Use this dialog to specify units, unit scale and factors such as local scales and local offsets.
The Coordinate System dialog's "XY" metrics picker button provides a choice of Use Default Metrics or Edit Metrics.
The Edit Metrics choice launches the Coordinate System Metrics dialog. The Use Default Metrics choice resets metrics to the default values for the coordinate system. If coordinate system metrics are already set to the default values, the command is displayed with a check icon.
XY and Z units |
Unit of measure currently in use by this coordinate system. Choose a different unit from the long list. |
Custom unit scale |
Check this box to specify a custom unit that is scaled differently than the standard definition. For example, some data sets might use a "foot" that is slightly longer than what is considered to be a standard foot. Checking this box will mark the unit abbreviation used with an asterisk * character, as in ft*. |
Local scale X |
The local scale transformation to apply to X values. For example, an image might have 10 pixels per degree and thus a Local scale X of 0.1 would be used in degree-based coordinate systems, such as Latitude / Longitude systems. |
Local scale Y |
The local scale transformation to apply to Y values. For example, an image might have 10 pixels per degree and thus a Local scale Y of 0.1 would be used in degree-based coordinate systems, such as Latitude / Longitude systems. |
Local offset X |
An absolute value to add or to subtract in the X direction. For example, if an image with pixels that are 30 meters wide by 30 meters tall has coordinates specified for the exact center of each pixel, to adjust those coordinates to the lower left corner origin of pixels in Manifold we would use a -15 value for Local offset X. |
Local offset Y |
An absolute value to add or to subtract in the Y direction. For example, if an image with pixels that are 30 meters wide by 30 meters tall has coordinates specified for the exact center of each pixel, to adjust those coordinates to the lower left corner origin of pixels in Manifold we would use a -15 value for Local offset Y. |
Local scale Z |
The local scale transformation to apply to Z values. |
Local offset Z |
An absolute value to add or to subtract in the Z direction. |
Click to open a dropdown menu with two choices to alter the parameter:
Use Default Value- resets the parameter to the default value. If the parameter is already set to the default value, a check icon will appear next to the Use Default Value command.
Unit Converter - Launch the Unit Converter dialog to allow easy conversion of units and values for this parameter. |
In the Coordinate System dialog, false easting and false northing parameter values (for those coordinate systems that use those parameters) will be displayed in the units of measure specified for the coordinate system. Changing units of measure for a custom coordinate system will automatically re-scale false easting and false northing values to the new units.
We can specify a custom unit scale for data sets which use a unit definition that is slightly different than standard unit definitions as used within Manifold.
Suppose we are working with a data set from a country where a "foot" is considered to be slightly larger than what usually is thought to be a standard foot.
We can change the definition of a Foot for this particular coordinate system from 0.3048 meter to 0.3050 meter. After this adjustment, the abbreviation for the unit of measure in this coordinate system will be shown with an asterisk * character, as ft*.
See the Example: Convert a 0 to 360 Degree Projection topic for a real life example using this dialog.
Metrics values - Choosing a coordinate system in the main Coordinate System dialog will load the Coordinate System Metrics parameters with the correct values for the chosen system. Those are usually based on a unit of 1 meter or 1 degree, but some national coordinate systems use values like 0.9 meter. Custom values as read from a world file or entered manually will also appear.
EPSG and SRID Overrides - EPSG and SRID coordinate systems use a numeric code to identify the coordinate system. Metrics for EPSG and SRID coordinate systems are applied as overrides. This allows keeping the coordinate system definition as a code for readability and for easier conversion.
Exports - When exporting vector data, the system will set local scales to 1 unit of whatever is the current coordinate system unit.
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 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.
Latitude and Longitude are Not Enough