SHAPELY_BUFFER
Computes a buffer geometry around an input geometry from WKT using a specified buffer distance. Positive distance expands geometry and negative distance contracts it where possible.
Conceptually, the buffer is the Minkowski sum (or difference for negative distance) with a radius-d disk:
G \oplus B_d
The function returns an Excel data type with the buffered WKT as the primary value plus area and perimeter properties.
Excel Usage
=SHAPELY_BUFFER(geometry, distance, quad_segs)geometry(str, required): Input geometry (WKT).distance(float, required): The radius of the buffer.quad_segs(int, optional, default: 2): Number of segments used to approximate a quarter circle.
Returns (dict): Excel Entity representing the buffered geometry (Polygon).
Example 1: Buffer around a point
Inputs:
| geometry | distance | quad_segs |
|---|---|---|
| POINT (0 0) | 1 | 1 |
Excel formula:
=SHAPELY_BUFFER("POINT (0 0)", 1, 1)Expected output:
{"type":"String","basicValue":"POLYGON ((1 0, 0.0000000000000001 -1, -1 -0.0000000000000001, -0.0000000000000002 1, 1 0))","properties":{"Area":{"type":"Double","basicValue":2},"Perimeter":{"type":"Double","basicValue":5.65685},"WKT":{"type":"String","basicValue":"POLYGON ((1 0, 0.0000000000000001 -1, -1 -0.0000000000000001, -0.0000000000000002 1, 1 0))"}}}
Example 2: Buffer around a line
Inputs:
| geometry | distance | quad_segs |
|---|---|---|
| LINESTRING (0 0, 10 0) | 2 | 1 |
Excel formula:
=SHAPELY_BUFFER("LINESTRING (0 0, 10 0)", 2, 1)Expected output:
{"type":"String","basicValue":"POLYGON ((10 2, 12 0, 10 -2, 0 -2, -2 0.0000000000000002, 0 2, 10 2))","properties":{"Area":{"type":"Double","basicValue":48},"Perimeter":{"type":"Double","basicValue":31.3137},"WKT":{"type":"String","basicValue":"POLYGON ((10 2, 12 0, 10 -2, 0 -2, -2 0.0000000000000002, 0 2, 10 2))"}}}
Example 3: Buffer around a polygon
Inputs:
| geometry | distance | quad_segs |
|---|---|---|
| POLYGON ((0 0, 2 0, 2 2, 0 2, 0 0)) | 0.5 | 1 |
Excel formula:
=SHAPELY_BUFFER("POLYGON ((0 0, 2 0, 2 2, 0 2, 0 0))", 0.5, 1)Expected output:
{"type":"String","basicValue":"POLYGON ((-0.5 0, -0.5 2, 0 2.5, 2 2.5, 2.5 2, 2.5 0, 2 -0.5, 0 -0.5, -0.5 0))","properties":{"Area":{"type":"Double","basicValue":8.5},"Perimeter":{"type":"Double","basicValue":10.8284},"WKT":{"type":"String","basicValue":"POLYGON ((-0.5 0, -0.5 2, 0 2.5, 2 2.5, 2.5 2, 2.5 0, 2 -0.5, 0 -0.5, -0.5 0))"}}}
Example 4: Negative buffer on polygon
Inputs:
| geometry | distance |
|---|---|
| POLYGON ((0 0, 6 0, 6 6, 0 6, 0 0)) | -1 |
Excel formula:
=SHAPELY_BUFFER("POLYGON ((0 0, 6 0, 6 6, 0 6, 0 0))", -1)Expected output:
{"type":"String","basicValue":"POLYGON ((1 1, 1 5, 5 5, 5 1, 1 1))","properties":{"Area":{"type":"Double","basicValue":16},"Perimeter":{"type":"Double","basicValue":16},"WKT":{"type":"String","basicValue":"POLYGON ((1 1, 1 5, 5 5, 5 1, 1 1))"}}}
Python Code
from shapely import wkt
def shapely_buffer(geometry, distance, quad_segs=2):
"""
Returns a representation of all points within a given distance of the this geometric object.
See: https://shapely.readthedocs.io/en/stable/reference/shapely.buffer.html
This example function is provided as-is without any representation of accuracy.
Args:
geometry (str): Input geometry (WKT).
distance (float): The radius of the buffer.
quad_segs (int, optional): Number of segments used to approximate a quarter circle. Default is 2.
Returns:
dict: Excel Entity representing the buffered geometry (Polygon).
"""
try:
if not geometry:
return "Error: Geometry required"
geom = wkt.loads(geometry)
buffered = geom.buffer(distance, quad_segs=quad_segs)
wkt_str = buffered.wkt
return {
"type": "String",
"basicValue": wkt_str,
"properties": {
"Area": {"type": "Double", "basicValue": float(buffered.area)},
"Perimeter": {"type": "Double", "basicValue": float(buffered.length)},
"WKT": {"type": "String", "basicValue": wkt_str}
}
}
except Exception as e:
return f"Error: {str(e)}"