Basic concept of geometric network
Mobile population, transportation and distribution of goods, and services, resource and energy transmission, information exchange occurs within a definable geometric network system. In ArcInfo8, the network is defined as a one-dimensional non-planar image consisting of elements, or geometric networks. These elements are limited to the geometric network, so it is also considered to be a network element. Topological relationship between ArcInfo8 automatically maintains network elements in a geometric network. Network connectivity is built on geometric and uniformity, which is the origin of the geometric network name. For the rules of connectivity, see Establishing Geometric Network Rules.
A geometric network has a corresponding logical network. The element geometry of the geometry network truly constitutes the network, and the logical network is a physical representation of network connectivity. Each element in the logical network is associated with geometric elements in the geometry network.
Once there is a geometric network, ArcMap, and ArcCatalog have tools that deal with network elements. For example, editing and tracking on the web, and the feature class in the management network is automatically completed by the ArcGIS system. For specific methods for how to build geometric networks and build, see geometric networks.
Network element type
Geometric networks include edge elements and intersections of the network. One instance of side elements is a water pipe, and the intersection element is its valve. The side and edges must be connected by intersection. Edge elements in the side elements and logical networks, intersection elements in the intersection element, and logical networks.
There are mainly two types of network elements, simple and complex. Simple network elements correspond to a single network element in the logical network. Complex network elements correspond to multiple network elements in the logical network.
Simple side elements correspond to separate edge elements in the logical network. Simple side is usually only connected to two intersection elements, one at one end there. If a new intersection feature is captured in the middle of a simple element (thus establishing connectivity), the simple side feature will be physically divided into two new features.
Composite edges correspond to one or more edge elements in the logical network. The composite edge is not only two intersections at its endpoint, but also add additional intersection points in the middle. If a new intersection feature is captured on a composite edge feature, this composite edge will remain inconvenient, still a feature. The capture intersection allows the composite edge logic to be split, for example, before it is connected to a side element before it is connected, and now it corresponds to two edge elements.
A composite intersection is an independent element that corresponds to any number of edges and intersection elements in the logical network. For example, the pump in the water supply network can be a composite intersection. Although the pump element is stored as a composite intersection element in the geographic database, it can include a set of water pipes, pump instruments and valves in the logical network, which affect the flow of water in the water pump station. The combination of these devices can be expressed as a collection of seven intersection elements and six side elements.
In the following example, the pump station is a single surface entity in the geometry network, but it includes a combination of water pipes, valves, instruments, and electric pumps in the logical network. So it is a composite intersection element.
Figure 1. Geometric network
Composite intersections can only be implemented by custom elements. To learn more, please refer to Explore ArcObjects.
Source and endpoint
The network is often used to simulate the real world system, and the direction of movement in these systems is well defined. For example, the flow direction of the electric grid is from the power station to the user. In the tap water network, the flow direction of the water may be as good as it is defined in the grid, but the overall direction of the water flow is from the water station to the user or from the user to the sewage treatment.
The flow direction in the network is calculated from a set of origins and endpoints. In the above example, the flow of electricity and water is driven by the source and end points. The fluid leaves the source, such as electricity station and water station, flowing to the end point, such as water treatment (in the case of wastewater network).
The intersection feature in the geometry network can be used as the source and end points. When you have established a new intersection element in the network, you can specify whether this feature can represent the source, focus or anything in the network. If you specify which feature can be or end, a "ancillaryrole" is added to this feature set, which is used to record this feature is a source, the end, or nothing. When you calculate the flow direction for the geometric network in ArcMap, the flow direction is calculated based on these source and endpoints. For example, you can use a bucket in your water network to store water, so it will be (temporary) to change from the source to no (NONE) in the network. The flow direction of the network will be affected by the system from new computing, and any tracking on the network will affect the change in the flow direction of the bucket state. For more information on network tracking, please refer to the network tracking.
Weight of the network
The network can have a set of weights associated with it, and the weight can be used to represent the consumption of one element travel in the logical network. For example, in the water grid, a certain pressure is lost due to the friction of the inner wall of the tube in the pipe in the pipe.
The weight is calculated by several elements. In the example of the transportation conduit above, the factors affecting the weight should be the length of the tube.
A network can associate any number of weights. The elements of the network can have several, all or no weights related to its properties. The weight of each element is determined. One weight can be associated with a property of a element, but at the same time can be associated with multiple elements. For example, a weight called diameter can be associated with a diameter attribute of the water pipe, and can be associated with the diameter attribute of the branch of the water pipe.
Element of elements
Any side or intersection in the geometry network element can be "enabled or disabled" in the logical network. Close elements in the logical network are an obstacle. When the network is tracked, tracking will stop in a place where any obstacles or closing elements are encountered.
The enabled state of the network element has a field called "enable" to maintain. It has two values: true or false. This field is automatically added to the input feature class when the network is established from a simple feature class. ENALBLED is a must field when you use ArcCatalog to create a network element. For details, please refer to: Geodatabase Items. When adding new elements to the network, they are automatically set to "enabled". For more information on editing network elements, please refer to EDITING NETWORK FEATURES.
The weight, access value, and "enable" field stored in the network are the user's status view in the logical network. When analyzing networks, such as tracking and flow analysis, the values of these fields are not directly referred to, the "entlbed", an accessory value, or its weight. Instead, the state of these elements is stored in the logical network for operation as an operation. This is why it is for efficiency.
When editing network elements and changing the "Enabled", an accessory function, or weight field, the state of the element of the internal topology table is synchronized, so that the field value of the element is consistent.
Thoughts on the efficiency of implementation
Geometric network consists of a certain number of intersections and feature classes. When editing geometry in ArcMap, the topology relationship between the elements is automatically maintained. The advantage of doing this is that there is no need to come back to build a topology after editing. Of course, this also increases the necessary time necessary to maintain network communication relationships during editing.
The topology in the network is based on geometric consistency. If a intersection is added to one side, the connection between the edges and intersections will be established to establish a topological relationship. When adding a new feature in the network, geometric consistency must be discovered. Therefore, each element class in the network must analyze the consistency of this new element with the network by executing a spatial query. If consistency is discovered, network connectivity is established.
When the connectivity is discovered, you must perform an independent space query within the network on the server. When editing the network, if you use the editing buffer, these queries are not necessary to perform queries on the server, so the speed is very fast. If you use the editing buffer, you will not perform efficiency because of a large number of elements in the network. When performing elements increase and move existing elements, use the editing buffer to increase the execution efficiency to a considerable extent. For more information, please see Editing Network Features and Managing The Edit Cache. To minimize the number of features in the geometry network, you should set the feature class by using subtypes.
If your feature class strip is made by different properties, you can set different data sheets to manage different subclasses in a table, or you can put all properties in a table in a database. An unrelated property setting is set as space.
