Subject: Re: Help:: opening a SPOT image w/ Photoshop on Mac

From: [email-masked] (Stephen McNeill)
Date: Sat, 4 Feb 1995 00:32:01 LOCAL

In article <[email-masked]> [email-masked] (Farmer Dan) writes:

>I need information on how to open a SPOT satalite image using Adobe Photoshop
>3.0 on a Mac Quadra using system 7.  Or else using Multispec, same system.

>The image size is about 3000X4000 with 3 interleaved bands, about 50Megs total
>size.   the Mac has 24Meg RAM, but we don't get a disk/full error message.  All
>we get are diagonal lines across where the image should be.  The image comes 
>with several files, but we have only been working with the image.dat file.

>Do I need to convert these images?  Should I be using a different application?

You don't specify how you have loaded these images exactly, but from the above
description, I presume you have a SPOT CD-ROM, correct ?  Since the image is 
3000 by 4000, you are probably dealing with a Multispectral level 1B image.  
Ok so far ?

If so, then you are probably dealing with a CEOS format disk (Committee on 
Earth Observing Systems). The format was formally known as the LGSOWG family 
format (pronounced "log-swog").  It seems a little unusual that the image is 
called "image.dat", since if it is a SPOT CD-ROM then the imagery file should 
have a name like "imag_01.dat" for the first image, "image_02.dat" for the 
second image on the disk etc.  This is the convention for CD-ROMs from SPOT 
Image at least, but perhaps you are dealing with a country variant.

The other little files are quite useful, since they give you volume, scene, 
and processing information.  You should really get a copy of the CEOS format, 
or the variant that was used to write your disk.

If you want a quick-fix to your problem of reading the data, the solution 
would be to read from the imagery file, but specifying the total record size 
for each imagery line, and if possible skipping the prefix data at the start 
of the line.  The records will be either 3960, 5400 or 8640 bytes long 
(from memory), so if you have "about 4000 pixels in a line" then you are 
probably dealing with the 5400 byte case (the most common).  Find out 
exactly how many !  Skip 32 bytes at the start of each line.  The first four 
bytes in each line will form a binary representation of the image record 
number.  The numbers should ascend, but very early SPOT data did sometimes 
descend.  You can find the length of the record in binary in bytes 9 to 12.

But this is only a quick-fix solution.  Ideally, you should read the rest of 
the small files scattered about and use those to work out the structure of the 
image.  It can get messy, but it is a widely used standard for remote sensing 
data for JERS/SPOT/Landsat and so on, although less so now with Landsat data 
since EOSAT's Fast Format is so much easier to deal with.

Of course, I could be barking up the wrong tree entirely...

If you get stuck, let me know.

WHAT !  You are at Carleton University ?  Do you realise how close that is to 
your CCRS ?  Where do you think this CEOS format was partly invented ?  Yes, 
you can probably guess...  Give them a ring...  Don't say I sent you, they 
wouldn't want to speak to me again.

Regards

Stephen McNeill
Image Processing Team
Landcare Research New Zealand Ltd
Box 38-491
Wellington Mail Centre
New Zealand

Phone:    +64-4-5690183
FAX:      +64-4-5690181
Internet: [email-masked]