Hi,
Re your (now bold text below) comment on jgw file.......
Simplistically, the 6 lines in a typical TFW style file represent:
1st line is left/right width and direction of pixel/cell
4th line is up/down height and direction of pixel.
5th and 6th are the coordinates (in whatever CRS) of the pixel described
in lines 1 & 4.
So in your case:
Pixel width is positive and size 2.68 units.
Pixel height is negative and size is also 2.68 (so raster pixels are
square).
So the coordinates in lines 5 and 6 are the position of the TOP (because
pixel height is negative) LEFT (*because pixel height is positive)
corner of your raster file.
Somewhere is the metadata you might find a reference as to whether the
coordinate represents the centre of the pixel or the corner (as
described) of the pixel - but this maybe noticeable if your image lands
up half a pixel size "wrong" in the real world.
HTH,
Zoltan
On 2026/06/28 15:54, Greg Troxel via QGIS-User wrote:
I am guessing this image is actually in Australia, in a rural area
"Alice Creek Nature Refuge", west of Brisbane?
I would suggest talking to the people who published this and asking them
for the CRS. At least trying. I find it very puzzling that it's close
to 3857 but not really. I'd expect some UTM in some version of GDA, or
some conventional grid that's TM or Lambert Conformal Conic or similar,
analogous to the US "State Plane Coordindate System. But maybe it's
published for normie web mapping.
When you say "without the jgw", do you mean you put the JPG file in a
directory (without the jgw file in the directory!!) and then try to add
the file in the georeferencer? You can do this without having the file
as a layer - that's what I've always done.
I also suggest trying the same thing with 3.44.x, on a different
computer if necessary to avoid messing up your installation. I switch
back and forth to test the in-progress qgis4 packaging, but I'm using
pkgsrc on NetBSD and I don't know what OS you are on, so that may be
harder.
*The jgw file is odd. The first 4 are, AIUI, supposed to be a rotation
matrix between pixels and the CRS. Then the coordinates of I think the
upper left pixel (either center or upper left of it, don't remember).*
Your per-pixel sizes are 2.69 (projected units per pixel, I think -
been a while), which seems normal enough, but there are values of
-4.946801637500726e-16
for the cross terms (easting for verticla change, northing for
horizontal change). This is effectively zero. I would not expect it to
be confounding. You could try with a jgw file with those modified to
0.0000000000.
When I look at tfw file for a US historic topo map, the first 4 values
are:
2.6822400000
0.0000000000
0.0000000000
-2.6822400000
but there is a .prj file which is the original map projection, so by
definition it is lined up precisely.
Not that my projection file could possibly be relevant to .au, but FWIW
it's
PROJCS["Polyconic",GEOGCS["GCS_North_American_1927",DATUM["D_North_American_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Polyconic"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-71.5625],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1]]
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=============================================
Zoltan Szecsei GPrGISc 0031
Director, Geograph (Pty) Ltd.
GIS and Photogrammetric Services
Cape Town, South Africa.
Mobile: +27-83-6004028 (Signal, not WhatsApp)
+36-20-3594428
www.geograph.co.za
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