Change Coordinate System

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

 

We use Change Coordinate System to re-project the data in a component into a new coordinate system.  The terms projection and coordinate system are used as interchangeable synonyms in Manifold.

 

The Change Coordinate System command in the Contents pane launches the Change Coordinate System dialog.   This dialog is used to change the projection of an image or drawing that already has had the initial coordinate system set correctly, either automatically upon import or manual assigned using the Assign Initial Coordinate System command.

 

If the coordinate system read out in the Contents pane uses red text then the initial coordinate system has not yet been assigned and the Change Coordinate System command will be disable. To enable the Change Coordinate System command we must first use Assign Initial Coordinate System to specify the initial coordinate system.

 

The Change Coordinate System dialog shows the current coordinate system in use and allows us to specify a new coordinate system to be used.    The dialog provides us two options for re-projecting the component:

 

 

 

To change the projection of an image or drawing:

 

  1. Open the image or drawing.

  2. In the contents pane press the coordinate system picker button and choose Change Coordinate System to launch the Change Coordinate System dialog.

  3. Press the coordinate system picker to choose the new coordinate system desired.  This allows a quick pick from the listed favorites or choosing Edit Coordinate System to launch the full Coordinate System dialog that allows a choice of thousands of systems.

  4. In the Change Coordinate System dialog choose how the new coordinate system will be applied:

 

See the Example: Change Projection of an Image topic for a step-by-step example.

 

The  Change Coordinate System process changes the coordinate data within the component into a new coordinate system and also updates the projection assigned to the component.  The dialog appears with drawing and image windows but does not appear with map windows, since map windows are just viewports into the layers they display and do not themselves contain any data.  To change the projection used by a map window, we use the Map Projection dialog.  See the discussion in the Projections topic.

 

For drawings, changing the projection changes the coordinate numbers embedded in the drawing's geometry.  For images, changing the projection will change the number of pixels to interpolate coverage by pixels over the new shape of the image in the new coordinate system.  

 

Because the number of pixels and thus tiles will change changing the projection of an image is always an Add Component operation to create a copy of the image in the new projection form.  See the Re-Projection Creates a New Image topic for why re-projecting an image changes the number of pixels.

Change Coordinate System Dialog

Choosing Change Coordinate System in the Contents pane launches the Change Coordinate System dialog.

 

eg_change_proj_image01_02.png

Controls

Current

The current coordinate system used by this component.

New

The new coordinate system into which this component's data should be re-projected.

btn_coord_sys_picker.png

Click to choose the new coordinate system desired.  This allows a quick pick from the listed favorite coordinate systems  or choosing Edit Coordinate System to launch the full Coordinate System dialog that allows a choice of thousands of systems.

Allow parallel execution

If checked (default) the re-projection computation will use CPU parallelism in multiple threads on as many CPU cores as are available for faster performance.   Checking this box is equivalent to commanding THREADS SystemCpuCount() in SQL in templates that utilize parallelism.

Update Component / Add Component

Push this button to command the re-projection.

 

Choose either the Update Component or Add Component setting by pulling down on the down arrow button.

 

  • Update Component - Apply changes to the current drawing.  Drawings only - not available for images..

 

  • Add Component - Create a new component that copies the context component into a new, re-projected component.  Available for drawings and images.

Edit Query

Click to open the Command Window pre-loaded with an SQL query which accomplishes the re-projection as specified and given the choice of Update Field or Add Component.

Close

Close the dialog

 

btn_coord_sys_picker.pngIn the Change Coordinate System dialog click the coordinate system picker button to choose a new coordinate system.   The default favorites and any other favorites we have added will appear in a list, along with an Edit Coordinate System option to launch the full  Coordinate System dialog.

 

When finished choosing a new coordinate system we press OK to exit the Coordinate System dialog and return to the Change Coordinate System dialog.  We can then either update the existing component if it is a drawing or add a new component to the project that is re-projected into the new coordinate system.

 

See the Coordinate System topic for information on choosing a new coordinate system.

Notes

Synonyms -  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.

 

 

Bases are Basic - All coordinate systems are based upon a model of the Earth's sphere or ellipsoid that specifies the size and shape of the Earth using various parameters such as radius, eccentricity, center of rotation and so on.   Such models have usually been referred to by cartographers and GIS people as the ellipsoid or datum but the more popular term among computer people now is becoming the base, short for base coordinate system.  Manifold tends to use the terms base, base coordinate system, ellipsoid and datum as interchangeable synonyms since that is how most people working with spatial data know the terms.  

 

All spatial data in any projection, including Latitude / Longitude, assumes some base even if the base is not explicitly specified as is often the case with data where latitude and longitude numbers specify a location.   If precision is required it is important to know what base is assumed because different bases used with exactly the same type of coordinate system and exactly the same numeric data can result in differences of hundreds of meters in the position of a location.   

 

We might not care about what base was used if we are creating maps that display all of Europe where it does not matter if the dots that represent cities vary in position by a few hundred meters, but in other applications such as guiding an emergency medical response vehicle to the correct entry portal for a hospital and not into water in an adjacent lake, or determining whether a specific real estate parcel falls within a special planning zone or taxation zone, a few hundred meters can matter very much.   See the Latitude and Longitude are Not Enough topic for a visual example of how varying bases can move the position of exactly the same coordinates.

See Also

Coordinates

 

Projections

 

Assign Initial Coordinate System

 

Repair Initial 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.

 

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

 

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.

 

About Coordinate Systems

 

Projections Tutorial

 

Latitude and Longitude are Not Enough