> library(stppSim)
> load(file = system.file("extdata", "camden.rda",
+ package="stppSim"))
> boundary = camden$boundary 
> landuse <- camden$landuse
> spo <- artif_spo(poly = boundary, n_origin = 50, restriction_feat = landuse, n_foci=5, foci_separation = 0, mfocal = NULL, conc_type = "dispersed", p_ratio=20)
Error in h(simpleError(msg, call)) : 
  error in evaluating the argument 'obj' in selecting a method for function 'bbox': assignment of an object of class "character" is not valid for slot 'proj4string' in an object of class "Spatial"; is(value, "CRS") is not TRUE
> traceback()
18: h(simpleError(msg, call))
17: .handleSimpleError(function (cond) 
    .Internal(C_tryCatchHelper(addr, 1L, cond)), "assignment of an object of class \"character\" is not valid for slot 'proj4string' in an object of class \"Spatial\"; is(value, \"CRS\") is not TRUE", 
        base::quote(checkSlotAssignment(object, name, value)))
16: stop(gettextf("assignment of an object of class %s is not valid for slot %s in an object of class %s; is(value, \"%s\") is not TRUE", 
        dQuote(valueClass), sQuote(name), dQuote(cl), slotClass), 
        domain = NA)
15: checkSlotAssignment(object, name, value)
14: `slot<-`(`*tmp*`, what, value = "PROJCRS[\"OSGB 1936 / British National Grid\",\n    BASEGEOGCRS[\"OSGB 1936\",\n        DATUM[\"OSGB 1936\",\n            ELLIPSOID[\"Airy 1830\",6377563.396,299.3249646,\n                LENGTHUNIT[\"metre\",1]]],\n        PRIMEM[\"Greenwich\",0,\n            ANGLEUNIT[\"degree\",0.0174532925199433]],\n        ID[\"EPSG\",4277]],\n    CONVERSION[\"British National Grid\",\n        METHOD[\"Transverse Mercator\",\n            ID[\"EPSG\",9807]],\n        PARAMETER[\"Latitude of natural origin\",49,\n            ANGLEUNIT[\"degree\",0.0174532925199433],\n            ID[\"EPSG\",8801]],\n        PARAMETER[\"Longitude of natural origin\",-2,\n            ANGLEUNIT[\"degree\",0.0174532925199433],\n            ID[\"EPSG\",8802]],\n        PARAMETER[\"Scale factor at natural origin\",0.9996012717,\n            SCALEUNIT[\"unity\",1],\n            ID[\"EPSG\",8805]],\n        PARAMETER[\"False easting\",400000,\n            LENGTHUNIT[\"metre\",1],\n            ID[\"EPSG\",8806]],\n        PARAMETER[\"False northing\",-100000,\n            LENGTHUNIT[\"metre\",1],\n            ID[\"EPSG\",8807]]],\n    CS[Cartesian,2],\n        AXIS[\"(E)\",east,\n            ORDER[1],\n            LENGTHUNIT[\"metre\",1]],\n        AXIS[\"(N)\",north,\n            ORDER[2],\n            LENGTHUNIT[\"metre\",1]],\n    USAGE[\n        SCOPE[\"Engineering survey, topographic mapping.\"],\n        AREA[\"United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland). Isle of Man onshore.\"],\n        BBOX[49.75,-9,61.01,2.01]],\n    ID[\"EPSG\",27700]]")
13: asMethod(object)
12: as(object, superClass)
11: bbox(object)
10: validityMethod(as(object, superClass))
9: isTRUE(x)
8: anyStrings(validityMethod(as(object, superClass)))
7: validObject(.Object)
6: initialize(value, ...)
5: initialize(value, ...)
4: new("SpatialPoints", coords = coords, bbox = bbox, proj4string = proj4string)
3: SpatialPoints(cbind(ran_points$x, ran_points$y), proj4string = raster::crs(restriction_feat))
2: st_as_sf(SpatialPoints(cbind(ran_points$x, ran_points$y), proj4string = raster::crs(restriction_feat)))
1: artif_spo(poly = boundary, n_origin = 50, restriction_feat = landuse, 
       n_foci = 5, foci_separation = 0, mfocal = NULL, conc_type = "dispersed", 
       p_ratio = 20)