Hello again,
Now that I've managed to use readGDAL successfully, I'd really like to
write some img files using writeGDAL, and I'm having some er,
interesting problems that I can't quite understand. Pardon the length
of the message.
For the most part, writeGDAL successfully writes an IMG file that I can
successfully read into ArcGIS, with projection and all. But sometimes
(from an identical writeGDAL command) the file comes up with no
projection and data values of all zeros. Checking this in R using
GDALinfo or readGDAL reveals the same thing - proj4string is NA and all
values are zero.
BUT, if I use readGDAL again on the same file, it works, and,
additionally, I can then successfully read it into ArcGIS.
I wonder if there is a buffer issue where the writeGDAL command doesn't
quite finish it's business until I nudge it with some other GDAL
commands. If I close R before I get the file to read in properly, then
no amount of readGDAL will get it to come in with projection and data
values.
I think one solution is to figure out the lower level commands like
GDAL.open and GDAL.close so I can close handles explicitly, but it would
be nice to use writeGDAL. Any ideas?
Here is a sample of the code that produced the problem.
> library(rgdal)
Loading required package: sp
Geospatial Data Abstraction Library extensions to R successfully loaded
> test <- readGDAL('swe20070220.img')
swe20070220.img has GDAL driver HFA
and has 360 rows and 720 columns
Closing GDAL dataset handle 0x0209ef78... destroyed ... done.
> summary(test)
Object of class SpatialGridDataFrame
Coordinates:
min max
x -180 180
y -90 90
Is projected: FALSE
proj4string :
[+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0]
Number of points: 2
Grid attributes:
cellcentre.offset cellsize cells.dim
x -179.75 0.5 720
y -89.75 0.5 360
Data attributes:
band1
Min. : 0.00
1st Qu.: 14.00
Median : 57.00
Mean : 63.02
3rd Qu.: 98.00
Max. : 480.00
NA's :225758.00
> writeGDAL(test, 'swe20070220_TEST.img', driver = 'HFA')
> test2 <- readGDAL('swe20070220_TEST.img')
swe20070220_TEST.img has GDAL driver HFA
and has 360 rows and 720 columns
Closing GDAL dataset handle 0x0218f760... destroyed ... done.
Closing GDAL dataset handle 0x020b72f8... destroyed ... done.
Closing GDAL dataset handle 0x0209f068... destroyed ... done.
> summary(test2)
Object of class SpatialGridDataFrame
Coordinates:
min max
x 0 720
y 0 360
Is projected: NA
proj4string : [NA]
Number of points: 2
Grid attributes:
cellcentre.offset cellsize cells.dim
x 0.5 1 720
y 0.5 1 360
Data attributes:
band1
Min. :0
1st Qu.:0
Median :0
Mean :0
3rd Qu.:0
Max. :0
> image(test2)
Closing GDAL dataset handle (nil)... done.
> rm(test2)
> test2 <- readGDAL('swe20070220_TEST.img')
swe20070220_TEST.img has GDAL driver HFA
and has 360 rows and 720 columns
Closing GDAL dataset handle 0x02187368... destroyed ... done.
> summary(test2)
Object of class SpatialGridDataFrame
Coordinates:
min max
x -180 180
y -90 90
Is projected: FALSE
proj4string :
[+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0]
Number of points: 2
Grid attributes:
cellcentre.offset cellsize cells.dim
x -179.75 0.5 720
y -89.75 0.5 360
Data attributes:
band1
Min. : 0.00
1st Qu.: 14.00
Median : 57.00
Mean : 63.02
3rd Qu.: 98.00
Max. : 480.00
NA's :225758.00
> version _
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 2
minor 5.0
year 2007
month 04
day 23
svn rev 41293
language R
version.string R version 2.5.0 (2007-04-23)
Many thanks in advance
--
**********************************
Matthew Landis
Research Analyst
Isciences, LLC
61 Main St., Suite 200
Burlington VT 05401 USA
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