Coordinate system: Projected coordinate system

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Create Projected Coordinate system

The Projected coordinate system is used to define XY-coordinates of a map by specifying its boundaries, projection, ellipsoid and/or datum. Maps with different coordinate systems and different projections can be transformed into one another while maps missing projection information cannot be transformed into any other coordinate system.
A new coordinate system including projection information can be created via ILWIS-Python editor or can be directly created using ILWIS 4 user interface/create toolbox tab.
Using Python, a coordinate system objects can be created from a Proj4 definition, from their EPSG code or from an existing coordinate system file.The required Python syntax to create a projected coordinate system are:


From proj 4 definition:
name of the output coordinate system = ilwis.CoordinateSystem("project 4 definition")

From: EPSG code:
name of the output coordinate system = ilwis.CoordinateSystem("code=epsg:number")
From an existing file:
name of the output coordinate system = ilwis.CoordinateSystem("name of the existing file")


Then, the Python syntax for the above mentioned create operation looks like example below:


From proj 4 definition:
output = ilwis.CoordinateSystem("code=proj=utm +zone=37 +ellps=WGS84 +units=m +no_defs")
From: EPSG code:
output = ilwis.CoordinateSystem("code=epsg:23035")
From an existing file:
output = ilwis.CoordinateSystem("countries.csy")


The Project 4 definition parameters used in the example above are:
+proj Projection name
+zone name of the UTM zone
+ellps Ellipsoid name
+units name of the unit employed which is meters in this example
+no_defs Don't use the /usr/share/proj/proj_def.dat defaults file

Note that, the GPES codes are listed in ILWIS create projected coordinate system form, however, the codes and detailed information can also be found online: https://epsg.io/ If you use the epsg website, make sure choosing the code that has the compatible projection and datum/ellipsoid with the rest of your data. Information related to project 4 definition can be derived online from: http://spatialreference.org/. The list of input parameters for Proj4 definition is also available online at: http://proj4.org/parameters.html Note that ILWIS-Python extension does not support all the listed input parameters.

Once the coordinate system is created you can define its boundaries by assigning the X and Y minimum/maximum coordinates to it by creating an envelope; it is not required, but optional. However, in case you decided to set the boundary coordinates make sure that the boundary is within the range of the coordinates derived from the EPSG or project 4 codes. The following Python syntax can be used to create an envelope:


name of the output envelope = ilwis.Envelope(ilwis.Coordinate(min/max coordinates of lower left corner),ilwis.Coordinate(min/max coordinates of upper right corner).


You may also use min/max coordinate of upper right and lower left coordinates as well. The Python syntax for creating an envelope looks like example bellow:


env=ilwis.Envelope(ilwis.Coordinate(696275.4000, 9797373.3700),ilwis.Coordinate(813775.4000, 9885123.3700))


The next step is to assign the envelope to the already created coordinate system using the following Python syntax:


output.setEnvelope((env))

Figure 1, Create projected coordinate system form; (A) by EPSG number, (B) by project 4 definition and (C) by full definition


To directly create a coordinate system via ILWIS user interface, Click the “Create” button in main window and select a desired coordinate system from the available list in “Object creation” form. Once an object is selected from the list, an object creation form will be opened in which you can set parameters required for the operation (Figure 1). This example, shows how to create a "Projected coordinate system". Once this option is selected from the list, the "Project coordinate system" form will be opened. The form includes three radio buttons allowing users to create the coordinate system using different methods. The inputs parameters varies depending on the methods by which the projected coordinate system will be created. Figure 1 shows the three forms: Fig. 1A, shows the form related to the method "By EPSG number", Fig. 1B illustrates the form related to the method "By project 4 definition" and Fig. 1C shows the form related to the method "Full definition". To successfully execute this operation, you need to complete the form with proper inputs data.

Dialog box options:

Name: Enter a name for the coordinate system. As one coordinate system is used for all maps with the same projection, it is advised to enter a coordinate system name that applies to all maps (the name of the country, region, project, etc.).
Description: Optionally, type a description for the coordinate system. The description is visible on the status bar of the Main window when moving the mouse pointer over the coordinate system in the Catalog.
Projected coordinate system methods: Select one of the three available methods: By EPSG number, By project 4 definition and by full definition.
Apply: Click the “Apply“ button to create this object.
Close: Click the “Close“ button if you like to cancel the create operation.


When selecting the option "By EPSG number", a list of "EPSG number" will appear on the form. you have to select the correct EPSG number that represents the location of your area. More information on the ESPG number are available on: https://epsg.io/ or http://spatialreference.org/ . When selecting the option "By project 4 definition", you need to manually enter the input data. You can get the Project 4 data from: http://spatialreference.org/ . When selecting the option "Full definition", from the list you can select a projection type and depending of that various type of inputs are required. For example, if you select "UTM" as the projection, then you will be asked to enter the UTM zone and if select "Transvers Mercator" or "Azimuthal Equidistance", then you need to enter the following inputs:

  • False easting (the python input syntax: +x_0)
  • False northing (the python input syntax: +y_0)
  • Central meridian
  • Latitude of origin
  • Scale factor
  • Southern hemisphere UTM zone (the python input syntax: +south)
  • Datum name (the python input syntax: +datum)
  • UTM zone(the python input syntax: +zone)