| iTool User's Guide: Working with Maps |

## Applying a Map Projection

A map projection establishes the axis type and coordinate conversion mechanism for mapping points on the earth's surface, expressed in latitude and longitude, to points on a plane, according to one of several possible map projections.

You can apply a map projection before or after you import image or contour data into the iMap tool. To do so, select Operations Map Projection. This command opens the Map Projection dialog, shown in Figure 15-1.

Figure 15-1: The Map Projection Dialog

Figure 15-1: The Map Projection Dialog

You can apply a map projection to another iTool as well. If you do, the tool will adapt to expose iMap functionality, including the iMap operations and the Map panel.

Table 15-1 shows the common projection properties.

Table 15-1: Common Map Projection Properties

Table 15-1: Common Map Projection Properties
Name | Description
--- | ---
Description | Description of the map projection
Show dialog | Show this dialog before executing the Map Projection operation
Projection | Name of the map projection
Ellipsoid (datum) | Semimajor and -minor axes that define the ellipsoid
Semimajor axis | Length of the semimajor axis, in meters, for the reference ellipsoid
Semiminor axis | Length of the semiminor axis, in meters, for the reference ellipsoid
Center longitude (degrees) | Longitude in degrees of the projection's center
Center latitude (degrees) | Latitude in degrees of the projection's center
Longitude minimum (deg) | Minimum longitude to include in the projection, in degrees
Longitude maximum (deg) | Maximum longitude to include in the projection, in degrees
Latitude minimum (deg) | Minimum latitude to include in the projection, in degrees
Latitude maximum (deg) | Maximum latitude to include in the projection, in degrees
False easting (meters) | False easting to be added to each x-coordinate, in meters
False northing (meters) | False northing to be added to each y-coordinate, in meters

In addition to these properties, the following properties (Table 15-2) become available depending on the selected projection:

Table 15-2: Properties for Selected Map Projections

Table 15-2: Properties for Selected Map Projections
Name | Description
--- | ---
Height (meters) | Height above surface, in meters, for satellite projections
Hemisphere | Hemisphere for UTM and Polar projections
HOM azimuth angle (deg) | Hotine Oblique Mercator azimuth angle (degrees) east
HOM latitude 1 (deg) | Hotine Oblique Mercator latitude, in degrees, of the first point
HOM latitude 2 (deg) | Hotine Oblique Mercator latitude, in degrees, of the second point
HOM longitude 1 (deg) | Hotine Oblique Mercator longitude, in degrees, of the first point
HOM longitude 2 (deg) | Hotine Oblique Mercator longitude, in degrees, of the second point
IS longitudinal zones | Intergerized Sinusoidal number of longitudinal zones
IS row justify flag | Integerized Sinusoidal flag that indicates what to do with rows with an odd number of columns. The following values are allowed: 0 — Indicates the extra column is on the right of the projection y-axis 1 — Indicates the extra column is on the left of the projection y-axis 2 — Calculates an even number of columns
Mercator scale | Scale factor at the central meridian (for the Transverse Mercator projection) or the center of the projection (for the Hotine Oblique Mercator projection)
NAD27 Zone name (FIPS) | NAD27 State Plane Coordinate System Zone (FIPSZone)
NAD83 Zone name (FIPS) | NAD83 State Plane Coordinate System Zone (FIPSZone)
OEA horizontal shape m | Oblated equal area horizontal (m) shape parameter
OEA vertical shape n | Oblated equal area vertical (n) shape parameter
OEA rotation angle (deg) | Oblated equal area rotation angle, in degrees
SOM end-of-path flag | Space Oblique Mercator Landsat end-of-path flag, where 0 is the start and 1 is the end
SOM inclination (deg) | Space Oblique Mercator orbit inclination angle, in degrees, of the ascending node, counter-clockwise from the equator
SOM Landsat number | Space Oblique Mercator Landsat number (Worldwide Reference System)
SOM Landsat path | Space Oblique Mercator Landsat path number
SOM longitude (deg) | Space Oblique Mercator longitude, in degrees, of the ascending node
SOM period (minutes) | Space Oblique Mercator satellite period, in minutes
SOM ratio | Space Oblique Mercator Landsat ratio that compensates for confusion at the northern end of orbit
Standard parallel 1 (deg) | First standard parallel (degrees latitude) of true scale
Standard parallel 2 (deg) | Second standard parallel (degrees latitude) of true scale
Zone (1-60) | Universal Transverse Mercator (UTM) grid zone number (must be negative for zones in the southern hemisphere)

Note The map projection properties are normally taken from the currently selected dataspace. However, in the Operations Browser, the map projection properties are registered on the operation itself. Changing these properties in the Operations Browser will have no affect on the currently selected dataspace. If the Show Dialog property is set to False and then the Map Projection operation is activated, the projection properties will be copied directly from the Map Projection operation onto the currently selected dataspace.

Note Each projection has default longitude and latitude limits. If you have not modified one of these limits (the longitude and latitude minimum and maximum properties), the Map Projection operation will automatically use its default limit. However, if you have modified one of these limits, the Map Projection operation will use either your desired limit or the default limit, whichever is smaller.

IDL Online Help (March 01, 2006)