Dear Xiang,
sure it is possible. I suggest using a CRS that is projected, e.g. 3857
(Web Mercator), or turn off s2 geometry. If you turn off s2, then
st_buffer() will interpret the dist parameter in degrees. Anyway, if you
choose a small enough number, then you'll get a non-empty geometry.
> sf_use_s2(FALSE)
Spherical geometry (s2) switched off
> st_buffer(a, -100)
dist is assumed to be in decimal degrees (arc_degrees).
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
Warning message:
In st_buffer.sfc(a, -100) :
st_buffer does not correctly buffer longitude/latitude data
> st_buffer(a, -0.001)
dist is assumed to be in decimal degrees (arc_degrees).
Geometry set for 1 feature
Geometry type: POLYGON
Dimension: XY
Bounding box: xmin: -2.533411 ymin: 51.40595 xmax: -2.489763 ymax: 51.4315
Geodetic CRS: WGS 84
POLYGON ((-2.533083 51.41747, -2.528692 51.4204...
Warning message:
In st_buffer.sfc(a, -0.001) :
st_buffer does not correctly buffer longitude/latitude data
(I don't know why s2 can't deal with negative distance if the CRS is
WGS-84.)
HTH,
Ákos
____________
Ákos Bede-Fazekas
Centre for Ecological Research, Hungary
2024. 02. 19. 11:04 keltezéssel, Xiang Ye via R-sig-Geo írta:
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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