Assign Coordinate System

Some file formats, such as CAD formats, do not specify the coordinate system used by the data they contain.  

 

When importing or linking data from such formats, Manifold will detect that a source failed to provide coordinate system information.  The system will assign a temporary placeholder coordinate system of Pseudo-Mercator, and will report that coordinate system in the Info pane using red text to alert us that it is just a placeholder.

 

Before using that data we must specify the projection manually by launching Assign Initial Coordinate System in the Info pane.

 

When Importing or Linking from non-spatial formats:

 

  1. Import or Link the file.

  2. Open the drawing or image.

  3. In the Info pane, click the coordinate system picker button to launch Assign Initial Coordinate System.

  4. Specify the coordinate system used by the data.

 

Always do the above procedure when importing or linking drawings or images from formats which do not specify the projection used for the data.  This includes all shapefiles not accompanied by a .prj file.  

 

The Assign Initial Coordinate System choice appears in the coordinate picker button's menu only when the coordinate system is shown in red color.  The red color indicates the initial coordinate system has not yet been assigned.

 

 

 

Assigning an initial coordinate system is easy: Click the coordinate system picker button in the Info pane Component tab, choose Assign Initial Coordinate System and that opens a menu that allows easy specification of the desired coordinate system.

 

 

The menu provides frequently used Favorites which we can choose with one click.  It also provides a More... command to allow choice from thousands of coordinate systems or custom specification of a new coordinate system.

 

(Favorites List)

A list of favorite coordinate systems.  Factory defaults are Pseudo-Mercator and Latitude / Longitude.  Add or delete favorites as desired.

More...

Launch the full Coordinate System dialog that allows a choice of thousands of systems.

Favorites

Add, delete, or modify favorite coordinate systems.

Paste

Paste a coordinate system from the Windows Clipboard.

Paste without Metrics

Paste a coordinate system from the Windows Clipboard, but do not apply the Coordinate System Metrics it specifies.

 

Used Only Once

 The Assign Initial Coordinate System command is used only once after initial import or linking of a component.  After it is used once the command will no longer appear.   If we make an error applying this command, we can repair the error by using the Repair Initial Coordinate System command that will be available.

 

For a step-by-step illustrated example using the Assign Initial Coordinate System command, see the Example: Assign Initial Coordinate System topic.

Notes

No changes to data - Assigning an initial coordinate system does not change the coordinate numbers embedded in a drawing's geometry and it does not change pixels in images.   It only tells the system what coordinate system to assume when interpreting that data.   The only change is to the coordinate system property for the data.

 

Difficulties - There are two difficulties using Assign Initial Coordinate System:

 

Knowing what to assign - People publish projected data all the time in old formats which do not convey projection information, and then they fail to tell users what projection they  used.    

 

The red text along with a choice limited to Assign Initial Coordinate System warns us that the source of the data failed to specify the coordinate system, but if we do not know from other means (such as reading a description of the data on a web site) what coordinate system should be used we cannot manually assign it using the command.

 

The best approach is to sharpen our detective skills, to carefully search the website from which we downloaded the data and to carefully review any accompanying metadata files to see if we can find an authoritative statement of what coordinate system was used.

 

Human error - People who do not read instructions may misuse Assign Initial Coordinate System by thinking it is used to change a coordinate system that has already has been correctly assigned.   The result is total chaos because first, the initial coordinate system has now been wrongly assigned, and second, the red text that was used to warn that the coordinate system was probably wrong will now be replaced with black text, giving the impression that the (probably wrong) coordinate system is correct.  

 

Such errors take a perfectly good image or drawing that was ready to be made useful through intelligent use of Assign Initial Coordinate System, and instead will ruin it by assigning the wrong coordinate system to that data.  

 

Managers should prevent this problem by teaching beginners to pause when they see red text and the sole choice of Assign Initial Coordinate System.  They should not do anything further without consulting somebody who knows what they are doing.   Forbid untrained users from using Assign Initial Coordinate System until their work can be reviewed by a knowledgable user, or until they have learned enough not to misuse the command.

 

 

 

Next:  Change Coordinate System