RE: [Tcl-nap-users] Two issues : gdal +binary data

[<Har...@cs...>]

-----Original Message-----
From: tcl...@li...
[mailto:tcl...@li...] On Behalf Of salah
jubeh
Sent: Monday, 6 March 2006 22:53
To: NAP
Subject: [Tcl-nap-users] Two issues : gdal +binary data

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Hi Guys

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Since NAP is an array processor, and i think it is originally designed
to support images is there is any way to support GDAL format.

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I GDAL my images and convert them to ASCII or HDF image file and after
that make my manipulation, and this is an extra process.

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I was not aware of GDAL. I found web page:

http://www.remotesensing.org/gdal/index.html

This was most interesting.  GDAL looks very useful for converting from
one grid/raster file type to another.

There was a description of the GDAL data model. I gather this is an
internal (memory) format (like Nap's NAOs) rather than a file format. Is
this correct? If so, I do not understand what you mean by "support GDAL
format".  If it is a file format (binary I assume) then two
possibilities are:

1.	Read using command "nap_get binary"
2.	Implement a new Tcl image type. This involves writing C code.

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second issue:

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I create NAOs objects out of quick bird image and i did a comparison
between the time needed to create NAO out of ASCII and out of HDF

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i create 8 images 4 in ASCII and 4 in HDF  "each band in an image" and
i got this result.


Image Name

N_cols

Nrows

Data type

origen

Size ascii

Size HDF

Time ASCII

Time HDF

Diff


B_1

4698

2235

U16

Quick

34.624

20.531

17.078

244.11

227.032


B_2

4698

2235

U16

Quick

34.760

20.531

17.141

245.58

228.439


B_3

4698

2235

U16

Quick

31.29

20.531

17.203

248.39

231.187


B_3

4698

2235

U16

Quick

34.833

20.531

18.125

255.00

236.857

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is my result is ok...?, now i am wondering why creating NAO out of HDF
files is more expensive than creating it out of ASCII.

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  This makes no sense to me. ASCII should take much longer than HDF.=20

Your HDF file sizes look sensible, but not the ASCII sizes (unless some
form of compression is being used). Using your smallest ASCII size of
31.29 MB, this means there are only 31.29*(1024*1024.0)/(4698*2235*2) =
=3D
1.6 bytes per element.  The smallest space an ASCII value can occupy is
two bytes (e.g. "9,").

Would you like to send me sample HDF & ASCII files?