[R-sig-Geo] intermittent writeGDAL problems

[Matthew Landis]

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