Coordinate system: Latlon coordinate system

From ILWIS
Jump to: navigation, search
Main Page Arrow.png Operations Arrow.png Create objects Arrow.png Coordinate system Arrow.png
Boundary only coordinate system Projected Coordinate system Geographic coordinate system
Create Projected Coordinate system

A Geographic coordinate system defines LatLon-coordinates for maps by specifying the boundaries of the map area in Latitudes and Longitudes and optionally ellipsoid and/or datum information. A new Latlon coordinate system can be directly created using ILWIS 4 user interface/create toolbox tab or can be created via ILWIS-Python editor. The required Python syntax is:


name of the output coordinate system = ilwis.CoordinateSystem("")


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


output = ilwis.CoordinateSystem("")


The coordinate system can also be created using GPES number as it described bellow. The GPES codes are listed in ILWIS create projected coordinate system but also you can find them 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 and epsg codes can also be derived online from: http://spatialreference.org/. The Python syntax for using epsg code looks like example below:


cosys = ilwis.CoordinateSystem("code=epsg:32736")


Once the coordinate system is created you can assign the minimum/maximum of 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 coordinate of lower left corner),ilwis.Coordinate(min/max coordinate 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:


cosys.setEnvelope((env))

File:Lat.png
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
  • False northing
  • Central meridian
  • Latitude of origin
  • Scale factor