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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: GISList: JPEG (JPG) and JPEGW (JPW) |
| Date: |
01/07/2003 11:20:55 AM |
| From: |
David Nealey |
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Neil,
The .JPW files are the world files for the JPEG images. They serve the same
function as .TFW files for Tiff images.
The ArcView users manual explains quite clearly what the values mean. You
can also get an explanation of world files from the ESRI web site. But here
is what the AV manual says:
First value: The dimension of pixels in map units in the x-direction
(x-scale)
Second value: Rotation term for the rows
Third value: Rotation term for the columns
Fourth value: The dimension of a pixel in map units in the y-direction
(y-scale)
Fifth value: The x coordinate of the center of the upper-left pixel in map
units
Sixth value: The y coordinate of the center of the upper-left pixel in map
units
In order to account for differences between the origins of image and
non-image data, the x-scale is the negative of the y-scale.
Assuming that MapInfo reads world files, the extension .JPW may not be
understood by MapInfo. GeoMedia for example understands the extension .JGW.
So check your MapInfo users manual for the correct naming convention.
Also, the world file must be in the same directory as the JPEG files. Like
other GIS programs, MapInfo probably will not search your harddrive for the
corresponding .JPW files.
As for changing the values, I have never found an automated way to do it.
But you can probably adjust one image precisely through trial and error, and
then apply the same differentials to all of the world files. The trial and
error method is a pain but it works if your base map is registered exactly.
I hope that this helps. Let me know if you figure out a better way.
LDN
----- Original Message -----
From: "Neil Havermale" <neilh@redhensystems.com>
To: "Mapinfo-L (E-mail)" <MapInfo-L@lists.directionsmag.com>: "Gislist
(E-mail)" <gislist@geocomm.com>
Sent: Wednesday, January 01, 2003 12:02 AM
Subject: GISList: JPEG (JPG) and JPEGW (JPW)
> I have a number of USDA/NRCS aerial images. For each JPG image there is a
> companion file with the extension of JPW that includes what seems to be a
> UTM meters reference following UL and LR latice values for the image
> matix(?). Any help with importation without re-registration? The images
> are from Minnesota. Anyone with insight on this?
>
> 2.000000
> 0.000000
> 0.000000
> -2.000000
> 410000.000000
> 4932400.000000
>
> Also FYI, the NRCS has essentially 100 percent of most counties covered
with
> 1:600 B&W as well as color imagery used to establish farm MU (mapping
units)
> for various USDA compliance and other programs. It looks like in the MN
> case, they are providing these images as JPEGs free. Most counties likely
> also have these registered images certainly as scanable images or as
> binaries.
>
> Thanks,
> MidnIght Mapper
> aka neil
> PS Happy New Year - My resolutions is to survive one more year of this
> administration on the hope something good comes along....
>
>
>
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