GREMOVE Procedure
PROC GREMOVE Statement
Identifies the input and output map data sets.
Requirement: |
An input map data set is required. |
Syntax
PROC GREMOVE <DATA=input-map-data-set>
<FUZZ=fuzz-factor>
<OUT=output-map-data-set>
<NODECYCLE>;
Summary of Optional Arguments
specifies the map data set that is to be processed.
specifies a tolerance for possible error in the
data.
tells PROC GREMOVE to use a topological algorithm
for closing the resulting polygons.
names the new map data set, which contains the coordinates
of the new unit areas created by the GREMOVE procedure.
Optional Arguments
- 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.
- 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 nonnegative 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.
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