| reading unformatted data into a structure [message #29751] |
Mon, 18 March 2002 17:40 |
Rick Towler
Messages: 821
Registered: August 1998
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Senior Member |
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I have an unformatted data file which I am trying to read and I am having
only limited success. The data file was created on a Sun machine and it is
being read on a win32 machine (I have set the swap_if_little_endian keyword
on the open statement). As for the file format, all I have to go on is the
C header file that describes the records in the file.
Early on in the header I find this:
// Variable types:
// int is 32 bit integer.
// short is 16 bit integer.
Here are the first few lines of the header (all of the data types found in
the header are in these lines):
typedef struct
{
int fileFormatVersion; /* The file format version number. */
int points; /* Number of xyz points on the file. */
int time; /* UNIX time of file generation,
seconds since 1/1 1970. */
unsigned short coordSys; /* The coordinate system used:
0 = Geographical lat/long.
1 = Projection */
char projection[32]; /* Projection name (see above) */
int projParam1; /* 1. projection parameter (see above). */
int projParam2; /* 2. projection parameter (see above). */
int projParam3; /* 3. projection parameter (see above). */
int projParam4; /* 4. projection parameter (see above). */
int projParam5; /* 5. projection parameter (see above). */
char datum[32]; /* Name of the datum (see above). */
char ellLargeHalfAxis[16]; /* Large half axis of the ellipsoide. */
....
From the comments about variable types and the structure definition I
created an IDL structure that I think matches the C struct (again, I'll list
the first few lines):
header = { fileFormatVersion:0L, $
points:0L, $
time:0L, $
coordSys:0, $
projection:bytarr(32), $
projParam1:0L, $
projParam2:0L, $
projParam3:0L, $
projParam4:0L, $
projParam5:0L, $
datum:bytarr(32), $
ellLargeHalfAxis:bytarr(16), $
....
I open the data file and read the header like so:
openr, lun, 'J:\hydrographic\1.xyz', /get_lun, $
/swap_if_little_endian
readu, lun, header
Am I doing this correctly? I know I am close because I get what seems like
a valid time and I know I get a valid datum. But my data doesn't seem
right. I just want to check that I am using the correct types in my IDL
struct and that I am reading in the data correctly.
Also, I know I have seen this but how do I convert the decimal ASCII chars
in my bytarr's to a string?
Thanks.
-Rick
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