計(jì)算機(jī)。這個(gè)標(biāo)準(zhǔn)是基于控制器區(qū)域網(wǎng)絡(luò)數(shù)據(jù)協(xié)議(CAN; BOSCH, 1991)。市場(chǎng)上有相應(yīng)的硬件設(shè)備。 在LBS中,為一般位置數(shù)據(jù)(地理位置:經(jīng)度、緯度、高度,或軌道位置)的傳輸定義了數(shù)據(jù)對(duì)象。這標(biāo)準(zhǔn)允許定義的額外的數(shù)據(jù)對(duì)象,例如多維的距離，方向和速度。沒有幾何實(shí)施參數(shù)的數(shù)據(jù)對(duì)象目前存在在LBS中。ISO 11783提供，在第7部分(信息實(shí)現(xiàn)應(yīng)用層），實(shí)施航行偏移的第一個(gè)定義?，F(xiàn)行標(biāo)準(zhǔn)沒有定義數(shù)據(jù)在哪里進(jìn)行處理。因此，關(guān)于BUS中哪個(gè)單元計(jì)算目標(biāo)點(diǎn)的數(shù)據(jù)，哪個(gè)或那些單元測(cè)量數(shù)據(jù)不具體。 LBS提供所謂的LBS服務(wù)來執(zhí)行常見任務(wù)。LBS服務(wù)是為L(zhǎng)BS的參與者頻繁地執(zhí)行復(fù)發(fā)的任務(wù)的功能單元。LBS用戶站就是這樣的一項(xiàng)服務(wù)。這是一個(gè)為用戶提供輸入和輸出BUS上節(jié)點(diǎn)(BUS參與者)處置的數(shù)據(jù)中央接口。另一項(xiàng)服務(wù)提供在移動(dòng)單位和固定的電腦，農(nóng)場(chǎng)的電腦之間的數(shù)據(jù)交換。一些服務(wù)在LBS中被定義但尚未有詳細(xì)的標(biāo)準(zhǔn)，例如診服務(wù)斷或“Ortung und Navigation”（位置和導(dǎo)航），將在下面作為PNS被討論。在圖2中，一個(gè)典型的農(nóng)業(yè)網(wǎng)絡(luò)的簡(jiǎn)化方案展示了一個(gè)拖拉機(jī)-噴霧器的組合。這個(gè)圖表包括物理BUS線路，即骨干網(wǎng)絡(luò)。在這個(gè)BUS上，參與單元如拖拉機(jī)的電子控制單元(ECUs)、霧化器被連接協(xié)作起來。另外，兩項(xiàng)LBS服務(wù)也被連接到BUS上。一項(xiàng)服務(wù)代表LBS用戶站。另外一項(xiàng)是位置和導(dǎo)航服務(wù)，即位置數(shù)據(jù)的測(cè)量和處理系統(tǒng)。 2.4 分布式和中央數(shù)據(jù)處理的比較 一個(gè)分布式數(shù)據(jù)處理，農(nóng)業(yè)BUS，根據(jù)DIN 9684 或者ISO 11783， 定義了在測(cè)量系統(tǒng)和任何參賽者之間必要的數(shù)據(jù)交換；獨(dú)自地，任何一個(gè)ECU。每一個(gè)ECU怎樣得到計(jì)算機(jī)位置數(shù)據(jù)計(jì)算必要的幾何和運(yùn)動(dòng)參數(shù)的問題保持開放。每一個(gè)ECU知道從各自的結(jié)合點(diǎn)到目標(biāo)點(diǎn)的參數(shù)，但它不知道從結(jié)合點(diǎn)到測(cè)量點(diǎn)的參數(shù)。這些參數(shù)必須由其他ECU提供。沒有標(biāo)準(zhǔn)定義相應(yīng)的數(shù)據(jù)對(duì)象或請(qǐng)求數(shù)據(jù)的程序。對(duì)于分布式數(shù)據(jù)處理，這些定義必須補(bǔ)充。 另外,對(duì)于中央數(shù)據(jù)處理，一定要知道測(cè)量點(diǎn)和目標(biāo)點(diǎn)之間所有的運(yùn)動(dòng)參數(shù)。此外，方法必需被定義以便使用中央服務(wù)計(jì)算目標(biāo)點(diǎn)的位置數(shù)據(jù)。一個(gè)位置和導(dǎo)航服務(wù)需要擴(kuò)展標(biāo)準(zhǔn)，但以下的優(yōu)點(diǎn)在實(shí)際使用中是至關(guān)重要的。 ● 為了確定目標(biāo)點(diǎn)的位置數(shù)據(jù),相應(yīng)的控制單元(ECU)只有一個(gè)對(duì)話伙伴網(wǎng)絡(luò)。它獨(dú)立工作于各自的網(wǎng)絡(luò)配置，僅僅發(fā)送自己的參數(shù)和只接受它特定位置數(shù)據(jù)。 ● PNS從所有的ECU上接受參數(shù)。它知道所有一切幾何條件和車輛-工具組合的運(yùn)動(dòng)參數(shù)。因此，任何目標(biāo)點(diǎn)位置的確定是可能的。 ● 這個(gè)標(biāo)準(zhǔn)的定義了計(jì)算程序和明確的提出了目標(biāo)點(diǎn)的位置數(shù)據(jù)。 ● 計(jì)算位置數(shù)據(jù)的計(jì)算性能完全由PNS提供。沒有計(jì)算能力需要用于這個(gè)目的。 在前一節(jié)提到，提供位置和導(dǎo)航數(shù)據(jù)的服務(wù)已經(jīng)在LBS的計(jì)劃中。在下文中，將提到PNS的一個(gè)試?yán)鉀Q方案。 3.一項(xiàng)定位和導(dǎo)航服務(wù)的提議 此時(shí)，應(yīng)當(dāng)指出，下面的PNS的介紹是一項(xiàng)建議。它提供了一個(gè)平臺(tái)進(jìn)行討論，這可能導(dǎo)致這個(gè)服務(wù)標(biāo)準(zhǔn)化。 3.1 PNS的主要特征 PNS的特征首先依賴于它的使用目的。從前面所講的，很明顯的是，測(cè)量的位置數(shù)據(jù)在一個(gè)地點(diǎn)，用在不同的地點(diǎn)。為了提供需要的數(shù)據(jù)來指導(dǎo)車輛，控制工具的位置和協(xié)助任何一種精耕農(nóng)業(yè)，下面的條件必須滿足： PNS提供有關(guān)測(cè)量點(diǎn)的數(shù)據(jù)。 PNS提供有關(guān)參考點(diǎn)的數(shù)據(jù)。 PNS提供有關(guān)目標(biāo)點(diǎn)的數(shù)據(jù)。 這項(xiàng)服務(wù)的特點(diǎn)如下： 1.數(shù)據(jù)的請(qǐng)求和傳播的方式已經(jīng)標(biāo)準(zhǔn)化，數(shù)據(jù)被LBS (DIN 9684)定義和將被ISO 11783標(biāo)準(zhǔn)化。因此，它將不會(huì)在此討論。在下面,LBS將作為一種標(biāo)準(zhǔn)化的農(nóng)業(yè)BUS系統(tǒng)被使用。 2.數(shù)據(jù)的容量、準(zhǔn)確性、頻率和范圍是由數(shù)據(jù)的目的決定的。 3.滿足這些要求的硬件和軟件不應(yīng)被規(guī)范,應(yīng)該取決于生產(chǎn)廠家。 3.2關(guān)于位置數(shù)據(jù)測(cè)量和計(jì)算方法標(biāo)準(zhǔn)的影響 各種測(cè)量系統(tǒng)和PNS中用于決定位置數(shù)據(jù)的方法不再標(biāo)準(zhǔn)的范圍之內(nèi)?；谛l(wèi)星,機(jī)器視覺、慣性導(dǎo)航、地磁或這些情況的組合可能被應(yīng)用。作為一種結(jié)果,生產(chǎn)企業(yè)可以決定如何產(chǎn)生位置數(shù)據(jù)，只要他滿足了規(guī)定的要求和準(zhǔn)確性。 3.3 PNS在農(nóng)業(yè)BUS系統(tǒng)中的整合 在LBS中整合定位和導(dǎo)航服務(wù)存在一些好處，因?yàn)樵S多特性已經(jīng)被定義。LBS已經(jīng)包括在PNS的選項(xiàng)作為試驗(yàn)的標(biāo)準(zhǔn)。它允許實(shí)現(xiàn)服務(wù)作為一個(gè)獨(dú)立的物理單位或者為另外一個(gè)物理單位的邏輯單位。BUS接口和BUS協(xié)議的物理性能(DIN 9684, part 2)已經(jīng)被標(biāo)準(zhǔn)定義。為L(zhǎng)BS中服務(wù)的集成，系統(tǒng)的功能的定義是果斷的(DIN 9684，part3)。他們?cè)贚BS中定義節(jié)點(diǎn)的性能。第三部分也給了LBS服務(wù)一般的定義。 一項(xiàng)LBS服務(wù)形成與LBS參與者點(diǎn)對(duì)點(diǎn)的連接。LBS參與者使用服務(wù)時(shí)不會(huì)被其它使用者影響，一個(gè)LBS參與者也不能影響其他參與者對(duì)服務(wù)的使用。所有進(jìn)一步PNS的定義還不規(guī)范。 3.4 PNS操作的一般模式 PNS設(shè)計(jì)應(yīng)用以下的基本假設(shè)： 1.每一個(gè)ECU的只知道它自己的參數(shù)，包括參考點(diǎn)、目標(biāo)點(diǎn)、結(jié)合點(diǎn)位置、車輛類型或軸距的坐標(biāo)和數(shù)量。 2.只有ECU根據(jù)工作條件可以定義必要的時(shí)間間隔,準(zhǔn)確度和位置數(shù)據(jù)的分辨。 3.每一個(gè)ECU的可以選擇不同的任意時(shí)刻的位置數(shù)據(jù)。 4.參數(shù)和計(jì)算和提供的位置數(shù)據(jù)的方法將會(huì)在田野機(jī)械開始運(yùn)作過程之前被定義。 5.PNS提供了一些程序?yàn)閷?shí)施標(biāo)準(zhǔn)和車輛類型計(jì)算位置數(shù)據(jù)。 6.位置數(shù)據(jù)自動(dòng)（周期性）地或根據(jù)需求被提供。 為了滿足這些要求,服務(wù)窗口提供適當(dāng)?shù)墓ぞ?，同時(shí) ECUs 決定如何使用及使用哪個(gè)工具。這意味這它們定義一個(gè)或者多個(gè)任務(wù)。這樣一項(xiàng)任務(wù)基本上代表了一個(gè)命令表，包括激活具體工具使用的命令。這些任務(wù)被送到PNS，隨后PNS執(zhí)行這些任務(wù)。一個(gè)ECU的不同的任務(wù)相互獨(dú)立的被執(zhí)行。 圖3闡明了PNS與一個(gè)ECU之間的數(shù)據(jù)傳遞。同時(shí)，也顯示了PNS的主要部分。PNS的這些工具包括位置測(cè)量系統(tǒng)和測(cè)量點(diǎn)的數(shù)據(jù)，以及一系列處理這些數(shù)據(jù)的程序方法。程序如下： 1. 計(jì)算位置數(shù)據(jù)(位置程序)； 2. 計(jì)算位置數(shù)據(jù)值的平均值,最大值、最小值和積分的方法(算術(shù)程序)； 3. 輸入和輸出數(shù)據(jù)(傳輸程序)； 4. 傳遞數(shù)據(jù)到ECU（傳遞程序）； 5. 控制數(shù)據(jù)處理（數(shù)據(jù)控制程序）； 為了這些方法的執(zhí)行，ECU必須定義相應(yīng)的參數(shù)。它同時(shí)也定義位置數(shù)據(jù)的數(shù)據(jù)對(duì)象。 PNS的主要工具是一項(xiàng)執(zhí)行ECU定義的任務(wù)的程序系統(tǒng)。簡(jiǎn)而言之，程序系統(tǒng)解釋任務(wù)指令，調(diào)動(dòng)相應(yīng)的方法，計(jì)算要求的位置以及把數(shù)據(jù)送到ECU（電子控制單元）。 為了一項(xiàng)任務(wù)的定義，ECU生成一個(gè)任務(wù)庫(kù)。一個(gè)務(wù)庫(kù)主要是一系列調(diào)動(dòng)PNS的程序法或者調(diào)動(dòng)內(nèi)嵌的任務(wù)庫(kù)的指令。各種參數(shù)被定義并且放置在參數(shù)庫(kù)里。為了存儲(chǔ)被計(jì)算的位置數(shù)據(jù)，ECU必需定義數(shù)據(jù)庫(kù)。數(shù)據(jù)庫(kù)必需在激發(fā)相應(yīng)任務(wù)程序之前通過BUS從ECU傳送到達(dá)PNS。 3.5 PNS預(yù)定義的程序 PNS預(yù)定義的程序是一些處理位置數(shù)據(jù)或者控制數(shù)據(jù)處理的程序。不同的程序執(zhí)行不同的功能。不同的程序被一些獨(dú)特的標(biāo)識(shí)符區(qū)別。這些程序被稱為“內(nèi)部任務(wù)”（任務(wù)庫(kù)）。他將會(huì)成為標(biāo)準(zhǔn)的一部分用來定義標(biāo)識(shí)符，功能規(guī)格和調(diào)用程序規(guī)格。 3.5.1 位置程序 位置程序（計(jì)算位置數(shù)據(jù)的程序）是計(jì)算目標(biāo)點(diǎn)位置數(shù)據(jù)的數(shù)據(jù)。這些方法計(jì)算從最初的位置(輸入位置數(shù)據(jù)、資料的參考點(diǎn)的數(shù)據(jù)或以前計(jì)算的數(shù)據(jù)）到一種新的點(diǎn)的位置(輸出的位置數(shù)據(jù)、數(shù)據(jù)的目標(biāo)點(diǎn)或作為中間結(jié)果)。位置程序能夠滿足不同結(jié)構(gòu)位置的計(jì)算（考慮一、二或三維模型，嚴(yán)格耦合點(diǎn)，幾個(gè)基本類型車輛的不嚴(yán)格耦合點(diǎn)，工具和車輛-工具的結(jié)合）。這些程序從有關(guān)ECU執(zhí)行定義的參數(shù)庫(kù)得到他們的實(shí)際參數(shù)(目標(biāo)點(diǎn)的坐標(biāo),車輛的長(zhǎng)度、寬度、高度、類型或軸距)這是確定的有關(guān)實(shí)施ECU的。 圖4顯示了使用一個(gè)位置程序的一段任務(wù)庫(kù)。PNS的程序系統(tǒng)執(zhí)行這個(gè)程序庫(kù)。在任務(wù)庫(kù)的某一點(diǎn)上，它發(fā)現(xiàn)調(diào)用位置程序的指令。這個(gè)調(diào)用指令包括特定程序的標(biāo)識(shí)符和有關(guān)參數(shù)庫(kù)的引用。這時(shí)，程序系統(tǒng)擁有由以上的操作產(chǎn)生的實(shí)際位置數(shù)據(jù)。現(xiàn)在它使用這些實(shí)際數(shù)據(jù)作為輸入數(shù)據(jù),和引用參數(shù)庫(kù)用于位置程序。然后，它執(zhí)行特定的程序。該程序使用指定的參數(shù)計(jì)算輸出的位置數(shù)據(jù)。然后，它返回到程序系統(tǒng)。位置程序的輸出數(shù)據(jù)成為新的實(shí)際位置數(shù)據(jù)。程序系統(tǒng)繼續(xù)執(zhí)行下面的指令。 3.5.2 算術(shù)程序 算術(shù)方法被用來計(jì)算位置數(shù)據(jù)的平均值,最大值、最小值或者積分值。一個(gè)算術(shù)程序從程序系統(tǒng)的實(shí)際位置數(shù)據(jù)或從特定數(shù)據(jù)庫(kù)得到位置輸入數(shù)據(jù)。它使用在調(diào)用指令里決定的參數(shù)庫(kù)中的參數(shù)計(jì)算輸出位置數(shù)據(jù)。然后，計(jì)算結(jié)果數(shù)據(jù)被存儲(chǔ)在一個(gè)被定義的數(shù)據(jù)庫(kù)里。 圖5展示了一個(gè)算術(shù)程序使用的例子。在任務(wù)庫(kù)的某一點(diǎn)上，它發(fā)現(xiàn)調(diào)用算術(shù)程序的指令。這個(gè)調(diào)用包括具體程序的標(biāo)識(shí)符,一個(gè)有關(guān)參數(shù)庫(kù)的引用,一個(gè)目的數(shù)據(jù)庫(kù)的引用和源數(shù)據(jù)庫(kù)選擇性的引用。這個(gè)程序系統(tǒng)采用實(shí)際數(shù)據(jù)和參考數(shù)據(jù)用于程序計(jì)算。根據(jù)調(diào)用規(guī)格,算術(shù)程序從程序系統(tǒng)(沒有定義的數(shù)據(jù)庫(kù)參考)或一種數(shù)據(jù)資源(數(shù)據(jù)資源I)得到輸入數(shù)據(jù)。它計(jì)算被要求的值并把計(jì)算結(jié)果存儲(chǔ)在一個(gè)數(shù)據(jù)庫(kù)里（數(shù)據(jù)庫(kù)II）。計(jì)算參數(shù)是從定義的參數(shù)庫(kù)中得到的。程序發(fā)揮到程序系統(tǒng)并繼續(xù)執(zhí)行。實(shí)際的位置數(shù)據(jù)沒有被改變。 3.5.3 傳輸程序 PNS定義了三種類型的傳輸程序。輸入程序是用來裝載作為實(shí)際位置數(shù)據(jù)的確定的數(shù)據(jù)庫(kù)位置數(shù)據(jù)到PNS的程序系統(tǒng)。輸出程序存儲(chǔ)實(shí)際位置數(shù)據(jù)到一個(gè)在調(diào)用指令里預(yù)先定義了的數(shù)據(jù)庫(kù)。輸入/輸出程序被用來從一個(gè)源數(shù)據(jù)庫(kù)到目的數(shù)據(jù)庫(kù)之間傳輸數(shù)據(jù)。 圖6顯示了一個(gè)使用輸入和輸出程序的例子。輸入程序的調(diào)用指令包括具體程序的標(biāo)識(shí)符和源數(shù)據(jù)庫(kù)的引用。在執(zhí)行輸入程序之前，程序系統(tǒng)為程序提供源數(shù)據(jù)庫(kù)的引用。然后，程序執(zhí)行和得到位置數(shù)據(jù)，并將它作為實(shí)際位置數(shù)據(jù)返回給程序系統(tǒng)。以前的實(shí)際位置數(shù)據(jù)被損壞。系統(tǒng)繼續(xù)進(jìn)行。對(duì)于輸出程序的使用，實(shí)際位置數(shù)據(jù)與目的位置數(shù)據(jù)庫(kù)提供參考。輸出程序?qū)?shí)際數(shù)據(jù)放到目的數(shù)據(jù)庫(kù)并返回到程序系統(tǒng)。實(shí)際位置數(shù)據(jù)仍然有效。 3.5.4 傳遞程序 傳遞程序發(fā)送具體的位置數(shù)據(jù)到ECU。源數(shù)據(jù)在調(diào)用指令(或一個(gè)數(shù)據(jù)庫(kù)或程序系統(tǒng)的實(shí)際數(shù)據(jù))里被定義。當(dāng)執(zhí)行一個(gè)傳遞程序時(shí)，它得到具體的位置數(shù)據(jù)并傳送到ECU。 3.5.5 數(shù)據(jù)控制程序 數(shù)據(jù)控制程序控制一個(gè)任務(wù)庫(kù)的執(zhí)行。程序流程是控制時(shí)間或距離。PNS的程序系統(tǒng)調(diào)查任務(wù)庫(kù)。假如確定的時(shí)間間隔已過期或已超出距離限制，程序?qū)?zhí)行下列指令。否則，程序系統(tǒng)跳到數(shù)據(jù)庫(kù)的結(jié)尾。 Computers and Electronics in Agriculture 25 (2000) 87–106 Providing measured position data for agricultural machinery Hermann Speckmann Federal Agricultural Research Centre Braunschweig (FAL), Institute for Biosystems Engineering, Bundesallee 50, D-38116 Braunschweig, Germany Abstract Agricultural machinery and vehicles require position data for guidance and to control implements for optimal working positions. Position data are also needed for such applica- tions as precision farming. The necessary accuracy, resolution and frequency of position data vary according to the specific application. Only one system, installed at a central vehicle (e.g. the tractor), should provide position data for each task. The basic concept for the proposed central system is that position data are calculated in accordance with the application and transferred directly to the point at which they will be used. The paper describes the fundamentals of measurement and calculation of position data, and gives a short introduc- tion to the existing agricultural networks to transfer these data. It concentrates on a proposal for a network service to provide and transfer position data. The solution discussed is based on the agricultural BUS (DIN 9684, ISO 11783). ? 2000 Elsevier Science B.V. All rights reserved. Keywords: Local area network; Controller area network; Agricultural BUS system; LBS; Calculation of position; Calculation of direction; LBS service :locate:compag 1. Introduction The purpose of position guidance is to bring the means of production to the plants, which grow at a fixed location on the field. The plants, or rather their location on the field surface, are the reference for guidance. Position data are needed to guide agricultural vehicles, to control implements and to support precision farming. Accuracy, resolution and frequency depend on their application. E-mail address: hermann.speckmann@fal.de (H. Speckmann) 0168-1699:00:$ - see front matter ? 2000 Elsevier Science B.V. All rights reserved. PII: S0168-1699(99)00057-5 H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–10688 It must be emphasized that this paper does not address the problem of suitable sensors to generate the data. Rather, the problem studied here is that a position signal is generated with reference to a certain location on the mobile unit, but this position is not identical with the location where the position data are needed. Moreover, position information may be needed for several purposes at the same time, and the configuration of the vehicle–implement combination may change frequently. As mentioned by Freyberger and Jahns (1999), Wilson (1999), the measuring system can either be an absolute position system, such as the satellite system described by Bell (1999), or a relative system, such as the machine vision systems described by Debain et al. (1999), Hague et al. (1999). It may also include auxiliary sensors. Sensor systems measure position only in reference to a specific location, such as the mounting point of the camera or the foot of the aerial. In the following presentation, this location is called the measuring point. For various reasons, the location of this measuring point is predetermined, meaning the satellite antenna will be mounted as high as possible on the roof of the tractor cab to minimize shading. A camera will be mounted where optimal view is guaranteed. Movement caused by rough or sloping field surfaces may cause the measured position and the position on the field surface to differ widely. For example, for a vehicle with a satellite antenna mounted on top of the cab, at about 3.5 m, driving on a sloping surface of 10°, the difference in direction of the inclination will be about 60 cm. Fig. 1 illustrates this scenario for one dimension. In this example, it may be appropriate to calculate the position of a reference point. Bell (1999) proposes the middle rear axes of the Fig. 1. Difference in position for two locations due to sloping terrain. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–106 89 tractor as a reference point. A point in the field surface, for example, vertical under the middle of the rear axis seems more appropriate for some applications. For certain applications, such as the control of implements, the position of a certain point of the implement may be of final importance. This point will be called the target point. In cases where position data are needed for different purposes, it is not very efficient to measure the position for each purpose separately with an independent measuring system. Multiple hardware can be avoided when the position is measured only once, and the positions of the other points on the vehicle or implements are calculated. This is possible if position and attitude are measured, and the spatial vector between the measuring point and the point to be calculated is known. If both points are rigidly coupled, meaning that both points are on the tractor, the vector between these points is constant, and a simple matrix calculation yields the result. If these points are not rigidly coupled, meaning, for example, that one point is on the tractor and the other is on an attached implement, the vector is variable. Additional measurements become necessary to establish the vector between these two points or other principles to calculate the position of the target point must be applied. 2. Data processing and data transfer Position data of any point on the vehicle or implement can be calculated from the position and attitude measured at a measuring point. This calculation can be made by the measuring system (central data processing) or by each system requesting target position data (distributed data processing). 2.1. Distributed data processing The measuring system serves only as an intelligent sensor in the case of distributed data. It measures position and attitude on request, and provides these data without any processing. Characteristics such as frequency and accuracy are determined by the requesting unit. This unit performs all processing to calculate the position. The unit must know the position of the measuring point and all relevant parameters to do this. The advantage of this procedure is that the measuring device can be relatively simple. On the other hand, each requesting unit needs the full capacity to perform this calculation. 2.2. Central data processing The measuring unit is extended by components to calculate the position of target points for any user. This measuring and processing system forms one unit of a so-called position and navigation service (PNS), which provides final position data of any target point. In this case, only one measuring and processing system is necessary even when position data are requested by more than one user. To do so, only the PNS must know all of the relevant parameters for the calculation. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–10690 2.3. Data transfer A data transfer is necessary no matter where the data are processed. For such a data transfer, a standardized network is appropriate. For agricultural purposes, a BUS for data transfer between mobile units and stationary farm computers exists. The agricultural BUS system (LBS) has been standardized to exchange information between the electronic units (LBS participants or BUS nodes) in a network. The standard defines the physical layer of the network, network protocol, system management, data objects and central services for common tasks (Speckmann and Jahns, 1999). The LBS has been standardized as DIN 9684 (DIN, 1989–1998). Currently, efforts are being made to establish an international standard (Nienhaus, 1993), ISO 11783, for such purposes. Like LBS, ISO 11783 will also define an agri- cultural BUS as an open system to exchange data on agricultural machinery, particularly on tractor–implement combinations and from the mobile units to the stationary farm computer. The standards are based on the controller area network data protocol (CAN; BOSCH, 1991). Corresponding hardware is on the market. In the LBS, data objects are defined for the transmission of general position data (geographical positions: longitude, latitude, altitude, or position in a tramline). The standard allows definition of additional data objects such as multidimensional distances, directions and speeds. No data objects exist presently in the LBS for geometric implement parameters. ISO 11783 provides, in Part 7 (Implement Mes- sages Application Layer), the first definitions of implement navigational offsets. Current standards do not define where which data are processed. Therefore, it is immaterial on which unit the BUS calculates the data for the target point, and which unit or units measure the data. The LBS provides so-called LBS services to execute common tasks. LBS services are functional units, which perform frequently recurring tasks for LBS participants. Such a service is the LBS user station. This is a central interface to the user (operator) for input and output of data which is at the disposal of any node (LBS participant) on the BUS. Another service provides the data exchange between the mobile unit and the stationary computer, the farm computer. Some more services are named in the LBS but not yet stan- dardized in detail, such as for diagnosis services or the service ‘Ortung und Navigation’ (position and navigation), which will be discussed in the following as PNS. In Fig. 2, an exemplary simplified scheme of an agricultural network is shown for a tractor–sprayer combination. This scheme includes the physical BUS line, which is the backbone of the network. At this BUS, participants such as electronic control units (ECUs) of the tractor and sprayer are coupled. Additionally, two LBS services are connected on the BUS. One of these services represents the LBS user station. The other is the LBS service ‘position and navigation’, with the measuring and processing system for position data. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–106 91 Fig. 2. Scheme of an agricultural network in a tractor–sprayer combination. 2.4. Comparison of distributed and central data processing For a distributed data processing, the agricultural BUS, according to DIN 9684 or ISO 11783, defines the necessary data exchange between the measuring system and any participant; respectively, any ECU. The question how each ECU gets geometric and kinematic parameters that are necessary to compute position data remains open. Each ECU knows its own parameter from its coupling point to the target point, but it does not know the parameter from the coupling point to the measuring point. These parameters must be provided from other ECUs. None of the standards define corresponding data objects or procedures requesting the data. For distributed data processing, these definitions have to be supplemented. Also, for central data processing, all kinematic parameters between the measur- ing point and the target point must be known. In addition, methods are to be defined for the use of the central service with regard to the calculation of position data of target points. A position and navigation service requires an extension of the standards, but the following advantages in practical use are essential: To determine the position data of a target point, the corresponding ECU has only one dialogue partner in the network. It works independently from the respective network configuration, delivers only its own parameters and receives only its specific position data. The PNS receives parameters from all ECUs. It knows all geometric conditions and kinematic parameters of the vehicle–implement combination. Thereby, an unambiguous determination of the position of any target point is possible. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–10692 The standard defines the procedures to calculate and present the position data of a target point unambiguously. The computing performance to calculate the position data is provided solely by the PNS. No computing capacity is needed for this purpose from the ECUs. As mentioned in the previous section, a service to provide position and naviga- tion data is already planned in the LBS. In the following, a sample solution of a PNS is presented. 3. Proposal for a positioning and navigation service At this time, it should be mentioned that the following description of a PNS is a proposal. It provides a platform for discussion, which may lead to the standard- ization of such a service. 3.1. Main features of a PNS The features of a PNS depend, first of all, on the purpose for which it will be used. From the foregoing, it is clear that position data are measured at one location and used at different locations. The following requirements must be fulfilled to provide the data needed to guide a vehicle, to control positions of implements and to assist any kind of precision farming: The PNS provides data related to the measurement point(s). The PNS provides data related to the reference point(s). The PNS provides data related to the target point(s). The characteristics of such a service are as follows: 1. The way the data are requested and transmitted is already standardized and defined by the LBS (DIN 9684) and will be standardized by ISO 11783. Therefore, it will not be discussed here. In the following, LBS will be used as a standardized agricultural BUS system. 2. The volume, accuracy, frequency and range of the data are determined by the purpose of the data. 3. The hardware and software to fulfil these demands should not be standardized, but be determined by the manufacturers. 3.2. Influence of the standard on measuring and calculation methods for position data The kinds of measuring systems and methods used to determine position data by the PNS is not in the scope of the standard. Systems based on satellites, machine vision, inertial navigation, geomagnetics or a combination of these may be applied. As a consequence, the manufacturer may determine how to generate the position data as long as he meets the stated requirements and accuracy. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–106 93 3.3. Integration of the PNS into an agricultural BUS system There are some benefits of integrating the positioning and navigation service into the LBS, because many characteristics are already defined. The LBS already includes the option of a PNS as part of the standard. It allows the realization of a service either as an independent physical unit or as a logical unit inside of another physical unit. The physical properties of the BUS interface and the BUS protocol (DIN 9684, part 2) are defined by the standard. For integration of the service into the LBS, the definitions of the system functions are decisive (DIN 9684, part 3). They define the performance of the nodes at the LBS. Part 3 also gives the general definitions of LBS services. An LBS service forms a point-to-point link with LBS participants. The use of a service by an LBS participant can neither be influenced by other users, nor can an LBS participant influence links between the service and other participants. All further definitions of the PNS are not yet standardized. 3.4. General mode of operation of the PNS For the design of the PNS, the following basic assumptions apply: 1. Each ECU knows only its parameters, meaning coordinates and numbers of reference points, target points, positions of couplings, vehicle types or wheelbases. 2. Only the ECU can define necessary time intervals, accuracy and resolution for position data, depending on the working conditions. 3. Each ECU can get different position data at arbitrary times. 4. Parameters and the way of calculating and providing position data will be defined before the working processes of the field machinery are started. 5. The PNS provides a library of procedures to calculate position data for standard implement and vehicle types. 6. Position data are provided automatically (cyclically) or on demand. To meet these requirements, the service provides the tools, and the ECUs determine how and which tools are used. This means they define one or several task(s). Such a task basically represents a list that includes commands to activate the specific tools. These tasks are sent to the PNS, which subsequently performs these tasks. Different tasks of one ECU are executed independently of each other. Fig. 3 illustrates the data transfer between the PNS and one ECU. It also shows the main parts of the PNS. The tools of the PNS include the system for measuring the position and attitude data of the measuring point, and a library of methods to process these data. Methods exist: to calculate position data (position methods); to calculate mean, maximum, minimum and integral values of position data (arithmetic methods); to export and import data (transport methods); to send data to the ECU (transmission methods); and to control the data processing (data control methods). H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–10694 For some of these methods, the ECU has to define corresponding parameters. It also defines data objects for position data. The central tool of the PNS is the program system to execute the tasks defined by the ECU. Simplified, the program system interprets the instructions of the task, calls the corresponding methods, calculates the demanded position and sends the data to the ECU. For the definition of a task, the ECU generates a task resource. A task resource is mainly a list of instructions to call methods of the PNS or to call nested task resources. Parameters are defined by the ECU and placed in parameter resources. To store calculated position data, the ECU has to define data resources. The resources have to be transmitted from the ECU via the BUS to the PNS before activating corresponding tasks. Fig. 3. Strcture of a PNS and its data exchange with one ECU. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87–106 95 Fig. 4. Example of the use of a position method in the course of a task resource. 3.5. Predefined methods of the PNS Predefined methods of the PNS are procedures to process position data or to control this data processing. Methods exist to perform different functions. The different methods are distinguished by a unique designator. They are called ‘within tasks’ (task resources). It will be a part of the standard to define the designators, function specifications and calling specifications of the methods. 3.5.1. Position methods Position methods (methods to calculate position data) are the basis for calculat- ing position data of target points. These methods calculate from an initial position (input position data, data of a reference point or previously computed data) the position of a new point (output position data, data of a target point or as an interim result). Position methods exist for different configurations (one-, two- or three-dimensional model considerations, rigidly coupled points, non-rigidly coupled points for several basic types of vehicles, implements and vehicle–implement combinations). These methods get their actual parameters (coordinates of the target point, vehicle length, width, height, type or wheelbases) from parameter resources which are defined by the concerned implement ECU. Fig. 4 shows a section of a task resource using a position method. The program system of the PNS executes this task resource. At a certain part of the task resource, it finds a calling instruction for a position method. This calling instruction includes the designator of the specific method and a reference to a relevant parameter resource. At this moment, the program system owns actual position data, which result from previous operations. Now it uses these actual data as input data, and the parameter resource reference for the position method. Then, it executes the specified me