【正文】 rol point for a coverage. Tics allow coverage coordinates to be registered to a mon coordinate system (., UTM meters, State Plane Feet, etc.) and, therefore, relate locations of features in a coverage to locations on the Earth’s surface. Tics are very important for registering map sheets during digitizing and editing. TIC 點(diǎn) 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 All tic information for a coverage is stored in the TIC file which contains the following items: IDTIC The UserID for each tic. XTIC The tic’s xcoordinate. YTIC The tic’s ycoordinate. 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 LABLE 點(diǎn) 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 Nodes indicate the endpoints and intersections of arcs. They do not exist as independant features. That is, they cannot be added or deleted except by adding and deleting arcs. Nodes can, however, be used to represent point features which connect segments of a linear feature (., intersections connecting street segments, valves connecting pipe segments). NODE 點(diǎn) 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 NODE 點(diǎn)的類型 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 NODE 點(diǎn)的存儲(chǔ) When nodes are used to represent point features, descriptive data is stored in a node attribute table (NAT). There is one record in the NAT for each node. The record is related to the node by the node抯 internal sequence number. At a minimum, the following items are contained in a NAT: ARC Internal sequence number of one of the arcs that connects at the node location. cover Internal sequence number of the node. coverID Userassigned feature ID. When an NAT is initially created, node IDs are automatically set equal to the node’s internal sequence number. 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 A node is an endpoint of an arc. The fromnode is the first vertex in the arc。 set to 0 if the coverage does not contain polygons. RPOLY Internal sequence number of the right polygon。s origin /* false easting (meters) /* false northing (meters) 投影文件 PRJ 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 4) Coverage 的屬性特征 Feature class Feature attribute table INFO database Feature attribute table coverage directory Point cover.PAT Arc cover.AAT Node cover.NAT Route cover.RATroute route.rat Section cover.SECsection route.sec Polygon cover.PAT Region cover.PATregion region.pat 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 5) Coverage 的存儲(chǔ)方法 Coverage 是一個(gè)目錄，其中的重要文件： ? ? ? ? ? PRJ ? ARC ? 以中國(guó)省界圖為例顯示文件 ? 詳細(xì)文件類型件 (Coverage Data Model ) 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 6）、 Coverage 的重要容限值 ? 模糊容差（ Fuzzy tolerance） ? 啞弧段長(zhǎng)度（ Dangle tolerance） ? 結(jié)點(diǎn)閉合容差 (Node match tolerance) ? 拐點(diǎn)容差 (Weed tolerance) ? RMS誤差 ? TOL文件 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 模糊容差（ Fuzzy tolerance） Coverage resolution is influenced by the fuzzy tolerance, which represents the minimum distance separating all arc coordinates (nodes and vertices) in a coverage. By definition, it also defines the distance a coordinate can move during certain operations. The fuzzy tolerance is an extremely small distance used to resolve inexact intersection locations due to limited arithmetic precision of puters. Fuzzy tolerance values typically range from 1/10,000 to 1/1,000,000 times the width of the coverage extent defined in the coverage BND file. 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 北京師范大學(xué)資源科學(xué)研究所 /科學(xué)技術(shù)處 2022年度研究生課程：地理信息系統(tǒng)理論方法與應(yīng)用 啞弧段長(zhǎng)度（ Dangle tolerance） A dangling arc has the same polygon on its left and right sides (as defined by the polygon internal number) and at least one dangling node. The dangle length defines the minimum allowed length for a dangling arc in a coverage. The C