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The GPROJECT Procedure

PROC GPROJECT Statement

Identifies the input and output map data sets. Optionally specifies the type of projection, and criteria for clipping and projection.

Requirements: An input map data set is required.


Syntax

PROC GPROJECT <option(s)>;

option(s) can be one or more options from any or all of the following categories:

Options

ASIS
DUPOK
specify that observations for which the projected values for the X and Y variables are identical to those in the previous observation should be retained. By default, successive identical observations are deleted.

DATA=input-map-data-set
identifies the map data set to be processed. By default, the procedure uses the most recently created SAS data set.
See also: About the Input Map Data Set SAS Data Sets
Featured in: Projecting an Annotate Data Set

DEGREE
DEG
specifies that the units for the longitude (X variable) and latitude (Y variable) coordinates are degrees of arc. By default, coordinate units are considered to be radians.

EASTLONG
EAST
specifies that the longitude (X variable) values in the input map data set increase to the east. By default, longitude values increase to the west.

LATMAX=max-latitude
specify the maximum latitude that will be included in the projection. Any unit areas that cross the selected latitude are clipped and closed along the specified parallels. The LATMAX= and LATMIN= options do not have to be paired; you can specify a maximum latitude without specifying a minimum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, PROC GPROJECT treats the value of max-latitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.
Featured in: Clipping an Area from the Map

LATMIN=min-latitude
specify the minimum latitude that will be included in the projection. Any unit areas that cross the selected latitude are clipped and closed along the specified parallels. The LATMAX= and LATMIN= options do not have to be paired; you can specify a minimum latitude without specifying a maximum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, PROC GPROJECT treats the value of min-latitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.
Featured in: Clipping an Area from the Map

LONGMAX=max-longitude
specify the maximum longitude to be included in the projection. Any unit areas that cross the selected longitude are clipped and closed along the specified meridians. The LATMAX= and LATMIN= options do not have to be paired; you can specify a maximum longitude without specifying a minimum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, PROC GPROJECT treats the value of max-longitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.
Featured in: Clipping an Area from the Map

LONGMIN=min-longitude
specify the minimum longitude to be included in the projection. Any unit areas that cross the selected longitude are clipped and closed along the specified meridians. The LATMAX= and LATMIN= options do not have to be paired; you can specify a minimum longitude without specifying a maximum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, the GPROJECT procedure treats the value of min-longitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.
Featured in: Clipping an Area from the Map

OUT=output-map-data-set
names the new map data set, which contains the coordinates of the new unit areas that are created by the GPROJECT procedure.

By default, the GPROJECT procedure names the new data set that uses the DATAn naming convention. That is, the procedure uses the name WORK.DATAn, where n is the next unused number in sequence. Thus, the first automatically named data set is DATA1, the second is DATA2, and so on.
Featured in: Projecting an Annotate Data Set

PARADIV=n
specifies the divisor that computes the values used for standard parallels for the Albers' or Lambert's projections when explicit values are not provided. By default PARADIV=4, which causes standard parallels to be set at 1/4 and 3/4 of the range of latitude values in the input map data set.
See also: the PARALEL1= and PARALEL2= options

PARALEL1=latitude
PARALEL2=latitude
specify values for the standard parallels that are used in the Albers' or Lambert's projection. Latitude must be in degrees. Positive values indicate north of the equator, and negative values indicate south of the equator. These options are ignored for the gnomonic projection.

By default, the GPROJECT procedure calculates values for the standard parallels. The defaults are chosen to minimize the distortion inherent in the projection process. The algorithm used is

PARALEL1 = minlat + R / PD

PARALEL2 = maxlat - R / PD

where:

R
is the range of latitude values in the input map data set.

PD
is the PARADIV= value (see the discussion of the PARADIV=option).

minlat
is the minimum latitude value in the input map data set.

maxlat
is the maximum latitude value in the input map data set.

If you do not use PARALEL1= or PARALEL2=, or you omit either option, the GPROJECT procedure uses the calculated value for the missing parameter.

The standard parallels, whether explicitly specified or supplied by the procedure, must lie on the same side of the equator. If they do not, PROC GPROJECT prints an error message and stops (the procedure may calculate standard parallels that lie on opposite sides of the equator). When projecting a map data set that contains unit areas that cross the equator, you may have to explicitly specify standard parallels that both lie on the same side of the equatMor. If this causes excessive distortion of the map, you may be able to use the gnomonic projection instead of the Albers' or Lambert's projection because the gnomonic technique has no such limitations at the equator.

POLELAT=latitude
POLELONG=longitude
specify a projection pole to use for the gnomonic projection. The projection pole is the point at which the surface of the sphere touches the surface of the imaginary plane onto which the map is projected. POLELAT= specifies the latitude of the projection point.

Units for latitude are degrees; positive values indicate north of the equator, and negative values indicate south of the equator. POLELONG= gives the longitude for the projection point. Units for longitude are degrees; positive values indicate west of the prime meridian, and negative values indicate east of the prime meridian (unless EASTLONG also has been used in the PROC GPROJECT statement).

If you do not use POLELAT= or POLELONG=, or you omit either option, PROC GPROJECT uses values for the position of the center of the unit areas that are defined by the DATA= data set for the missing parameter.

Note:   The map that is defined by the input map data set should not contain points more than 85 degrees (1.48353 radians) from the projection pole; all points that exceed this value are deleted from the output map data set.  [cautionend]
Featured in: Emphasizing Map Areas

PROJECT=ALBERS | LAMBERT | GNOMON | NONE
specifies the projection method to apply to the map data set. Values for PROJECT= are as follows:

ALBERS
specifies Albers' equal-area projection with two standard parallels.

LAMBERT
specifies Lambert's conformal projection with two standard parallels.

GNOMON
specifies the gnomonic projection, which is an azimuthal projection.

NONE
specifies that no projection should be performed. Use this option in conjunction with the LATMIN=, LATMAX=, LONGMIN=, and LONGMAX= options to perform clipping without projection (for example, on map data sets that have already been projected).

By default, PROJECT=ALBERS.
See also: About Types of Map Projections
Featured in: Emphasizing Map Areas


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Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.