Aimsun Next Coordinate System¶
Any coordinate system can be used by Aimsun Next with two conditions: First that it uses meters as its units and second that all data uses the same coordinate system. Data imported by Aimsun Next will be converted as as part of the importing process which means that points in decimal degrees will be projected to a projected coordinate system and data in a projected coordinate system in units other than meters will be transformed.
The first step when creating a new model is to select the coordinate system. Before version 8.1,the UTM coordinate system based on the WGS84 ellipsoid (EPSG in the range 32601 to 32760) was expected, but from release 8.1, any coordinate system can be used provided it is in meters.
The options when to set the coordinate system are:
1) When creating a new document, select the co-ordinate system in the Welcome dialog.
2) Any time after creating a new document by using the Project editor accessible from the Project menu.
3) When importing new data, by selecting the coordinate system of the imported data.
In cases 1 and 2 Aimsun Next will request the EPSG code that determines the coordinate system. Alternatively this information can be supplied as a OGC WKT string. The Spatial Reference web site lists the coordinate systems that can be used in Aimsun Next.
In both cases Aimsun Next includes a dialog to calculate the EPSG code from a UTM zone.
After importing or editing data, a change in the coordinate system will not make Aimsun Next re-project the current data. Hence, the coordinate system must be set before adding any geographic information.
When selecting a file to import that includes geographic information the data must be changed to use the current coordinate system or the data can be imported as they are and set the data coordinate system as the new one.
Selecting a coordinate system for imported data in a document that already has information using a different coordinate system will not work. Data will be imported but old data will be now placed at the wrong location (when they are exported as decimal degrees) and old data and new data will be misplaced relative to each other.
What Coordinate System choose?¶
Usually an Aimsun Project will start by importing some information: a project from a different software, CAD drawings or GIS data. It is recommended that the a coordinate system is selected that will make it easy to share information. The coordinate system of the imported data is a usually a good choice. However, consider that:
1) Aimsun Next requires meters as the units of its coordinate system. If the imported data uses data in other units, the data will be transformed. In this case, select a coordinate system before importing or let Aimsun Next select one based on the UTM zone.
2) If the imported data uses decimal degrees, they will be projected.
3) If the imported data uses units other than meters, they will be transformed. If the data has a known coordinate system, the data will be re-projected. If this is not available, Aimsun Next can only scale data from feet to meters.
A new project is started importing data that uses the coordinate system NAD 1983 StatePlane New York Long Island FIPS 3104 Feet. As this coordinate system is in feet the data must be transformed during the import process.
Before importing it, a suitable coordinate system must be selected. One candidate is UTM, in this case zone 18 northing. Other is NAD 1983 HARN StatePlane New York Long Island FIPS 3104 as this one uses meters. The data is now imported and converted.
Aimsun Next can export data in either the original coordinate system or transforming it to decimal degrees. In this second case, it will use WGS 84.