R Shiny Leaflet: Plot from shape file SF object WGS 84 missing lng ang lat data

Question

First time working with shape files and new to mapping so please forgive my potential ignorance here. Also, I am unable to create MWE due to access to shape file in question.

I am creating a leaflet map within Shiny and using the SF package for reading shape files. I am trying to import a shape file to display as a map overlay.

Shape file:

Simple feature collection with 13 features and 20 fields
Geometry type: MULTIPOLYGON
Dimension:     XYZ
Bounding box:  xmin: 389792.7 ymin: 2295313 xmax: 431035.9 ymax: 2376519
z_range:       zmin: 0 zmax: 0
Projected CRS: WGS 84 / UTM zone 46N

Structure:

Classes ‘sf’ and 'data.frame':  13 obs. of  21 variables:
 $ Join_Count: num  0 0 0 0 0 0 0 0 0 0 ...
 $ TARGET_FID: num  0 0 0 0 0 0 0 0 0 0 ...
 $ JOIN_FID  : num  0 0 0 0 0 0 0 0 0 0 ...
 $ Id        : num  0 0 0 0 0 0 0 0 0 0 ...
 $ OBJECTID  : num  0 0 0 0 0 0 0 0 0 0 ...
 $ Name      : chr  "Teknaf Beach Deposits" "Tipam" "Girujan Clay" "Upper Bokabil sst-shl alteration" ...
 $ FolderPath: chr  NA "Geology_Interpretation.kmz/Geology_Interpretation" "Geology_Interpretation.kmz/Geology_Interpretation" "Geology_Interpretation.kmz/Geology_Interpretation" ...
 $ SymbolID  : num  0 0 1 2 4 5 6 5 5 6 ...
 $ AltMode   : num  0 0 0 0 0 0 0 0 0 0 ...
 $ Base      : num  0 0 0 0 0 0 0 0 0 0 ...
 $ Clamped   : num  0 -1 -1 -1 -1 -1 -1 -1 -1 -1 ...
 $ Extruded  : num  0 0 0 0 0 0 0 0 0 0 ...
 $ Snippet   : chr  NA NA NA NA ...
 $ PopupInfo : chr  NA NA NA NA ...
 $ Shape_Leng: num  0 2.485 1.368 0.163 0.157 ...
 $ Shape_Le_1: num  0 2.493 1.426 0.892 0.812 ...
 $ Shape_Area: num  0 0.04115 0.00439 0.00418 0.00205 ...
 $ OBJECTID_1: num  0 1 2 3 5 9 11 12 14 15 ...
 $ layer     : chr  NA "Clip_all" "Clip_all" "Clip_all" ...
 $ path      : chr  NA "MultiPolygonZ?crs=EPSG:3857&field=OBJECTID_1:long(10,0)&field=Name:string(254,0)&field=FolderPath:string(254,0)"| __truncated__ "MultiPolygonZ?crs=EPSG:3857&field=OBJECTID_1:long(10,0)&field=Name:string(254,0)&field=FolderPath:string(254,0)"| __truncated__ "MultiPolygonZ?crs=EPSG:3857&field=OBJECTID_1:long(10,0)&field=Name:string(254,0)&field=FolderPath:string(254,0)"| __truncated__ ...
 $ geometry  :sfc_MULTIPOLYGON of length 13; first list element: List of 1
  ..$ :List of 1
  .. ..$ : num [1:832, 1:3] 424728 424746 424763 424781 424799 ...
  ..- attr(*, "class")= chr [1:3] "XYZ" "MULTIPOLYGON" "sfg"
 - attr(*, "sf_column")= chr "geometry"
 - attr(*, "agr")= Factor w/ 3 levels "constant","aggregate",..: NA NA NA NA NA NA NA NA NA NA ...
  ..- attr(*, "names")= chr [1:20] "Join_Count" "TARGET_FID" "JOIN_FID" "Id" ...

Previous shapes have been simply added using addPolygons and function perfectly. However, I am unable to map this particular file which I assume stems from two things. 1) There are no lng or lat data stored as far as I can see. 2) The file uses WGS 84 CRS whereas leaflet needs ESRI 3857?

I've attempted to transform the shapefile using shape <- shape %>% st_transform(3857) but receive the following: addPolygons must be called with both lng and lat, or with neither. So I guess this confirms that the missing lng and lat data are the issue here?

My question is, is there anything I can do to resolve this or is there a more fundamental issue with the creation of the shape file itself?

Advice appreciated!

Answer 1

Your object is in a projected CRS (see the last line of your first printout). Specifically it seems to be in https://epsg.io/32646

To make it work with leaflet consider transforming (= sf::st_transform()) it to unprojected CRS - "pure" WGS 84 = EPSG::4326 should be good.

Also make double certain that you are adding your object via the data argument of leaflet::addPolygons() - and not via the first (or technically the second, since we are in a pipe) argument, which is not data but lng - thus causing your polygons object to have "defined" longitude (wrongly, but I digress) but no latitude. This is the most common root cause of the error you mention.