Repair Initial Coordinate System

btn_coord_sys_picker.pngAccessed in the Contents pane by clicking the coordinate system picker button for the component.

 

 

il_repair_initial_coord_sys.png

The Repair Initial Coordinate System command is used to correct errors in the assignment of an initial coordinate system.  Such errors usually occur in one of two ways:

 

 

 

Modern formats designed to store spatial data will automatically specify the coordinate system to be used for the data they provide.   Data from such sources will import seamlessly into Manifold with the initial coordinate system automatically assigned.  In the Contents pane the coordinate system for the component will appear in black text, indicating it has been assigned and the component is ready to go.

 

Sometimes there is an error in the source data.   For example, if a GIS operator wrongly specifies that a drawing uses Lambert Conformal Conic projection when it uses a Transverse Mercator projection, and then saves the drawing in a format that conveys coordinate system data, the file will wrongly state to every GIS that imports that drawing that it uses Transverse Mercator.  When imported into Manifold, the data will earnestly tell Manifold, with the full force and power and precision of the format, that it uses Lambert Conformal Conic and Manifold will believe it.   

 

The drawing ends up imported into Manifold marked as having Lambert Conformal Conic as the assigned initial coordinate system.  Until we try to use that drawing as a layer together with other drawings or images which are not in error, we might not notice the mistake.  When we do notice the mistake we can use the Repair Initial Coordinate System dialog to change the assigned initial coordinate system to the correct Transverse Mercator coordinate system.

 

A more frequent use of the Repair Initial Coordinate System command is to repair errors made with the Assign Initial Coordinate System dialog.  Sometimes we must import data that we know is projected but which is stored in a format that does not specify projection (coordinate system) information.   In such cases we might use the Assign Initial Coordinate System dialog to try a best guess, for example Latitude / Longitude.    If that does not result in the imported drawing correctly lining up with other, "known good" layers, we might want to try some other guesses.   For those we can use the Repair Initial Coordinate System command.

 

A related case is when we use Assign Initial Coordinate System to assign the initial coordinate system and we get most, but not all, of the coordinate system right.   For example, we might try a default favorite coordinate system, Latitude / Longitude, and see that everything seems to line up OK.    The default Latitude / Longitude coordinate system built into Manifold's Favorites list uses WGS84 as the datum, but there is a vast amount of spatial data in the world that uses other datums, such as NAD27.   

 

The difference between the two datums is not that much, but it can be significant, as discussed in the Latitude and Longitude are Not Enough essay.  If we later discover that our imported drawing was indeed in Latitude / Longitude, but in a form that used the NAD27 datum, we can use the Repair Initial Coordinate System command to adjust the assigned initial coordinate system to use the NAD27 datum.

 

btn_coord_sys_picker.pngRepairing an initial coordinate system is easy: Click the coordinate system picker button in the Contents pane and under Repair Initial Coordinate System unfolds a menu that allows one of three choices:

 

 

 

 

See the Coordinate System topic for details on using that dialog.

 

 

 

Using the Repair Initial Coordinate System dialog is similar to using the Assign Initial Coordinate System command.  For a step-by-step illustrated example using the Assign Initial Coordinate System command, see the Example: Assign Initial Coordinate System topic.

Notes

Synonyms -  The terms projection and coordinate system are used as interchangeable synonyms in Manifold.  Cartographers favor the term projection while programmers seem to prefer coordinate system.  This documentation uses the two terms interchangeably, with the term projection tending to be used more in GIS or display contexts and the term coordinate system tending to be used more when discussing programming, SQL or standards.

 

See Also

Coordinates

 

Projections

 

Assign Initial Coordinate System

 

Change Coordinate System

 

Map Projection

 

Coordinate System

 

Base Coordinate System

 

Favorite Coordinate Systems

 

Favorite Base Coordinate Systems

 

Example: Assign Initial Coordinate System - Use the Contents pane to manually assign an initial coordinate system when importing from a format that does not specify the coordinate system.

 

Example: Change Projection of an Image - Use the Change Coordinate System command to change the projection of an image, raster data showing terrain elevations in a region of Florida, from Latitude / Longitude to Orthographic centered on Florida.

 

Example: Adding a Favorite Coordinate System - Step by step example showing how to add a frequently used coordinate system to the Favorites system.

 

Example: Detecting and Correcting a Wrong Projection - A lengthy example exploring projection dialogs and a classic projection problem.  We save a drawing into projected shapefiles and then show on import how a projection can be quickly and easily checked and corrected if it is wrong.

 

Re-Projection Creates a New Image - Why changing the projection of an image creates a new image.

 

About Coordinate Systems

 

Projections Tutorial