GEMPAK Manual |
Programs | Parameters

PROJ PROJ is the map projection, projection angles, and margins separated by slashes and an optional image drop flag separated from the rest by a bar: map proj / ang1;ang2;ang3 / l;b;r;t (margins) | image drop flag For all map projections, the lower left and upper right corners of the graphics area should be specified in GAREA. The following simple map projections may be specified: MER Mercator NPS North Polar Stereographic SPS South Polar Stereographic LCC Northern Hemisphere Lambert Conic Conformal SCC Southern Hemisphere Lambert Conic Conformal CED Cylindrical Equidistant MCD Modified Cylindrical Equidistant NOR North Orthographic SOR South Orthographic The following full map projections may also be specified: MER (CYL) Mercator CED (CYL) Cylindrical Equidistant MCD (CYL) Modified Cylindrical Equidistant STR (AZM) Polar Stereographic AED (AZM) Azimuthal Equidistant ORT (AZM) Orthographic LEA (AZM) Lambert equal area GNO (AZM) Gnomonic LCC (CON) Northern Hemisphere Lambert Conic Conformal SCC (CON) Southern Hemisphere Lambert Conic Conformal In addition for full map projections, three angles MUST be specified in PROJ. The angles have the following meanings for the different projection classes: CYL angle1 -- latitude of origin on the projection cylinder 0 = Equator angle2 -- longitude of origin on the projection cylinder 0 = Greenwich meridian angle3 -- angle to skew the projection by rotation of the cylindrical surface of projection about the line from the Earth's center passing through the origin point. This results in curved latitude and longitude lines. If angle3 is greater than 360 or less than -360 degrees, then the rectangular Cartesian coordinate system on the projection plane is rotated +/- |angle3|-360 degrees. This results in latitude and longitude lines that are skewed with respect to the edge of the map. This option is only valid when specifying a map projection and is not available for grid projections. The difference between |angle3| < 360 and |angle3| > 360 is that, in the former case, the rotation is applied to the developable cylindrical surface before projection and subsequent development; while, in the latter case, the rotation is applied to the Cartesian coordinate system in the plane after development. Development here refers to the mathematical flattening of the surface of projection into a planar surface. Exception: MCD angle1 -- scaling factor for latitude 0 = default scaling (1/cos(avglat)) angle2 -- longitude of origin (center longitude) angle3 -- not used AZM angle1 -- latitude of the projection's point of tangency angle2 -- longitude of the projection's point of tangency angle3 -- angle to skew the projection by rotation about the line from the Earth's center passing through the point of tangency CON angle1 -- standard latitude 1 angle2 -- polon is the central longitude angle3 -- standard latitude 2 The angles for the full map projection types are given as three numbers separated with semicolons. Note that THREE angles must be entered even if some angles are not used. Note that transverse projections may be obtained using a cylindrical projection with the first angle set to either 90 or -90. The second angle is the longitude at which the cylinder axis intersects the equator. This will be the transformed location of the "south" pole when the first angle is 90 or the "north" pole when the first angle is -90. For example, if angle1 = 90 and angle2 = 0, the axis of the cylinder of projection is perpendicular to the earth's axis and enters the earth at 0N 0E and emerges at 0N 180E. The great circle formed by 90E and 90W becomes the "equator" on the cylinder. This cylinder is ideal for a transverse cylindrical projection of locations on the continent of North America. Satellite and radar projections are available: SAT specifies remapped or nonremapped satellite projections. RAD specifies the radar projection. Currently, the McIDAS area format is supported for satellite and radar images. NIDS radar images from WSI may also be displayed. The image drop flag may be specified as a D or an ND, and is valid for SAT and RAD only. A value of D causes the image to be dropped before any additional graphics are drawn. Conversely, a value of ND does not drop the image. When the image drop flag is undefined, the image is dropped when CLEAR is set to YES, and is not dropped when CLEAR is set to NO. If the projection is DEF or is blank, a default projection will be obtained from the geographic table for the specified GAREA. If no default projection has been defined for the specified GAREA and the projection is DEF, the current map projection will be used. In the grid programs the following graph projections are also available: LIN linear x, linear y LOG linear x, logarithmic y KAP linear x, y ** KAPPA POL polar coordinates ( R, THETA ) Margins may be input as four numbers separated with semicolons. The four numbers represent the left, bottom, right, and top margin sizes in character widths. If no margins are specified, the default will be (0,3,0,0) in map mode and (6,4,4,1) in graph mode. If the input for the margins is NM, all four margins will be set to 0.