| Re: Reading individual bits of MODIS BRDF quality files [message #68072] |
Mon, 21 September 2009 01:38 |
wita
Messages: 43
Registered: January 2005
|
Member |
|
|
>
> Is there a function in IDL that can read individual bits, or any other
> clever way to produce an array of 1s and 0s from a 32-bit integer?
Hi Edward,
Compile the function below and run it trough ENVI Band math and it
will return an 0/1 map of the bit position that you specify. So for
retrieving
bit position 7 (integer value 128) use:
cgi_map_bitwise_flag(b1, 7)
with best regards,
Allard
FUNCTION cgi_map_bitwise_flag, statusmap, bitposition
return, BYTE((statusmap AND (2UL^bitposition))/(2UL^bitposition))
END
|
|
|
|
| Re: Reading individual bits of MODIS BRDF quality files [message #68091 is a reply to message #68072] |
Fri, 18 September 2009 06:25  |
pgrigis
Messages: 436
Registered: September 2007
|
Senior Member |
|
|
On Sep 18, 5:54 am, emitchard <emitch...@googlemail.com> wrote:
[skip]
> Is there a function in IDL that can read individual bits, or any other
> clever way to produce an array of 1s and 0s from a 32-bit integer?
For the record (in case somebody needs that):
IDL> x=2LL^45+2LL^35+2LL^32+2LL^31+2LL^25+2LL^15+2LL^5-1 & print,x
35225207865375
;get only 32 bits
IDL> a=string(ulong(x),format='(B)') & print,a
10000010000000001000000000011111
;get all bits
IDL> a=string(x,format='(B)') & print,a
1000000000100110000010000000001000000000011111
Ciao,
Paolo
>
> Many thanks for your help,
>
> Edward Mitchard
|
|
|
|
| Re: Reading individual bits of MODIS BRDF quality files [message #68094 is a reply to message #68091] |
Fri, 18 September 2009 05:05 |
emitchard
Messages: 3
Registered: May 2008
|
Junior Member |
|
|
Please ignore this, I've solved the problem by writing to a temporary
file, opening it using readu as a byte array with four times as many
lines, reading the needed bytes and allowing the values I need through
an 'if' statement.
Apologies,
Edward
On Sep 18, 10:54 am, emitchard <emitch...@googlemail.com> wrote:
> I am running IDL 7.0.6 on Windows vista (with ENVI 4.6). I am using
> MODIS BRDF corrected 500 m data (MCD43A4). I have sucessfully written
> a program to open the HDF files and produce the output vegetation
> indices I'm interested in. However, I need to filter out cloud-
> contaminated pixels, and am having problem reading the bit-packed
> quality control file (MCD43A2).
>
> I have written a program to extract the layer I'm interested in from
> the HDF file and save it as a 32-bit unsigned integer. However, I
> really need to extract the raw values of the first 12 bits of this
> number (the values of the remaining fields do not matter to me). I
> started writing a program to list all the numbers (from 0-4294967295)
> that result from my required bit combination of these first 12 bits,
> but that approach is not going to work as there are several million
> 'allowable' numbers.
>
> Is there a function in IDL that can read individual bits, or any other
> clever way to produce an array of 1s and 0s from a 32-bit integer?
>
> Many thanks for your help,
>
> Edward Mitchard
|
|
|
|
| Re: Reading individual bits of MODIS BRDF quality files [message #68095 is a reply to message #68094] |
Fri, 18 September 2009 05:05 |
Wout De Nolf
Messages: 194
Registered: October 2008
|
Senior Member |
|
|
On Fri, 18 Sep 2009 02:54:55 -0700 (PDT), emitchard
<emitchard@googlemail.com> wrote:
> I am running IDL 7.0.6 on Windows vista (with ENVI 4.6). I am using
> MODIS BRDF corrected 500 m data (MCD43A4). I have sucessfully written
> a program to open the HDF files and produce the output vegetation
> indices I'm interested in. However, I need to filter out cloud-
> contaminated pixels, and am having problem reading the bit-packed
> quality control file (MCD43A2).
>
> I have written a program to extract the layer I'm interested in from
> the HDF file and save it as a 32-bit unsigned integer. However, I
> really need to extract the raw values of the first 12 bits of this
> number (the values of the remaining fields do not matter to me). I
> started writing a program to list all the numbers (from 0-4294967295)
> that result from my required bit combination of these first 12 bits,
> but that approach is not going to work as there are several million
> 'allowable' numbers.
>
> Is there a function in IDL that can read individual bits, or any other
> clever way to produce an array of 1s and 0s from a 32-bit integer?
>
> Many thanks for your help,
>
> Edward Mitchard
Maybe I don't understand what you want, but to extract the first
12bits from a 32bit integer:
a=54564L
b=a and 'FFF'xl
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
