[R-sig-Geo] rast() in terra doesn't show cell values

[Noah Charney]

Thanks!  That fixed it!
-Noah

On Wed, Mar 8, 2023 at 5:40 PM Sarah Goslee <sarah.goslee using gmail.com> wrote:

> Hi Noah,
>
> It appears to be the same problem as this: [reading rasters in r using
> terra package](
> https://gis.stackexchange.com/questions/398061/reading-rasters-in-r-using-terra-package
> ).
> As in that question, adding 0 forces the conversion, but loses all the
> information about color table, etc.
>
> canopy <- rast('nlcd_2016_treecanopy_2019_08_31.img', lyrs=1)
>
> c2 <- canopy + 0
>
> > c2
> class       : SpatRaster
> dimensions  : 104424, 161190, 1  (nrow, ncol, nlyr)
> resolution  : 30, 30  (x, y)
> extent      : -2493045, 2342655, 177285, 3310005  (xmin, xmax, ymin, ymax)
> coord. ref. : Albers Conical Equal Area
> source      : spat_t0Rj6gEgi2CzsAZ_16778.tif
> name        : Histogram
> min value   :         0
> max value   :       255
>
> I didn't try the devel version of terra, though.
>
> Sarah
>
> On Wed, Mar 8, 2023 at 6:17 AM Noah Charney <noah.charney using maine.edu>
> wrote:
> >
> > Hi,
> > Can someone tell me what I'm missing?  I can't get the rast() function in
> > terra to return the actual cell values from an .img file, it just keeps
> > giving strange histogram values.  The plot() looks ok, except the legend
> > has those same useless values.  Similarly on the categorical NLCD Land
> > Cover layer it gives me data associated with each cell value (e.g. land
> > cover type), which is fine to work with, but still not the actual cell
> > values as I'd expect.  The old raster() function in raster package works
> > fine (see below). Thanks for insights! -Noah
> >
> > >   #Download Tree Canopy Layer from NLCD
> > >   #   https://www.mrlc.gov/data/nlcd-2016-usfs-tree-canopy-cover-conus
> > >
> > >   #terra package gives me nonsensical histogram values
> > >   library(terra)
> > >   canopy <- rast('D:/GIS/Land
> >
> Cover/nlcd_2016_treecanopy_2019_08_31/nlcd_2016_treecanopy_2019_08_31.img')
> > >   canopy
> > class       : SpatRaster
> > dimensions  : 104424, 161190, 1  (nrow, ncol, nlyr)
> > resolution  : 30, 30  (x, y)
> > extent      : -2493045, 2342655, 177285, 3310005  (xmin, xmax, ymin,
> ymax)
> > coord. ref. : Albers Conical Equal Area
> > source      : nlcd_2016_treecanopy_2019_08_31.img
> > color table : 1
> > categories  : Histogram, Red, Green, Blue
> > name        :  Histogram
> > min value   : 5737352684
> > max value   : 7854320129
> > >   plot(canopy)
> > >   canopy[50000,50000]
> >   Histogram
> > 1  24314964
> > >   extract(canopy,data.frame(x=1000000,y=1000000))
> >   ID Histogram
> > 1  1  44832754
> > >
> > >   #raster package works fine
> > >   library(raster)
> > >   canopy <- raster('D:/GIS/Land
> >
> Cover/nlcd_2016_treecanopy_2019_08_31/nlcd_2016_treecanopy_2019_08_31.img')
> > >   canopy
> > class      : RasterLayer
> > dimensions : 104424, 161190, 16832104560  (nrow, ncol, ncell)
> > resolution : 30, 30  (x, y)
> > extent     : -2493045, 2342655, 177285, 3310005  (xmin, xmax, ymin, ymax)
> > crs        : +proj=aea +lat_0=23 +lon_0=-96 +lat_1=29.5 +lat_2=45.5
> +x_0=0
> > +y_0=0 +datum=NAD83 +units=m +no_defs
> > source     : nlcd_2016_treecanopy_2019_08_31.img
> > names      : Histogram
> > values     : 0, 255  (min, max)
> > attributes :
> >         ID  Histogram Red Green Blue
> >  from:   0 5737352684 255   255  255
> >   to : 255 7854320129 255   255  255
> > >   canopy[50000,50000]
> > 24
> > >   extract(canopy,data.frame(x=1000000,y=1000000))
> > 94
> > >
> > >   #Land Cover (categorical) layer gives associated categories (not
> > values) in terra
> > >   #     https://www.mrlc.gov/data/nlcd-2019-land-cover-conus
> > >
> > >   nlcd <- rast('D:/GIS/Land
> >
> Cover/nlcd_2019_land_cover_l48_20210604/nlcd_2019_land_cover_l48_20210604.img')
> > >   nlcd
> > class       : SpatRaster
> > dimensions  : 104424, 161190, 1  (nrow, ncol, nlyr)
> > resolution  : 30, 30  (x, y)
> > extent      : -2493045, 2342655, 177285, 3310005  (xmin, xmax, ymin,
> ymax)
> > coord. ref. : Albers Conical Equal Area
> > source      : nlcd_2019_land_cover_l48_20210604.img
> > color table : 1
> > categories  : NLCD Land Cover Class, Histogram, Red, Green, Blue, Opacity
> > name        :        NLCD Land Cover Class
> > min value   :                 Unclassified
> > max value   : Emergent Herbaceous Wetlands
> > >   nlcd[50000,50000]
> >   NLCD Land Cover Class
> > 1      Evergreen Forest
> > >   extract(nlcd,data.frame(x=1000000,y=1000000))
> >   ID NLCD Land Cover Class
> > 1  1      Evergreen Forest
> > >
> >
> >
> > ~~~
> > Dr. Noah Charney (he/him)
> > Assistant Professor of Conservation Biology
> > Department of Wildlife, Fisheries, and Conservation Biology
> > University of Maine, Orono, ME
> > 230 Nutting Hall
> > (207) 581-1284
> >
> >         [[alternative HTML version deleted]]
> >
> > _______________________________________________
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> > R-sig-Geo using r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
>
>
> --
> Sarah Goslee (she/her)
> http://www.numberwright.com
>

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