The Repair Initial Coordinate System command is accessed in the Component pane by clicking the coordinate system picker button for the component.
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:
The source format specified the wrong initial coordinate system.
The user manually specified the wrong initial coordinate system using the Assign Initial Coordinate System dialog.
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 Component 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.
Repairing an initial coordinate system is easy: Click the coordinate system picker button in the Component pane, and click Repair Initial Coordinate System to unfold a menu that allows further actions:
(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. |
Copy |
Copy the current coordinate system to the Windows Clipboard. |
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. |
Using the Repair Initial Coordinate System dialog is similar to using the Assign Initial Coordinate System dialog. For a step-by-step illustrated example using the Assign Initial Coordinate System dialog, see the Example: Assign Initial Coordinate System topic.
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.
Assign Initial Coordinate System
Favorite Base Coordinate Systems
Example: Convert a 0 to 360 Degree Projection - We often encounter data, both images and drawings, using latitude and longitude degrees that appears to be in Latitude / Longitude projection but which has longitude values from 0 degrees to 360 degrees and latitude values from 0 degrees to 180 degrees, instead of the usual arrangement of -180 degrees to 180 degrees for longitude centered on the Prime Meridian, and -90 degrees to 90 degrees for latitude centered on the Equator. This example shows how to utilize such data by assigning the correct projection.
Example: Assign Initial Coordinate System - Use the Component 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 Reproject Component 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.
Reprojection Creates a New Image - Why changing the projection of an image creates a new image.