| iTool User's Guide: Working with Maps |

## Registering an Image

The Map Register Image wizard, shown in Figure 15-3, registers an image's data, creating a correspondence between the image pixels and points on the earth's surface. This registration step is necessary to let the iMap tool properly display the image data in the map projection you select.

The wizard launches automatically when you import image data or open an image file for which not all necessary map information is known. To launch the wizard after the image is open and registered (e.g., if you want to change the registering properties), select Operations Map Register Image.

Figure 15-3: The Map Register Image Wizard — Step 1

Figure 15-3: The Map Register Image Wizard — Step 1

The coordinates are in either meters or degrees; which units you choose for the translation can affect how the image appears in a map projection. Selecting meters means that the image data have already been warped to a particular projection, and you need to tell IDL which projection to use in displaying the image. Selecting degrees, on the other hand, means that the image data are not already warped, so you do not need to specify a map projection for the image. It is important that you know in which units your data are, to make the correct decision when registering the image for display.

The Map Register Image wizard reflects this difference between the units by having three steps for meters and two for degrees:

1. Select the coordinate units.

2. Set the pixel minimum, maximum, and size values.

3. (Meters only) Specify the map projection to associate with the image and, if desired, with the dataspace as well.

Once you have set these registering properties and map projection (if applicable), IDL registers the image data, and the iMap tool displays the image and the Image panel along with the Map panel.

Note If the image being registered was originally from either a TIFF file containing GeoTIFF tags or a JPEG2000 file containing a GeoTIFF UUID box, an additional button, Show GeoTIFF tags, is available on the latter dialogs of the Map Register Image wizard (Steps 2 and 3 for meters, Step 2 for degrees). Pressing this button brings up a separate text window containing the GeoTIFF tags, which can be useful in determining the map registration properties. For a list of GeoTIFF tags, see the GEOTIFF keyword in READ_TIFF. For more information on JPEG2000 with GeoTIFF, see http://www.remotesensing.org/jpeg2000/.

The rest of this section describes the two registration pathways, with meters or with degrees, in more detail.

### Registering an Image in Meters

If you select Meters as the coordinate units in Step 1 and click on Next, you see the wizard's Step 2 dialog for meters, shown in Figure 15-4.

Figure 15-4: The Map Register Image Wizard — Step 2 (Meters)

Figure 15-4: The Map Register Image Wizard — Step 2 (Meters)

Table 15-4 shows the properties associated with meter coordinates.

Table 15-4: Meter Coordinate Properties

Table 15-4: Meter Coordinate Properties
Name | Description
--- | ---
X (or U) minimum (meters) | Minimum position in the x (or u) direction, in meters, of the image data
X (or U) maximum (meters) | Maximum position in the x (or u) direction, in meters, of the image data
X (or U) pixel size (meters) | Pixel size, in meters, in the x (or u) direction
Y (or V) minimum (meters) | Minimum position in the y (or v) direction, in meters, of the image data
Y (or V) maximum (meters) | Maximum position in the y (or v) direction, in meters, of the image data
Y (or V) pixel size (meters) | Pixel size, in meters, in the y (or v) direction

Note The (u.v) coordinates refer to the UV plane of a cylindrical projection.

Entering the minimum value and the pixel size automatically updates the maximum value.

Figure 15-5 shows the final step in the Map Register Image wizard for the Meters option.

Figure 15-5: The Map Register Image Wizard: Step 3 (Meters)

Figure 15-5: The Map Register Image Wizard: Step 3 (Meters)

In this step, you can select a map projection to associate with the image. You also have the option of updating the dataspace map projection to use this projection.

### Registering an Image in Degrees

If you select Degrees as the coordinate units in Step 1 and click on Next, you see the wizard's Step 2 dialog for degrees, shown in Figure 15-6.

Figure 15-6: The Map Register Image Wizard: Step 2 (Degrees)

Figure 15-6: The Map Register Image Wizard: Step 2 (Degrees)

Table 15-5 shows the properties associated with degree coordinates.

Table 15-5: Degree Coordinate Properties

Table 15-5: Degree Coordinate Properties
Name | Description
--- | ---
Longitude minimum (deg) | Minimum longitude position, in degrees, of the image data
Longitude maximum (deg) | Maximum longitude position, in degrees, of the image data
Longitude pixel size (deg) | Pixel size, in degrees, in the longitude direction
Latitude minimum (deg) | Minimum latitude position, in degrees, of the image data
Latitude maximum (deg) | Maximum latitude position, in degrees, of the image data
Latitude pixel size (deg) | Pixel size, in degrees, in the latitude direction

Entering the minimum value and the pixel size automatically updates the maximum value.

IDL Online Help (March 01, 2006)