How does the R package `terra` determine the number of dimensions of a raster projected without a template?

Question

I'd like to know how terra determines the number of rows and columns in a raster that is projected without a template raster. For example:

library(terra)

from <- rast()
mollweide <- 'PROJCRS[\"Sphere_Mollweide\",\n    BASEGEOGCRS[\"Unknown datum based upon the Authalic Sphere\",\n        DATUM[\"Not specified (based on Authalic Sphere)\",\n            ELLIPSOID[\"Sphere\",6371000,0,\n                LENGTHUNIT[\"metre\",1]]],\n        PRIMEM[\"Greenwich\",0,\n            ANGLEUNIT[\"Degree\",0.0174532925199433]]],\n    CONVERSION[\"Sphere_Mollweide\",\n        METHOD[\"Mollweide\"],\n        PARAMETER[\"Longitude of natural origin\",0,\n            ANGLEUNIT[\"Degree\",0.0174532925199433],\n            ID[\"EPSG\",8802]],\n        PARAMETER[\"False easting\",0,\n            LENGTHUNIT[\"metre\",1],\n            ID[\"EPSG\",8806]],\n        PARAMETER[\"False northing\",0,\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[\"Not known.\"],\n        AREA[\"World.\"],\n        BBOX[-90,-180,90,180]],\n    ID[\"ESRI\",53009]]'

to <- project(from, mollweide)

dim(from)
dim(to)

Inferring from the help for project(), it seems terra is using gdalwarp unless the user disables it, but the help page for gdalwarp does not elucidate.

Answer 1

The output raster geometry is chosen such that the extent and resolution closely match the input raster.