Extents of a raster image

[Stephen Lime]

A good explanation. I must add that the mapserver expects world files to have the extension .wld and does not support the convoluted naming conventions of ESRI pre-arcview 3.1. This make life easier coding wise and makes the same world file usable with a variety of formats. Nice for testing anyway.

Steve

<<< "Brent Fraser" <bfraser at digitalscience.com>  7/21  6:40p >>>
If you mean how do you geo-reference a
raster image so MapServer places it correctly,
there are two ways:

    1. make the raster image a GeoTIFF
    2. create a "world" file for the image.

I've had better luck with the world file approach,
since not all applications read and write tiff tags
correctly.

Below is a short description of both.  If I
mis-understood your question, sorry for the
verbosity...

Brent
---------------------------------------------------------------------------
A TFW file is a short six line ASCII file that accompanies
a standard TIFF file to do basically the same thing as the
tags in a GeoTIFF (geo-reference a tiff image).

The format of an ESRI world file (*.tfw) is six values (one
per line) in an ascii file:

 pixel x size
 rotation about the y axis
 rotation about the x axis
 - pixel y size
 x of upper left pixel
 y of upper left pixel

For example:
--------------------------------
25
0.000000000000
0.000000000000
-25
657662.921000
6125428.836672
--------------------------------

The rotation values are always set to zero (until ESRI
supports rotation of raster files).   Note that the world
file has the same name as the TIFF file, but with an
extension of ".tfw".

GeoTiff uses the tiff format, with special tags embedded
right in the tiff file.  The tag numbers and what they
represent are:

33550 (0x830e)   <pixel x size> <pixel y size> <>
33922 (0x8482)    <> <> <> <x of upper left pixel> <y of upper left pixel>
<>

    There are a number of applications which will
display the GeoTIFF tags (Graphic Workshop is a
shareware example)


Brent Fraser
bfraser at geoanalytic.com



----- Original Message -----
From: <cshorte2 at csc.com>
To: <mapserver-users at lists.gis.umn.edu>
Sent: Wednesday, July 21, 1999 4:37 PM
Subject: Extents of a raster image


> How do I specify the extent of a raster image?
>
>
>