<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.2800.1106" name=GENERATOR></HEAD>
<BODY>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=906511317-25012008>Hi,</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=906511317-25012008></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=906511317-25012008>you work with georeferenced data and not with images.
Therefor you have to declare in the tfw-file the coordinate of the left upper
pixel in the correct projection. It could be that the gdal-tools have a program
to cut an georeferenced image into georeferenced tiles.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=906511317-25012008></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=906511317-25012008><!-- Converted from text/plain format -->
<P><FONT size=2>Mit freundlichen Grüssen<BR><BR>Arnd Wippermann<BR><A
href="http://gis.ibbeck.de/ginfo/">http://gis.ibbeck.de/ginfo/</A><BR><BR></FONT></P></SPAN></FONT></DIV>
<DIV dir=ltr align=left>
<HR tabIndex=-1>
</DIV>
<DIV dir=ltr align=left><FONT face=Tahoma size=2><B>Von:</B> UMN MapServer Users
List [mailto:MAPSERVER-USERS@LISTS.UMN.EDU] <B>Im Auftrag von
</B>Ian<BR><B>Gesendet:</B> Mittwoch, 23. Januar 2008 20:27<BR><B>An:</B>
MAPSERVER-USERS@LISTS.UMN.EDU<BR><B>Betreff:</B> [UMN_MAPSERVER-USERS] Tiff
world file question<BR></FONT><BR></DIV>
<DIV></DIV>SRTM3 data (.img format w/index) for a basemap is slow, so to speed
up our draw times I'm using a script to make smaller tiles of this data. My
script writes the images to .tif format and works, but I also need to generate
tiff world files to maintain spatial reference. The definition I found for the
.tfw format is: <BR><BR>First row is x-pixel resolution<BR>Second and third rows
are "rotational components" but are set to zero in the case of an unrotated
map.<BR>The fourth row is the y-pixel resolution. The negative sign indicates
that the image y-axis is positive down which is the opposite from real world
coordinates.<BR>The 5th and 6th rows are the Easting and Northing of the upper
left pixel (0,0 in image coordinates)<BR><BR>So for SRTM3 data which is 90m
resolution I am creating a .tfw file
like:<BR><BR>90.00<BR>0.00<BR>0.00<BR>-90.00 <BR>???<BR>???<BR><BR>The last two
rows are confusing me. Do I need to calculate the pixel position of the upper
left corner of each new tile with respect to the pixels of ALL SRTM3 files? That
calculation could be problematic. <BR><BR>Also if there is another tiling
solution that maintains spatial reference I'm all ears. Thank
you.<BR></BODY></HTML>