topojson_json with sf classes may not be working

[sckott]

Just noticed this cause I was going to reply to this old SO thread https://gis.stackexchange.com/questions/250760/convert-sf-or-geojson-to-topojson-in-r-geojsonio

Seems like topojson_json() is behaving badly for sf inputs, e.g.:

p1 <- rbind(c(0,0), c(1,0), c(3,2), c(2,4), c(1,4), c(0,0))
poly <- rbind(c(1,1), c(1,2), c(2,2), c(1,1))
poly_sfg <-st_polygon(list(p1))
topojson_json(poly_sfg)
#> {"type":"Topology","objects":{"foo":{"type":"GeometryCollection","geometries":[{"type":null}]}},"arcs":[]}

it's empty, whereas it should not be.

if we do this it works

topojson_json(poly_sfg, type = "auto")
#> {"type":"Topology","objects":{"foo":{"type":"Polygon","arcs":[[0]]}},"arcs":[[[0,0],[1,0],[3,2],[2,4],[1,4],[0,0]]],"bbox":[0,0,3,4]}

but not sure if that's the desired output? Doing type="auto" makes the other examples work as well

@ateucher ?

[sckott]

@ateucher does this approach seem reasonable? on branch https://github.com/ropensci/geojsonio/compare/topojson_json-auto-sf

Changed topojson_json to change type to auto if a sf class detected. and otherwise leave type as is.

library(geojsonio)
library(sf)
p1 <- rbind(c(0,0), c(1,0), c(3,2), c(2,4), c(1,4), c(0,0))
poly <- rbind(c(1,1), c(1,2), c(2,2), c(1,1))
poly_sfg <- st_polygon(list(p1))
topojson_json(poly_sfg)
#> sf/sfc/sfg class detected; using type="auto"
#> {"type":"Topology","objects":{"foo":{"type":"Polygon","arcs":[[0]]}},"arcs":[[[0,0],[1,0],[3,2],[2,4],[1,4],[0,0]]],"bbox":[0,0,3,4]}

topojson_list(poly_sfg)
#> sf/sfc/sfg class detected; using type="auto"
#> $type
#> [1] "Topology"
#> 
#> $objects
#> $objects$foo
#> $objects$foo$type
#> [1] "Polygon"
#> 
#> $objects$foo$arcs
#> $objects$foo$arcs[[1]]
#> [1] 0
#> 
#> 
#> 
#> 
#> $arcs
#> $arcs[[1]]
#> $arcs[[1]][[1]]
#> [1] 0 0
#> 
#> $arcs[[1]][[2]]
#> [1] 1 0
#> 
#> $arcs[[1]][[3]]
#> [1] 3 2
#> 
#> $arcs[[1]][[4]]
#> [1] 2 4
#> 
#> $arcs[[1]][[5]]
#> [1] 1 4
#> 
#> $arcs[[1]][[6]]
#> [1] 0 0
#> 
#> 
#> 
#> $bbox
#> [1] 0 0 3 4

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