Hi Sourav,
Perhaps replacing "+proj=aeqd +lat_0=cities [i,3][[1]]
+lon_0=cities[i,2][[1]] + x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m
+no_defs"
by
sprintf("+proj=aeqd +lat_0=%f
+lon_0=%f + x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m
+no_defs", cities [i,3][[1]], cities[i,2][[1]])
etc.
could solve your problem.
HTH
Zivan
Le sam. 4 juil. 2020 ? 10:07, Sourav Sarkar <sourav.sarkar at ahduni.edu.in>
a ?crit :
Hi All,
I have a sf dataframe (cities) of point locations of about a hundred
cities
in India with latitudes in the second column and longitudes in the third
column. I am trying to create a geodesic buffer around each of these
points
by projecting them to azimuthal equidistant projection centred at the
respective point and then using the st_buffer function.
The error is occuring when I try to centre the equidistant projection to
my
preferred latitude and longitude since lat_0 and lon_0 accept only numbers
which I do not want to put manually. From searches over the internet, it
seems to me that probably something related to paste or \"" needs to be
applied but since I am not an expert I am unable to get the correct code.
My code looks something like this:
a <-st_transform(cities[i,], "+proj=aeqd +lat_0=cities [i,3][[1]]
+lon_0=cities[i,2][[1]] + x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m
+no_defs")
buffer_aeqd =st_transform(cities[1,], "+proj=aeqd +lat_0= cities[1,3][[1]]
+lon_0= cities[1,2][[1]] + x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m
+no_defs")
buffer_aeqd=st_buffer(buffer_aeqd, 50000)
buffer_aeqd=st_transform(buffer_aeqd, 4326)
for (i in 2:nrow(cities)){
a = st_transform(cities[i,], "+proj=aeqd +lat_0=cities [i,3][[1]]
+lon_0=cities[i,2][[1]] + x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m
+no_defs")
a=st_buffer(a, 200000)
a=st_transform(a, 4326)
buffer_aeqd=rbind(buffer_aeqd, a)
}
remove(a)
It will be very nice if you can give me some leads. Thank You very much in
advance.
Yours sincerely,
--
Sourav Sarkar,
Assistant Professor,
School of Arts and Sciences,
Ahmedabad University
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