Can PNG, JPG and WBMP files be georeferenced and stored that way?
Craig Mackay
Can PNG, JPG and WBMP files be georeferenced and stored that way? Like GeoTiff?
Any information on this would be appreciatedPaul Cooper
that holds georeferencing information - it is an extension of the
standard TIFF format. TIFF is by design extensible, so this is
straightforward. The other image formats are less extensible, so you
can't do it within the file. However, you can use an ancillary file
called a world file to specify the conversion between pixel coordinates
and map coordinates. The format of this file (if it is available in your
GIS) may vary. ESRI products use the following 6 parameter affine
transformation:
If
X1 = Ax + By + C
Y1 = Dx + Ey + F
Where X1,Y1 are map coordinates and x,y are pixel coordinates
The the world file contains the parameters A - F in the order
A,D,B,E,C,F, each on a separate line. E is normally negative because
images are often stored from top to bottom, requiring the Y dimension to
be inverted. If the image is aligned parallel to the coordinate system
then D and B will be zero, A and B will be the pixel size and C and F
will be the map coordinates of the first pixel.
World files are usually named with a suffix such as tfw for TIFF.
Paul
Stichting ST
wrote:
>Can PNG, JPG and WBMP files be georeferenced and stored that way? Like GeoTiff?
>
>Any information on this would be appreciated
>
>Regards
For the png format see:
http://gis.nrcan.gc.ca/webgis/webmap7.htm
where is told:
"PNG is the most useful of the raster imagery formats for GIS use. The
extensibility of the format means that georeferencing capability could be
incorporated as a tagged data block. Other metadata information such as
spheroid, projection, and vertical datum could also be stored. "
yes 'could' but I do not know of any implementation. Somewhere I found a
remark (sorry cannot trace it back) about the GeoTIFF geo-information being in
special fields in the picturefile 'the same way as PNG makes this possible'.
Piet