The GREMOVE Procedure

PROC GREMOVE Statement

Identifies the input and output map data sets.

Requirements:

An input map data set is required.

Syntax

PROC GREMOVE <DATA=input-map-data-set>
<FUZZ=fuzz-factor>
<OUT=output-map-data-set>
<NODECYCLE>;

Options

DATA=input-map-data-set

specifies the map data set that is to be processed. By default, the procedure uses the most recently created SAS data set. The GREMOVE procedure expects the observations in the input map data set to be sorted in ascending order of the BY-variable values.

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Creating an Outline Map of Africa.

FUZZ=fuzz-factor

specifies a tolerance for possible error in the data. This allows for points that are very close but not quite equal to be considered as the same point. The fuzz-factor can be any non-negative number. A fuzz-factor of 0.0 would indicate that the points have to be exactly the same. The unit represented by the fuzz-factor (degrees, radians, feet, meters, kilometers, miles) is the same as that represented by the X and Y values of the points.

The error is computed the same in both X and Y directions using the following formula:

Point_is_equal = (ABS(x1 - x2) <= fuzz-factor) && (ABS(y1 - y2) <= fuzz-factor)

NODECYCLE | NC

tells PROC GREMOVE to use a topological algorithm for closing the resulting polygons. By default, PROC GREMOVE simply removes internal boundaries without using any polygon information. This might cause errors in closing the resulting polygons in certain cases--specifically when two resulting polygons intersect at a single point. Using a topological algorithm allows PROC GREMOVE to traverse the resulting polygons for proper closure of the polygons. When the single point intersection is encountered, the algorithm uses the topology to correctly interpret which existing segment to choose in closing the polygon. The use of NODECYCLE, thus, requires that the data be topologically correct (that is, polygons do not overlap themselves or each other and there are no anomalies in the boundaries such as a repeated series of points).

Certain SAS/GRAPH procedures, such as PROC GREDUCE, which have no knowledge of topology and do not maintain topology, can produce topologically incorrect polygons. Therefore, it is recommended that you not use PROC GREDUCE if you are going to use PROC GREMOVE with NODECYCLE specified.

OUT=output-data-set

names the new map data set, which contains the coordinates of the new unit areas created by the GREMOVE procedure. By default, the GREMOVE procedure names the new data set using 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.