[R-sig-Geo] issue when opening raster image in R, the pixel values a rescaled somehow

[Roger Bivand]

Opening in stars shows that the read data are interpreted as degrees 
Kelvin:

> library(stars)
> ss <- read_stars("MOD11A2.A2000049.h17v05.006.2015058135048.tif")
> print(ss, n=1e8)
stars object with 2 dimensions and 1 attribute
attribute(s):
  MOD11A2.A2000049.h17v05.006.2015058135048.tif [K]
  Min.   :272.1
  1st Qu.:293.3
  Median :296.5
  Mean   :296.1
  3rd Qu.:298.8
  Max.   :309.2
  NA's   :926190
dimension(s):
   from   to   offset    delta  refsys point values
x    1 1200 -1111951  926.625 unnamed FALSE   NULL [x]
y    1 1200  4447802 -926.625 unnamed FALSE   NULL [y]

The summary agrees with

> library(rgdal)
> o <- readGDAL("MOD11A2.A2000049.h17v05.006.2015058135048.tif")
> summary(o)
Object of class SpatialGridDataFrame
Coordinates:
        min     max
x -1111951       0
y  3335852 4447802
Is projected: TRUE
proj4string :
[+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +R=6371007.181 +units=m +no_defs]
Grid attributes:
   cellcentre.offset cellsize cells.dim
x          -1111487 926.6254      1200
y           3336315 926.6254      1200
Data attributes:
      band1
  Min.   :272.1
  1st Qu.:293.3
  Median :296.5
  Mean   :296.1
  3rd Qu.:298.8
  Max.   :309.2
  NA's   :926190

and

> library(raster)
> r <- raster("MOD11A2.A2000049.h17v05.006.2015058135048.tif")
> summary(values(r))
    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.    NA's
   272.1   293.3   296.5   296.1   298.8   309.2  926190

So my feeling is that the representation is correct in degrees Kelvin.

Others please join in, I'm not familiar with MODIS HDF data. I think 
something gives the metadata in the GeoTIFF the wrong data bounds - they 
do seem to be UInt16. The output of gdalinfo (command line) includes:

...
   units=K
   valid_range=7500, 65535
...
Band 1 Block=1200x3 Type=UInt16, ColorInterp=Gray
   NoData Value=0
   Unit Type: K
...

Roger


On Tue, 24 Mar 2020, Victor F. Rodriguez Galiano wrote:

> Hi Roger, the link to he image is given below. This image was generated
> from a .hdf file using the function gdal_translate.
>
> gdal_translate(sds[1], dst_dataset=paste0(substr(filename, 1,
> nchar(filename)-4) ,".tif", ))
>
> https://wetransfer.com/downloads/4569e9a85c02faad5016b83d0b50217820200324084015/f2eafdfafaae74de9ac8e25017fc5cc520200324084015/e46e80
>
>
> Thanks
>
> Victor
>
> El lun., 23 mar. 2020 a las 21:07, Roger Bivand (<Roger.Bivand using nhh.no>)
> escribió:
>
>> Please make the file in question available for download (url), or the url
>> you downloaded it from (no login), on this list. It looks as though the
>> unsigned 16 bit integer is not right.
>>
>> Roger Bivand
>> Norwegian School of Economics
>> Bergen, Norway
>>
>> ------------------------------
>> *Fra:* R-sig-Geo <r-sig-geo-bounces using r-project.org> på vegne av Victor F.
>> Rodriguez Galiano <vrgaliano using gmail.com>
>> *Sendt:* mandag 23. mars 2020, 21.02
>> *Til:* r-sig-geo using r-project.org
>> *Emne:* [R-sig-Geo] issue when opening raster image in R, the pixel
>> values a rescaled somehow
>>
>> I opened a Geotiff image in R using the raster function. However, the
>> image seems to be rescaled. The minimum and maximum values should be 13607
>> and 15461 but are 275 and 305. The Geotiff image when opened in a GIS is
>> correct but not in R. This is my code: Script: library(raster)
>> trial<-raster("MOD11A2.A2000049.h17v05.006.2015058135048.tif", datatype =
>> "INT2U") trial plot(trial) [[alternative HTML version deleted]]
>> _______________________________________________ R-sig-Geo mailing list
>> R-sig-Geo using r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>

-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: Roger.Bivand using nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en