Problem GeoTiff Reported
------------------------
Key: GEOT-3195
URL: http://jira.codehaus.org/browse/GEOT-3195
Project: GeoTools
Issue Type: Bug
Components: gc geotiff
Affects Versions: 2.6.5
Reporter: Jody Garnett
We have a problem geotiff reported; the file is available as an attachment to
the udig bug report.
{panel}
The geotiff consists of two images:
- A "scanned map" GeoTIFF, which is color-coded with 256 colors (or less) on 1
band.
- A "transparency mask," always present in the file. It identifies the padded
pixels wich have the color code "0" in the main picture.
The TIFF tag "SampleFormat" is set to "1" (default) to specify an encoding on
an unsigned integer value.
I do not know the library used to generate this file. It is likely a library
derived from GDAL.
The 'data' part of a ortho-image product type is composed of a single file
GeoTIFF. This file may contain two sub-files (as defined in the "subfile" TIFF
specification) and thus two IFD :
one for the image itself and one for the possible transparency mask. The image
itself is always described by the first IFD of the file.
The transparency mask is used to encode the notion of padding, in the usual
raster-spatial data.
The transparency mask is a dual level image which can be superimposed with the
picture described by the first IFD. The pixel value "1" means that the
corresponding pixel in the main image is significant (it is part of the active
area). Conversely, the pixel value "0" means that the corresponding pixel in
the image have an unknown value (it is a padding pixel) and typically must be
made transparent to the display.
A transparency mask contains no GeoTIFF tag. As part of this specification, it
was decided to use a mask with the same resolution and size as the main image.
The transparency mask is thus directly superimposed (pixel by pixel) in the
master image.
{panel}
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