Dear Xiang,
I've not had a chance to try your code, but your example probably won't
work with the CRS set to WGS84. The buffer will use the units of the
coordinate system, so degrees, which will be far too large for the
bristol_zones example.
Assuming bristol_zones are in the UK, you need to reproject to BNG - 27700.
Also I am not sure whether bristol_zones from spDataLarge are in sp or
sf format.
Once those are addressed - I see no reason why the example in the Stack
Exchange should work.
Best wishes,
Nick.
On 19/02/2024 10:04, Xiang Ye via R-sig-Geo wrote:
Dear community,
I am learning some basic geometry operation functions of sf package including
st_buffer().
It seems there should be no wonder if I provide a negative value to the dist
argument in st_buffer(), I should expect an inward/shrinking buffer zone (I
also followed here:
https://gis.stackexchange.com/questions/392505/can-i-use-r-to-do-a-buffer-inside-polygons-shrink-polygons-negative-buffer).
However, it turn out to be as long as I provide a negative value, the output
will be an empty geometry:
library(sf)
library(spDataLarge)
st_geometry(bristol_zones[1, ]) -> a # a is the exemplary data set
a
Geometry set for 1 feature
Geometry type: MULTIPOLYGON
Dimension: XY
Bounding box: xmin: -2.534502 ymin: 51.40487 xmax: -2.488435 ymax: 51.43478
Geodetic CRS: WGS 84
MULTIPOLYGON (((-2.510462 51.42878, -2.507985 5...
st_buffer(a, 100)
Geometry set for 1 feature
Geometry type: POLYGON
Dimension: XY
Bounding box: xmin: -2.536248 ymin: 51.40393 xmax: -2.486907 ymax: 51.43598
Geodetic CRS: WGS 84
POLYGON ((-2.517834 51.43188, -2.518218 51.4318...
st_buffer(a, -100)
Geometry set for 1 feature (with 1 geometry empty)
Geometry type: POLYGON
Dimension: XY
Bounding box: xmin: NA ymin: NA xmax: NA ymax: NA
Geodetic CRS: WGS 84
POLYGON EMPTY
So I would like to know if it is possible to create inward buffer zones with
st_buffer()? If st_buffer() is not designed to perform this, what is the best
alternative?
Thank you, and have a great start of the week!
$B3pfF(B YE, Xiang
THINKING SPATIALLY<http://www.linkedin.com/in/spatialyexiang>.
Ph.D. in Spatial Statistics
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