[Gdal-dev] IPCC raster format

[Ivan Lucena]

Hi there,

 

I would rather been watching the World Cup, but I have to get this data
in a usable format and there is no better place to get it than from
GDAL's experts.

 

The "Intergovernmental Panel on Climate Change" (IPCC) offers data on
the web in a format described by this Fortran source code: (The file
extension is just a generic ".dat")

 

http://ipcc-ddc.cru.uea.ac.uk/obs/observed_fileformat.html

 

> more cpre0130.dat

    grd_sz      xmin      ymin      xmax      ymax    n_cols    n_rows
n_months

      0.50      0.25    -89.75    359.75     89.75       720       360
12

...

-9999-9999-9999-9999-9999-9999-9999-9999-9999   52   88  103   91   65
45   27   32 ...

-9999-9999-9999-9999-9999   11   20   22   25   27   26   27   28   31
29   28   30 ...

...

 

It's not hard to analyze the pattern on the data or the code, so I
figured that:

 

- It's an ASCII format;

- There are two lines of reader (easy to read)

- Each cell is 5 characters wide;

- The no-data is "-9999";

- There is no separator between cells (what makes my task difficult);

- It's a multi-band raster dataset with 12 bands; (720x360x12 cells)

- I am not sure if positive values can go beyond 9999 (that reminds me
COBOL)

 

I am heading in the direction of writing a Python+GDAL script to do the
task, but I am stuck in how to separate the cells. The Fortran code is
doing it in just one command as you can see in the code. I am thing that
maybe by using the NumPY stuff embedded in GDAL I could do the same.

 

Any Idea? Any experience with this data format?

 

Thanks in advance,

 

Ivan

 

-------------------------------------------------------

This is a Python command line interaction with the data:

 

>>> import gdal

>>> f = open('C:/Data/IPCC/cpre0130.dat', 'r');

>>> f.readline()

'    grd_sz      xmin      ymin      xmax      ymax    n_cols    n_rows
n_months\n'

>>> f.readline()

'      0.50      0.25    -89.75    359.75     89.75       720       360
12\n'

>>> f.readline()

'-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-
9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-99
99-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999-9999
-9999-9999-9999-9999-9999-9

 

-------------------------------------------------------

Fortran source code:

 
program rd_ascii       
!
! f90 program to read in an integer ascii grid with
! variable dimensions into a global grid (720x360x12)
!
  parameter :: n_cols=720
  parameter :: n_rows=360
  integer, dimension (n_cols,n_rows,12) :: grid
  character(len=72) :: infl
  character(len=20) :: fmt
!
  call getarg(1,infl)
!       
  if(infl.eq.' ')then
    write(*,*) 'Enter ascii grid file name'
    read(*,'(a72)')infl
  end if
!       
  open(1,file=infl,status='old')
  read(1,*)
  read(1,*)xmin,ymin,xmax,ymax,ncols,nrows,nmonths,missing
  grid=missing
  fmt='( i5)'
  write(fmt(2:4),'(i3)')n_cols
  do im=1,nmonths
    do lat=1,n_rows
      read(1,fmt)(grid(lon,lat,im),lon=1,n_cols)
    enddo
  enddo
!       
end program rd_ascii

 

 

 

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