Zooming on images

[Stephen Lime]

Um, er... Scale calculations with DD data are broken. That is, since
x cellsize (no straight DD/in conversion) varies I didn't add the s
upport to calculate some average scale even though it's just an 
approximation. I got some equations  from the guys at Space Imaging 
and have added scale calculation support for DD units to the new 
version. With that version you'll be able to do exactly what you propose 
with the layer descriptions below.

** Note **

I'm interested in users opinions on this. Should scale for DD maps
be constant at a given zoom for anywhere on the globe (i.e. based
on cellsize in the y direction) or should it vary as you pan north or
south (i.e. based on the average cellsize in the x direction), or should it
be computed as some sort of average of the computed cellsize in
both directions? I'm leaning towards just using an average x cellsize
but am open to other points of view.

** end **

The scale problem only effect the minscale/maxscale piece but
you should be able to zoom in and out. (you'll have to pick an image
to use). You might try commenting out the minscale/maxscale stuff
and turning all rasters off except for 1 and see if that helps.

Got a "get" URL I can play with?

Steve

Stephen Lime
Internet Applications Analyst
MIS Bureau - MN DNR

(651) 297-2937
steve.lime at dnr.state.mn.us

>>> ddnebert <ddnebert at usgs.gov> 09/20 2:45 PM >>>
I have now four nice TIF images that I would like to use as backdrop to
other
data. The files are as follows with wld files that let them render fine
individually
at full extent.  If I try to set another extent in the GET request, I
still see the
whole world, rather than a zoomed in region.

shdrela.tif 640 x 320 TIF
shdrelb 2160 x 1080 TIF
shdrelc 4800 x 2400 TIF
shdreld 10800 x 5400 TIF

So I have two problems:

1. How do I make the registration correct?  I calculated the TFW files
as attached.

2. Once I can view one of the files, I'd like to set them up as a
cascade
of a single theme, broken by MINSCALE and MAXSCALE values.
Should the following work?

LAYER
  NAME shdrelief
  TYPE RASTER
  STATUS ON
  DATA shdrela.tif
  MINSCALE 5000000
  OFFSITE 0
END

LAYER
  NAME shdrelief
  TYPE RASTER
  STATUS ON
  DATA shdrelb.tif
  MINSCALE 3000000
  MAXSCALE 5000000
  OFFSITE 0
END

LAYER
  NAME shdrelief
  TYPE RASTER
  STATUS ON
  DATA shdrelc.tif
  MINSCALE 1000000
  MAXSCALE 3000000
  OFFSITE 0
END

LAYER
  NAME shdrelief
  TYPE RASTER
  STATUS ON
  DATA shdreld.tif
  MAXSCALE 1000000
  OFFSITE 0
END