Hanlie Pretorius wrote:
I have an existing CSV file that has the headers lat, long and precip.
The precipitation is a floating point number to two decimal places.
The coordinates in the CSV file define the centre of a quarter degree
square. The first set of coordinates in the file is -19.625,15.875.
Becuase the TRMM data defines the centre of the square, I subtracted
0.125 from the first set of coordinates to get the north-west corner
of the raster. And I added 0.125 to the last coordinate in the CSV
file, which is -34.875,34.125, to get the south-east corner of the
raster.
This seems wrong; positive-X is east, positive-Y is north, so you
should be adding to north and east, subtracting from south and west.
In the CSV file, the latitude stays constant for 74 rows while the
longitude increments in quarter degree steps. The whole file contains
4588 rows, so a grid of the data should have 74 rows and 62 columns,
right?
So I reformatted the data to 74 rows and 62 columns and added the header:
north: -19.5
south: -35.0
east: 15.75
west: 34.25
Positive-X is east, so either east and west are the wrong way around,
or they should both be negative, or this represents a span of 341.5
degrees.
rows: 74
cols: 62
null: -319.99
The output of g.region -p is:
projection: 3 (Latitude-Longitude)
zone: 0
datum: wgs84
ellipsoid: wgs84
north: 18S
south: 36S
west: 15E
east: 35E
Here, east and west have been swapped relative to what you say above.
nsres: 0:15
ewres: 0:15
rows: 72
cols: 80
cells: 5760
I then imported the reformatted file using the command:
r.in.ascii -f input=3B42RT.2010032409.6.bin.sa.grass\
output=2010032409.6.precip \
title=Precipitation 2010032409.6\
mult=1.0 or read from header nv=* or read from header
When imported, I get two thin strips of data on the sides of the
image. The raster shouldn't contain any nulls (the text file doesn't
contain the value -319.99), so something is wrong.
r.info gives a very strange resolutions:
| Type of Map: raster Number of Categories: 255
| Data Type:FCELL
| Rows: 74
| Columns: 62
| Total Cells: 4588
|Projection: Latitude-Longitude
|N: 19:30SS:35S Res: 0:12:34.054054
|E: 15:45EW: 34:15E Res: 5:30:29.032258
The west edge is east of the east edge, resulting in a span of 341.5
degrees. 341.5 / 62 = 5.508064516129032 = 5:30:29.032258.
| Range of data:min = 0.00 max = 7.47
Can someone perhaps help me to see what's happening here?
East and west are swapped.
--
Glynn Clements gl...@gclements.plus.com
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