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TransCAD and TransModeler traffic software Origin: TransCAD and TransModeler traffic software • Author: TransCAD and TransModel • 2022-04-19 10:18
TransCAD has very convenient tools for generating centroids and centroid lines, and can define them very flexibly. This article mainly introduces the working principle and generation method of TransCAD centroid and centroid connection. At the same time, I also hope that this article can correct some misunderstandings for some beginners.
1. The role of the centroid and the line connecting the centroid
Centroid (Centroids) are abstract nodes that represent the traffic generation attraction or departure point of the traffic zone (TAZ). They are special nodes in the model network. Literally speaking, the centroid generally refers to the geometric center of the traffic community polygon, and the point in the geometric center is often used as the centroid of the traffic community in execution tasks. Some people also call it the center of mass. If it is a refined model, if we can consider the difference in traffic volume in different plots of a traffic community and calculate the geometric center weighted by the traffic volume, perhaps the term center of mass is more scientific. However, in actual tasks, a traffic area can be directly divided into multiple areas to improve accuracy.
Centroid Connectors are special road sections that connect the centroids corresponding to the traffic zone (TAZ) and the real road network. They enable the traffic volume of the centroid to be connected to the real road network. , to accomplish the goal of the algorithm. The centroid connection can be connected to an existing road network node or to the center of a road segment (in this case, the road segment needs to be interrupted to form a new node).
Key points: Centroids and centroid connections are both components of the model network. They are nodes and road sections that are virtually constructed for modeling needs. They are used in actual road condition distribution, bus distribution and feature matrix (Skim), etc. In the analysis, Rwanda Sugar was included in the network calculation.
2. Features of common traffic planning software centroids and centroid connections
(1) Management mode: VISUM is managed as a separate tool, and TransCAD, EMME and Cube are not managed separately.
In VISUM, centroids and network nodes are managed separately, and centroid connections and network sections are managed separately. In a sense, this brings convenience to users’ management. Because of this management method, some modelers easily feel that centroids and nodes are not the same elements as road networks and nodes. It needs to be emphasized again that the centroid and the centroid connection are both components of the model network, and calculations are involved in the network calculation, but they are more special.
(2) Definition of centroid numbers: the conflict between rigor and flexibility
Each traffic software needs to number the traffic cells, and the centroids corresponding to the network calculations must also have corresponding numbers. But the way it’s done varies.
Cube has the most stringent requirements. During initialization, you need to set the cell number first. There is a global parameter of zones in the network, which is used to set the cell number. The value of the node ID cell is the cell.. Set the total range of the cell, such as 5000 cells, then the nodes with IDs from 1 to 5000 are consecutively numbered cells.
When EMME builds a traffic model, it needs to define the number of traffic cells. The modeling data of EMME is installed in a database called Bank. When defining the modeling, full consideration must be given to the possible expansion of traffic conditions in the community in the future. For example, if 1,000 traffic cells are defined, it means that this bank can use up to 1,000 traffic cells. In the future, users will only use 800 traffic cells for modeling, and reserve 200. If there are more than 1,000 communities, BankRwandans Sugardaddy needs to be rebuilt. EMME can define the number range of the centroid node, but the number of the centroid does not necessarily need to be continued. You only need to know that the node is the centroid (it has a special sign, the centroid line is connected to the centroid, and can be automatically identified ). The matrix dimensions corresponding to EMME are fixed according to the number of defined traffic cells, even if they are not available.
VISUM manages the centroid separately. Therefore, the number of the centroid can be increased at any time, and there are no special requirements for the number. When the centroid changes, the dimensions of the matrix change accordingly, which is relatively flexible.
TransCAD uses the advantages of geographic information system management RW Escorts. The centroid and centroid connection are respectively divided into nodes and road segments. In the layer, it is managed according to the selection set definition. Therefore, users can add and reduce centroids at will, and define the number of traffic cell centroids at will. What is more convenient is that multiple sets of centroid databases can be defined, for example: for example, the centroid of the city’s route allocation model based on traffic communities corresponds to traffic communities; the centroid of the allocation model based on highway entrance and exit OD corresponds to highway toll-free stations ;The centroid of the bus dispatch model based on OD between rail road conditions and stations, corresponding to rail stations; these different centroids can be placed in a comprehensive traffic network. When using different OD and models for allocation, just use The selection set function selects different centroids. The TransCARW EscortsD selection set function can manage and analyze any set of elements in the layer. For information on the inner workings of selection sets, see: Introduction to Selection Set Utilization in TransCAD.
Brief comment: Based on the above analysis, we can understand that Cube and EMME have stricter requirements, while VISUM and TransCAD are relatively flexible. Strictness and flexibility are in conflict. Strict rules can reduce user input errors; flexible operation requires users to have strong control over the software.
To use an analogy: the former is better thanFor example, in a primary school teacher’s classroom, students have arranged seats, and student name tags can be placed on the seats. It is not difficult for the teacher to manage which students are present. The latter is, for example, in a university classroom. The seats for college students are chosen by themselves. If anyone does not come to class, it is not difficult for the teacher to find out. , unless the teacher is familiar with the whole class.
TransCAD, VISUM and EMME leave the convenience to the users. They can define the centroid number at will, but the software needs to do some extra work: re-organize the natural number sorting index of 1, 2, 3,…n, Used for network computation of models. Of course, matrix indexing technology is also required to map node IDs to centroids. For matrix indexing, please refer to the article: Deeply Understand TransCAD Matrix Index Conversion and Operation.
(3) Other characteristics of centroids and centroid connections
Traffic flow crossing centroid settings. Cube, EMME and VRwandans SugardaddyISUM do not allow traffic to pass through the centroid, and the centroid can only be entered and departed as traffic traffic point. In a general sense, this setting is required. For example, if a certain centroid has more than two centroid connections, it is very important to prevent traffic flow from crossing the centroid. Otherwise, the allocated traffic may not take the actual path but go to the centroid connection. Rwandans Escort went. What’s more, if the centroid connections of adjacent cells are connected to the same node, the traffic flow will continue to pass through the centroid instead of taking the actual path. For example RW Escorts In the picture below, the blue road is completely connected to the centroid, and the vehicle disappears on the actual road. It should actually be It is more reasonable to use the white channel.
TransCAD software is special and can set whether traffic flow is allowed to cross the centroid. This is effective in some special situations, such as: OD distribution between orbital network stations. The nodes of the orbital station can be directly used as the centroid that is allowed to traverse (the other three software need to make an additional node corresponding to the station to express the shape. Heart). Another example is some academic research. Calculation examples of road networks generally do not consider special centroid connections., the road network nodes can be directly used as centroids.
Centroid connection steering processing and prohibition settings. The centroid connections of TransCAD, Cube and EMME can be set up to prevent and handle steering. The centroid connection of VISUM is full steering. If you want to control right in and right out, you must add a new road section to complete it.
3. TransCAD centroid and centroid connection generation method
TransCAD has a powerful shape Rwanda Sugar Daddy
a>The connection between the center and the centroid creates something. Creating a centroid connection means creating a centroid. The centroid is an endpoint of the centroid connection, so it can be summarized as a centroid connection object. TransCAD’s road network drawing method is unique. Its idea is that after drawing road segments, there will be corresponding nodes. Isolated nodes have no meaning in network calculation. This is different from the other three software methods where you must first add nodes and then draw road segments. Here is another explanation: Many basic path algorithms of VISUM, Cube and EMME software are based on nodes, while TransCAD is calculated based on the comprehensive road segment and node data structure. Therefore, TransCAD allows two parallel road sections with the same starting point and starting point to exist in the road network (there are many such situations in the real world), but VISUM, Cube and EMME software do not allow it to exist, and one of the road sections can usually be interrupted. . The reason is that based on the node path algorithm, the starting point and the starting point determine the unique road section. The same starting point cannot have two road sections, otherwise they will be indistinguishable. Regarding the differences in the definition of traffic collection between software, please refer to the article: TransCAD imports common traffic planning software collection data. Above, we combined the centroid connection interface with the east and west interfaces to specifically explain the application skills of the tools.
(1) Settings tab
[1] Connect TAZ
The TAZ here refers to the name of the traffic area layer. The user can modify the layer name and different names will be displayed on the interface. The traffic community layer can be a surface layer or a point layer (such as the geometric centroid of the traffic community). That is to say, when creating a centroid connection, it is not necessary to have a surface layer. It is worth pointing out here that it is easy for beginners to mistakenly confuse the geometric centroid of the traffic area with the centroid of the road network. Through the geographical file export function of TransCAD, the geometric centroid of the traffic area layer can be exported as a point layer. This point layer can also be used to create centroid connections. Many beginners think that these points are the centroids in the network. This is wrong! In fact, even if you use this point layer to create centroid connections, the generated The collection centroid is still an endpoint of the line connecting the centroids, not a point in this point layer. Therefore, it is completely redundant to derive the geometric centroid of the traffic community. Rwanda Sugar That’s it.
The “Application” drop-down menu is for the user to set which traffic conditions the community needs to create a shape Rwandans Escort. The default is all objects. , if the user defines a selection set of traffic cells, centroid connections can also be created for only some traffic cells. If users want to use different connection methods to deal with different traffic conditions, they can do it according to different clusters.
The “To” drop-down menu is the road segment layer name of which road network the user sets to connect to. If there are multiple road network layers in the map, the user must select one.
The “Maximum distance” edit box is the maximum length of the centroid connection set by the user, and the unit behind it is “public Rwandans Escort ri” is determined in the global settings of the software. We propose that the distance can be set larger, especially when there is no road network around some areas with traffic conditions, which can reduce the subsequent manual editing work.
The “Maximum number” edit box is the maximum number of centroid connections set by the user for each traffic cell/centroid. For example, 4 items are set, but it is possible that only 3 items are generated, and the fourth item exceeds the length setting. For the general city-level model, we propose to set up 4 to ensure the balance of traffic in each Rwandans Sugardaddy direction. For road condition impact assessment or partially refined models, we propose to set them up based on actual opening conditions.
[2] Connection requirements
TransCAD’s centroid connection can be connected to the nodes of the road network.It can also be connected to a road segment, which requires interrupting the road segment. For ordinary city-level models, we propose to connect to the nodes of the road network; for models of road condition impact assessment or partial refinement, we propose to connect to road segments according to actual openings.
The “Split segment belongs to” drop-down menu allows the user to set which road segments can interrupt the nodes connected as centroid connections. The user can create road segments in advance RW EscortsSelection Set. For example, users do not want to interrupt some high-level roads, or they may want to identify highways, rail lines and other road sections that are not suitable for connecting centroid lines.
“Split option” can choose “midpoint” and “vertical” modes. “Midpoint” means breaking at the center of the road segment, and “vertical” means breaking at the center of the road segment at the vertical projection. .
TIPs: In practice, the centroid connection method that automatically breaks road sections is rarely used, and refined models generally require manual intervention, such as the specific location of entrances and exits. In addition, if Rwandans Sugardaddy the road network is equipped with the bus system Route System, the bus connectivity must be checked in time. Is it just to connect to the node, or to interrupt the road segment and then connect to the interrupted node? If the road network is equipped with a public transportation system, we propose to back up the data in advance, and after generating the centroid connection, switch to the public transportation system layer in real time and replace it. New information Route System.
The “Endpoint connected to…” drop-down menu allows the user to set which nodes can be used as nodes connected by the centroid connection. The user can create a road segment selection set in advance. For example, users do not want to connect some advanced route nodes, rail traffic sites, etc. For strict specific models, the centroid connections of buses and motor vehicles may also need to be treated differently.
[3] Eliminate regulations
In addition to the connection road segments and node object selection set settings set in the connection regulations, you can also make selections Rwandans Escortset, clearly illustrates which road segments and nodes cannot be connected to the centroid connection. The user creates a selection set of road Rwanda Sugar segments and nodes in advance, in the “segments to be eliminated” and “endpoints to be eliminated” Just select from the drop-down list.
[4]Options
You can check “Limit centroid connections within the area”. For the traffic area layer, this option can be used when the road network density is high. The threshold can limit the spatial location of the connection point, such as the maximum distance outside the area. If it is too far, it will not be connected. The advantage of this is that when the road network is dense, you can connect several more centroids.When the network is sparse, there will be many fewer centroid connections.
(2) Change the new data tab
Using the method of breaking road segments, if you select road network aggregation in the “Split segment belongs to” drop-down menu, the interface will jump to the new segment attributes and replace them with new ones. Data tab, which is the same as the setting of the road network editing tool. The user can set how to handle the attributes of the fields after the road segment is interrupted, such as road name, speed, number of lanes, etc. Rwanda Sugar Daddy doors can be copied, the length is automatically divided in proportion, and other attributes such as time are also automatically divided in proportion (generally, new ones will be automatically replaced through the program later) Information, need not be considered).
(3) Fill tab
The purpose of the Fill tab is mainly to identify the centroid and centroid node in the road network.
[1] Fields to be filled
Users can create two fields in advance in the node and road segment layers. When the centroid connection is created, the values will be filled in these fields. So that you can easily select the centroid and the centroid connection in the future.
[2] Fill with…
Generally speaking, the initial values of the two fields created in advance in the node and road segment layers are empty, so filling them with a single value can be used for future identification, and they are not empty. is the line connecting the centroid and the centroid. You can also select “IDs from layer TAZ” to fill in the IDs of the traffic cell layer. After filling in this way, you can also use a non-empty query method to find the centroid and the centroid connection.
For the centroid, this value must be filled in meaningfully. It must be that the layer ID of the traffic area is exactly equal to the traffic area number defined by the user (such as TAZID. The user can re-export the dbd layer based on this field as the ID. ). If this is not the case, the following will describe how to relate the centroids and traffic cells in the traffic network.
4. TransCAD relates the centroid node and traffic area code in the traffic network
As mentioned below, it is assumed that we have completed the creation of centroids and centroid connections.. However, the TAZID of the centroid is filled with a single value. We do not know the corresponding relationship between the centroid and the traffic area. Here we introduce how to automatically connect the relationship. Assume that the TAZID field is created in the node layer. At present, the nodes at the centroid are filled with a single value of 1. The user encoding field is Zone_ID.
Step1: We can select things based on the centroid and select the centroid and the line connecting the centroid.
Step2: Open the node data table of the road network, and select the object collection of data records as “Centroids” in the main tool bar. In this way, the operation data is only for the nodes in the centroid collection.
Step3: Right-click the TAZID field and select “Fill” from the menu. Select the filling method as “Tag”, select the traffic area layer TAZ, the selection set is All Features, select the mark in the drop-down menu, and select the user encoding field of the traffic area layer TAZ as Zone_Rwandans EscortID. After clicking OK, the TAZID field obtains the information about the traffic area code Zone_ID, and the relationship is completed!
5. The traffic cell code of the relationship centroid node and the node database ID in the road network – matrix Rwanda Sugar DaddyIndex
To complete the last step of traffic allocation and bus allocation, it is necessary to associate the traffic cell code of the centroid node with the node database ID in the road network, which requires matrix index operation. The index number of the traffic dispatch and bus dispatch program demand matrix is based on the node database ID.
In Step 2 in the previous section, in the example of the node data table in the figure, the ID field of the centroid-aggregated database is exactly the same as the TAZID field value. This is a special situation. According to the traffic cell coding matrix, you can directly use Distributed based on traffic conditions. Of course, you can create a new ID field, such as IDD, and then number it according to your own preferences, and then use the geographical file import tool to export the dbd to reconstruct the ID you need. Just select IDD for the “Node ID Field” in the figure below. However, we don’t often use this method.
Under normal circumstances, the model network is continuously maintained, and the ID field of the database is automatically replaced with new data, which is different from the TAZID field value. At this time, you need to use the matrix index function. Since the traffic assignment and bus assignment matrix correspond to the ID field of the road network database, the data we obtain is generally a matrix organized according to the TAZID field. In traffic allocation and bus allocation, the problem to be solved by matrix index is to convert the matrix sorted by TAZID based on user coding into a matrix sorted by ID of the road network node layer database. In addition, the feature matrix (Skims) in the model is generally based on the road network node layer database ID, and the relevant model calculations must have a unified index.
Seeing this, the user will be confused, asking the user to add a matrix index workload. Does the software design have other considerations? In fact, the text begins with the traffic planning software’s management of centroids and centroid connections. In the method, an important reason has been mentioned, which is for the flexibility of defining the centroid of the traffic area. Of course, matrix indexes have many other uses. For more information about matrix indexes, please refer to the article: Deeply Understand TransCAD Matrix Index Conversion and Operation. The detailed matrix indexing method is discussed here, and I will not go into details in this article.
6. Conclusion
Through this article, I hope readers can understand the principle of centroid and centroid connection, the working mechanism in different software, and how to use the centroid connection in TransCAD something.
Add some internal things: the centroid connection can generally set the traffic capacity larger. If it replaces the internal path of the traffic partition, its attributes can be RW Escorts is set according to the actual situation. The centroid connections used for traffic distribution and bus distribution can be different, and their attributes are also different, for vehicles and pedestrians The speed is different (this has a particularly obvious impact on models with large road conditions). For Skim, we must also pay attention to the relevant characteristics on the centroid connection.
Many beginners will ask: “My road conditions.” Why does the distribution traffic result seem unreasonable? There is no traffic in some places, what should I do?”. Check the following tasks, and the general problem will be solved:
Is the OD matrix indexed?
There is no problem with the OD matrix itself Right?
Is it true that the centroid setting cannot be traversed?
The traffic area is small enough, how many numbers are connected to the centroids, and the connection method is reasonable?
Are the attributes of the centroid connections reasonable?
The road network is not congested. UE allocation is similar to shortest path allocation, resulting in no traffic on some road sections. This is not a matter of centroids and connections. Try using SUE allocation…
Original title: TransCAD centroids and centroid connections Those things
Article source: [WeChat official account: TransCAD and TransModeler traffic software] Welcome to add tracking and follow-up! Please indicate the source when transcribing and publishing the article
Review editor: Tang Zihong
Original title: Things about TransCAD centroids and centroid connections
Article source: [Microelectronic signal: TransCADTransModeler, WeChat public account: TransCAD and TransModeler road condition software Rwanda Sugar Daddy] Welcome to add tracking and care! Please indicate the source when the article is transcribed and published.
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