[R-sig-Geo] Reverse y-axis with geom_sf

[Kent Johnson]

Hi,

I am working with data representing cells in a tissue sample with lines and
polygonal regions defined in the same space. The cells and polygons are
represented and manipulated as simple features objects and visualized using
ggplot2 and geom_sf. Mostly this works very well. The problem is that the
coordinate system of my data has the origin at the top left corner. For
data with no CRS, geom_sf puts the origin at the bottom left so all my
plots are inverted.

Is there a way to invert the y axis while staying within sf (or possibly
sp?) The only answers I have found involve extracting the coordinates from
the sf objects and inverting or plotting from the raw data. Maybe by
creating a CRS with the correct orientation?

For a very simple example with just a few vectors - the code below plots an
arrow pointing down; I would like to invert the y-axis so it points up.
library(sf)
library(ggplot2)
s1 <- rbind(c(9, 11), c(10, 10))
s2 <- rbind(c(11, 11), c(10, 10))
s3 <- rbind(c(10,14), c(10, 12), c(10,10))
mls <- st_multilinestring(list(s1,s2,s3))

ggplot(mls) + geom_sf()

Thank you for any help,
Kent Johnson

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