To define a coordinate system
-
Click
. Find
- In the Create Coordinate System Wizard, on the Specify Starting Point page, specify whether to start with a coordinate system, or to first define or edit an ellipsoid or a datum. Then click Next and follow the directions in the appropriate procedure below.
If you begin by defining a datum or ellipsoid, you can start from scratch or edit an existing datum or ellipsoid and save it as a new entry. Once you define the datum and/or the ellipsoid, you continue through the process of defining a new coordinate system.
If you begin by editing an existing coordinate system, you start by assigning it a code and description. This copies the information from the existing coordinate system into a new one, and leaves the original coordinate system unchanged.
To start with an ellipsoid
- On the Specify Ellipsoid page of the wizard, select Create A New Ellipsoid or Create A New Ellipsoid From An Existing Ellipsoid and click Next .
If you are using an existing ellipsoid, specify the ellipsoid that will be the basis of the new one.
- On the Create/Modify Ellipsoid page, enter a Code.
The code must be unique within a category and across all coordinate systems and must not contain spaces. Only the following characters are valid: A-Z (upper or lower case), 0-9, dash, and underscore.
- Enter a Description.
AutoCAD Map 3D displays the description in the Coordinate System Library.
The remainder of the fields in the wizard are pre-populated if you are using an existing ellipsoid. For a new ellipsoid, they are blank. In either case, you can specify new values.
- Specify the following:
- Create An Ellipsoid/Sphere: If you select Create An Ellipsoid, you must complete all four values. However once you enter Equatorial Radius and one other value, the remaining values are filled in automatically. If you select Create A Sphere, you must enter a value for Equatorial Radius only.
- Equatorial Radius: Specify the equatorial radius in meters. The equatorial radius is also called the semi-major axis.
- Inverse Flattening: Speciy the denominator of the flattening ratio. That is, if the flattening ratio is 1/x, specify x.
- Polar Radius: Specify the polar radius in meters. The polar radius is also called the semi-minor axis.
- Eccentricity Squared: Specify the eccentricity as a real number.
- Click Next to continue creating a coordinate system that uses the ellipsoid you just defined. You have the option to create or modify a datum for the coordinate system.
To start with a datum
- On the Specify Datum page of the wizard, select Create A New Datum or Create A New Datum From An Existing Datum and click Next .
If you are using an existing datum, specify the datum that will be the basis of the new one.
- On the Create/Modify Datum page, enter a Code.
The code must be unique within a category and across all coordinate systems and must not contain spaces. Only the following characters are valid: A-Z (upper or lower case), 0-9, dash, and underscore.
- Enter a Description.
AutoCAD Map 3D displays the description in the Coordinate System Library.
The remainder of the fields in the wizard are pre-populated if you are using an existing datum. For a new datum, they are blank. In either case, you can specify new values.
- Specify the following:
- Ellipsoid: Enter or select the ellipsoid on which this datum will be based.
- Source: Enter the data source from which the values for this datum were taken.
- Click Next to continue creating a coordinate system that uses the datum you just defined.
To define a coordinate system or edit an existing one
- On the Specify Coordinate System page of the Create Coordinate System Wizard, select Create A New Coordinate System or Create A New Coordinate System From An Existing Coordinate System and click Next .
If you are creating a coordinate system from scratch, select the Coordinate System Type.
- Projected: Uses linear units, such as meters and feet.
- Geographic: Uses angular units, such as degrees, radians, grads, and mils. See the Concept tab of this topic for definitions of projected and geographic coordinate systems.
- Arbitrary: A non-earth (NERTH) coordinate system. No ellipsoid or datum is required.
If you are using an existing coordinate system, specify the coordinate system that will be the basis of the new one.
- On the Create/Modify Coordinate System page, enter a Code.
The code must be unique within a category and across all coordinate systems and must not contain spaces. Only the following characters are valid: A-Z (upper or lower case), 0-9, dash, and underscore.
- Enter a Description.
AutoCAD Map 3D displays the description in the Coordinate System Library.
The remainder of the fields in the wizard are pre-populated if you are using an existing coordinate system. For a new coordinate system, they are blank. In either case, you can specify new values.
- Specify the following:
- Source: Enter the data source from which the values for this coordinate system were taken, for example, Snyder, J.P., Map Projections - A Working Manual.
- Unit: Select the units to use for this coordinate system.
- Categories: Select the category (or categories) in which this coordinate system will appear. Click the category name in the left-hand list and click Add to move it to the right-hand list.
You can filter the list of coordinate systems in the Coordinate System Library by category.
- Under Referenced To, do one of the following:
- To base the coordinate system on a datum , select Geodetic. Click Select to specify the datum.
- To base the coordinate system on an ellipsoid , select Non-geodetic. Click Select to specify the ellipsoid.
- To create a coordinate system that is neither geodetic nor non-geodetic, click None.
Use this option to create a non-Earth or arbitrary coordinate system.
- Click Next to see the Specify Projection page of the wizard.
- On the Specify Projection page, select a projection, set its parameters, and click Next.
The projection you choose determines how many projection parameters you must enter and the units you can use. The exact fields vary according to the projection you select. For more information, see Create Coordinate System Wizard.
- On the Specify Common Parameters page of the wizard, specify the remaining parameters and click Next.
In a few cases, these parameters will not appear.
- For Scaling, specify the paper scale for the coordinate system. For most GIS systems, this is 1 because virtual maps are not limited to paper size.
- For Quadrant, specify the quadrants in which the x- and y-coordinates are positive (usually East and North).
- For Useful Range, specify the minimum and maximum latitude and longitude for which this coordinate system is considered valid.
- For Minimum Non-Zero Coordinate Values, enter the lowest x, y values found in the positive quadrants.
- On the Review Coordinate System page of the wizard, review your settings. If you need to change any of them, click Edit next to that group of settings. When the settings are correct, click Finish.