6.1 Projection Manager

The Projection Manager allows you to choose, edit and save map projections
for use in Unidata applications.
A **projection** is a way of mapping the surface
of the earth (a curved 2D surface) onto a plane (a flat 2D surface). A
projection transforms a point on the earth (specified by latitude, longitude)
to a point on the **projection plane **.

In the Projection Manager, both the **projection** --
which kind of mapping to use -- and the
**area** of the Earth can be specified. You can make a Lambert
Conformal map of North America, and a Lambert Conformal map of
Sedgwick County, Kansas. Same projection, different areas.

The IDV provides four basic types of projections:
**Lambert Conformal**,
**Transverse Mercator**,
**Stereographic**, and
**Cylindrical Equidistant**
(the last is a special projection for datasets in **Lat/Lon**
coordinates which
deals with longitude wrapping around the cylinder).
Each of these can be parameterized (e.g., tangent point, origin longitude)
to create a specific projection area of that
type. When you define a projection and area, you specify the type
of projection and its parameters.

Projection Manager Window

You can bring up the Projection Manager
with the `Projections->New/Edit`

menu option. Projections supplied with the IDV are shown in the list.
There may be additional projections you have created and named.
In the figure, the IDV North American projection is highlighted,
and displayed on the left.
To modify or create a new projection: choose **Edit** or **New**
from the menu; the **Define/Edit Projection dialog box** appears (see
below).

The IDV starts with a default projection.
Use the **Default** pull-down menu to select the projection that
will be shown each time your IDV starts. (The default projection may
not be used
if you are starting the IDV with a
Bundle of
configuration information.)

You can also **Export** a projection to a file.

Define/Edit Projection Window

This allows you to define new projections, and
to modify existing ones. Remember that a Projection not only consists of
the mathematical projection, but also the area of the Earth that is seen.
Here is how to create a new or revised projection:

- Choose
**Edit**or**New**from Projection Manager Window. - Choose a projection Type from the pull-down menu
- Fill in the projection parameters
- Press
**Preview**to see what the Projection looks like - Set the map area shown with this named projection by zooming and panning the view on the left. To zoom, drag the left mouse button. Use the other buttons in the window to zoom out and move around.
- Give it a new or revised name if necessary (projection names are unique). Use ">" between names to create a category hierarchy.
- Press
**Save**to move the projection to the main projection manager.

In the example shown, a Lambert Conformal projection is being defined with the projection parameters as shown in the figure.

You can remove any projection from the main list by clicking on its
name to highlight it, and then clicking on the **Delete** button.