Coordinate systems

When creating networks, components from different GIS sources are often combined, which partially refer to different coordinate systems. To make the data consistent a coordinate transformation is necessary. Visum supports you with this task with the following functions.

  • The user can optionally specify that all coordinates in the current network belong to a predefined coordinate system (User Manual: Selecting a coordinate system).
  • The coordinate system can be changed in Visum. You can automatically transform the coordinates of the current network (User Manual: Selecting a coordinate system).
  • If data is imported, which refers to another coordinate system than that for the current network, Visum automatically transforms the imported coordinates into the system of the current network.

There is an option to switch from the default Visum to a predefined coordinate system. Visum offers a selection of coordinate systems, which are provided as files with the extension *.prj. You can find them in the directory ...\Program Files\PTV Vision\PTV Visum 2021\Exe\Projections. This file format is the Well Known Text format in the ESRI version.

Note: You can optionally specify, whether you want to work with a current projection in your project. It is usually sufficient to keep the standard setting ("Visum"). In this case coordinates in Visum do not apply to any current projection, but are illustrated "uninterpreted" in a rectangular system. If, however, original files are specified in a certain projection and are imported to a network, where no projection has been selected, the display is distorted. In this case select the suitable projection.

In Visum, a difference is made between geographic coordinate systems and projected coordinate systems.

In geographic coordinate systems, the coordinates are displayed as spherical coordinates with geographic length and width. They are measured as an angle from the earth's center to a point on the earth's surface (for example 47° 6‘ northern latitude, 12° 27‘ eastern longitude). In comparison, the coordinates of the earth ellipsoid is projected to a level, for plane coordinate systems. A location on earth is therefore distinctly determined as an X and Y coordinate on the level. The following example shows two projection files for a planar and a geometric coordinate system in Visum.

Example for planar coordinate system (WGS 1984 UTM Zone 48N.prj)

Table 286: Planar coordinate system

 
PROJCS["WGS_1984_UTM_Zone_48N",
GEOGCS["GCS_WGS_1984",
DATUM["D_WGS_1984",
SPHEROID["WGS_1984",6378137,298.257223563]],
PRIMEM["Greenwich",0],
UNIT["Degree",0.017453292519943295]],
PROJECTION["Transverse_Mercator"],
PARAMETER["False_Easting",500000],
PARAMETER["False_Northing",0],
PARAMETER["Central_Meridian",105],
PARAMETER["Scale_Factor",0.9996],
PARAMETER["Latitude_Of_Origin",0],
UNIT["Meter",1]]

Example for geographic coordinate system is the German Main Triangle Network (Deutsches Hauptdreiecksnetz.prj):

Table 287: Geographic coordinate system

 
GEOGCS["GCS_Deutsches_Hauptdreiecksnetz",
DATUM["D_Deutsches_Hauptdreiecksnetz",
SPHEROID["Bessel_1841",6377397.155,299.1528128]],
PRIMEM["Greenwich",0],
UNIT["Degree",0.017453292519943295]]

Note: Please note, that in the actual file *.prj the projection properties which are written down row by row, have to be successive (in a row). Detailed information on how to create projections can be found on the ESRI webpage (for example at www.support.esri.com/index.cfm?fa=knowledgebase.techArticles.articleShow&d=14056).

Visum manages coordinate systems in the following file types: Depending on the file type, coordinate information is saved or imported differently.

File type

Save

Read

*.ver Version file

All attributes of the current coordinate system are saved.

All attributes of the current coordinate system are read in. If the name of the system is not found in the list of predefined systems, it is added to the selection. A *.prj file is not created.

*.net, *.mdb, *.accdb Network file database

All attributes of the current coordinate system are saved.

If not read-in additionally, the file is read like a version file, in case the network parameter block is missing, the standard setting (Visum) is applied. If read-in additionally, the network parameters block is read-in in case it exists and is enabled (User Manual: Reading network data additively).

*.shp Shape file

In addition to the shape file, a *.prj file with the currently set projection is created if it differs from the standard setting (Visum).

If a corresponding *.prj file exists for a shape file, it is used as projection and transformed into the currently set projection if applicable. If it does not exist and the existing network has a coordinate system, the user selects a coordinate system (User Manual: Importing Shapefiles).

*.inpx Vissim network

The coordinates are written to the *.inpx file without further transformation.

not applicable

*.hgr Background file

not applicable

Background files are not adjusted.