Georeferencing tiff by creating tfw file
Gambin Dejan
Dejan.Gambin at PULA.HR
Thu Nov 17 23:13:08 PST 2005
Thanks, I understand what you have been told me BUT,
When I put my tiff on the map using "my" cellsize of 0.0021166, it
doesn't show correctly on the map (I just get a litte box bottomleft).
But if I use the cellsize of 0.08467878514170, then it is correctly
shown. That is the thing I didn't understand.
(I have already reported my error in first gdalinfo because it was run
with my already existing tfw file. I have reported the new gdalinfo
output after...)
Sorry again to bother you
best regards
dejan
> -----Original Message-----
> From: Delfos, Jacob [mailto:jacob.delfos at maunsell.com]
> Sent: Thursday, November 17, 2005 11:57 PM
> To: Gambin Dejan
> Subject: RE: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> creating tfw file
>
>
> The TIFFTAG_RESOLUTIONUNIT was set to pixels per inch (dpi).
> This is a "graphical" parameter embedded in many images
> (geographic or not). It is not related to real-world
> coordinates, but to paperspace only. It tells you how many
> pixels go into an inch, so that it can be printed at the same
> size as the original was.
> You are right about cellsize: it expresses how many metres in
> real-world coordinates one cell takes up. So this has been
> calculated using the TIFFTAG_RESOLUTIONUNIT, and combining
> that with the scale information.
>
> If the figures and units you give are correct, then:
> Your original scan is 300dpi, 1:25.
> So: 1 pixel = 1/300 inch in paperspace
> = 25 * 1/300 inch in real-world space
> = 0.08333 inch in real-world space
> = 0.002116 metres in real-world space
> So your pixel size (real-world space) is roughly 0.0021166m,
> as your gdalinfo output mentioned below. So make sure you
> understand which values are in geographic space, and which in
> paperspace.
>
> > pixel size in inches = scale/resolution, so 25.40363554/300 and
> > converting it to meters gives me 0.002150841. But this is
> not correct,
> right?
> > Wiht CAD overlay I have got 0.08467878514170, that is probably
> right...
>
> Both are right, but your CAD overlay reported the cellsize in
> real-world inches, your calculation gave it in metres.
>
> Regards,
>
> Jacob
>
>
>
>
> > -----Original Message-----
> > From: Gambin Dejan [mailto:Dejan.Gambin at pula.hr]
> > Sent: 17 November 2005 16:18
> > To: Delfos, Jacob
> > Subject: RE: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > creating tfw file
> >
> > No you didn't confuse me, thanks. But I am still not sure
> in what is
> > wrong in my calculation? Is the TIFFTAG_RESOLUTIONUNIT important
> > anyway? Does the CELLSIZE mean "the pixel has CELLSIZE meters" or?
> >
> > Sorry for bothering you
> >
> > dejan
> >
> > > -----Original Message-----
> > > From: Delfos, Jacob [mailto:jacob.delfos at maunsell.com]
> > > Sent: Thursday, November 17, 2005 9:03 AM
> > > To: Gambin Dejan; MAPSERVER-USERS at LISTS.UMN.EDU
> > > Subject: RE: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > creating tfw file
> > >
> > >
> > > Dejan,
> > >
> > > I think you are mixing up scale and resolution: scale is
> > > ratio between the real world and whatever you are looking at
> > > (hardcopy, screen, etc). So 1:25 means 1 unit on the screen
> > > equals 25 units in the real world (whichever units, as you said).
> > >
> > > Resolution expresses how many pixels go into a fixed length
> > > (expressed in a unit). It is necessary to have a unit,
> > > because obviously the result between 300 pixels in a metre,
> > > or 300 pixels in an inch, will be different. So
> > > "metres/pixel" is a resolution, NOT a scale. Metres/pixel
> > > tells you have many metres a pixel is, either on your screen
> > > or on a hardcopy. This does NOT tell you how many metres it
> > > is in the real world (geographic space). You need scale AND
> > > resolution to determine that.
> > >
> > > Hope I didn't confuse you further.
> > >
> > > Jacob
> > >
> > >
> > > > -----Original Message-----
> > > > From: UMN MapServer Users List
> > > > [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of Gambin Dejan
> > > > Sent: 17 November 2005 15:39
> > > > To: MAPSERVER-USERS at LISTS.UMN.EDU
> > > > Subject: Re: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > > creating tfw file
> > > >
> > > > Thanks Ed, thanks Jacob,
> > > >
> > > > That is the thing I have missed - the scale reported is in
> > > > "meters/pixel" and this gives the correct result....but
> > correct me
> > > > please - isn't the scale "unitsless" parameter? 1inch on
> > > map=25inch in
> > > > world, 1m on map=25m in world? I was looking in gdalinfo
> > output and
> > > > the TIFFTAG_RESOLUTIONUNIT that is set to pixel/inch, so I
> > > did 25/300
> > > > thinking it is the pixel size in inches that needs to be
> > > converted to
> > > > meters...obviously wrong
> > > >
> > > > regards, dejan
> > > >
> > > > > -----Original Message-----
> > > > > From: UMN MapServer Users List
> > > > > [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of
> Ed McNierney
> > > > > Sent: Thursday, November 17, 2005 12:43 AM
> > > > > To: MAPSERVER-USERS at LISTS.UMN.EDU
> > > > > Subject: Re: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > > > creating tfw file
> > > > >
> > > > >
> > > > > Dejan -
> > > > >
> > > > > "..if the map is in 1:25 scale, that means that 1 inch on the
> > > > > map is 25 inches in the real world....if the map was
> scanned on
> > > > > 300dpi then the pixel size is 25/300 in inches, then
> converted
> > > > > to meters"
> > > > >
> > > > > Yes, that's all there is to it. There's nothing more to
> > > > > understand. If the scale you're reporting in CAD
> Overlay is in
> > > > > units of "meters per pixel", then one pixel is
> 0.08467878514170
> > > > > meters. If that image were scanned at 600 DPI, then
> each inch
> > > > > on the printed map source would produce 600 pixels or 50.80
> > > > > meters. 50.80 meters is 2,000 feet, so that would
> correspond to
> > > > > a scale of 1" = 2,000' or 1:24,000 scale. Or it could be a
> > > > > 1:12,000 scale map scanned at 300 DPI - or a 1:48,000
> scale map
> > > > > scanned at 1,200 DPI. They would all come out the same - the
> > > > > image resolution in units per pixel is a product of
> the source
> > > > > scale and the scanning resolution, and you can't
> distinguish the
> > > > > two.
> > > > >
> > > > > - Ed
> > > > >
> > > > > Ed McNierney
> > > > > President and Chief Mapmaker
> > > > > TopoZone.com / Maps a la carte, Inc.
> > > > > 73 Princeton Street, Suite 305
> > > > > North Chelmsford, MA 01863
> > > > > Phone: +1 (978) 251-4242
> > > > > Fax: +1 (978) 251-1396
> > > > > ed at topozone.com
> > > > >
> > > > > -----Original Message-----
> > > > > From: Dejan Gambin [mailto:dejan.gambin at pula.hr]
> > > > > Sent: Wednesday, November 16, 2005 6:07 PM
> > > > > To: Ed McNierney
> > > > > Cc: MAPSERVER-USERS at LISTS.UMN.EDU
> > > > > Subject: RE: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > > > creating tfw file
> > > > >
> > > > > Sorry I forgot to set the CC..
> > > > >
> > > > > I have received this tif file from a colleague who wanted to
> > > > > "georeference" it and place it on the existing
> mapserver map. He
> > > > > just sent me the upper left coordinates (real world
> coordinates
> > > > > in meters) and this scale. Suppose he scanned the
> paper map that
> > > > > is in 1:25 scale and gave me the coordinates of the
> upper left
> > > > > corner. So I thought:
> > > > >
> > > > > ..if the map is in 1:25 scale, that means that 1 inch
> on the map
> > > > > is 25 inches in the real world....if the map was scanned on
> > > > > 300dpi then the pixel size is 25/300 in inches, then
> converted
> > > > > to meters. But it is not and obviously I am pretty newbie in
> > > > > this geo-math and I am missing some important things.
> > > > >
> > > > > Anyway, after a while he sent me a tfw file saying he
> has built
> > > > > it with CAD Overlay...that is all I know and this tiff is now
> > > > > positioned well on the map...
> > > > >
> > > > > ...Sorry, I am just curious in how this is
> > > > > theoretically/mathematically calculated so I asked....
> > > > >
> > > > > This is also interesting to me because we have some
> > > > > non-referenced tiff maps with some known world coordinates on
> > > > > them and I would like to georeference them in the future, if
> > > > > this is possible...
> > > > >
> > > > > regards, dejan
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Ed McNierney [mailto:ed at topozone.com]
> > > > > > Sent: Wednesday, November 16, 2005 10:54 PM
> > > > > > To: Dejan Gambin; MAPSERVER-USERS at LISTS.UMN.EDU
> > > > > > Subject: RE: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > > > creating tfw
> > > > >
> > > > > > file
> > > > > >
> > > > > >
> > > > > > Dejan -
> > > > > >
> > > > > > Well, that's not the GeoTIFF output you posted the
> > > first time <g>!
> > > > > >
> > > > > > What is the "scale" you have (the value that's
> > > 25.40363554)? What
> > > > > > is the definition of that value, and its units (if
> > > any)? And what
> > > > > > are the definition and the units of the "CAD Overlay"
> > > output, too?
> > > > > > It's hard to work with dimensionless,
> > > > > undefined numbers
> > > > > > - where did they come from? We need some more details to
> > > > be able to
> > > > > > help. Thanks!
> > > > > >
> > > > > > - Ed
> > > > > >
> > > > > > P.S. Please always reply to the whole list, not just
> > > to the first
> > > > > > responder.
> > > > > >
> > > > > > Ed McNierney
> > > > > > President and Chief Mapmaker
> > > > > > TopoZone.com / Maps a la carte, Inc.
> > > > > > 73 Princeton Street, Suite 305
> > > > > > North Chelmsford, MA 01863
> > > > > > ed at topozone.com
> > > > > > (978) 251-4242
> > > > > >
> > > > > > -----Original Message-----
> > > > > > From: Dejan Gambin [mailto:dejan.gambin at pula.hr]
> > > > > > Sent: Wednesday, November 16, 2005 4:31 PM
> > > > > > To: Ed McNierney
> > > > > > Subject: RE: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > > > creating tfw
> > > > >
> > > > > > file
> > > > > >
> > > > > > Ed,
> > > > > >
> > > > > > Sorry, I have run gdalinfo on the tiff with already
> > > > > existing tfw file
> > > > > > that I have calculated and that is WRONG...
> > > > > >
> > > > > > Running gdalinfo on this tif (that has no associated tfw)
> > > > > results in:
> > > > > >
> > > > > > Driver: GTiff/GeoTIFF
> > > > > > Size is 8857, 5905
> > > > > > Coordinate System is `'
> > > > > > Metadata:
> > > > > > TIFFTAG_XRESOLUTION=300
> > > > > > TIFFTAG_YRESOLUTION=300
> > > > > > TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch) Corner Coordinates:
> > > > > > Upper Left ( 0.0, 0.0)
> > > > > > Lower Left ( 0.0, 5905.0)
> > > > > > Upper Right ( 8857.0, 0.0)
> > > > > > Lower Right ( 8857.0, 5905.0)
> > > > > > Center ( 4428.5, 2952.5)
> > > > > > Band 1 Block=8857x5905 Type=Byte, ColorInterp=Palette
> > > > > > Color Table (RGB with 2 entries)
> > > > > > 0: 255,255,255,255
> > > > > > 1: 0,0,0,255
> > > > > >
> > > > > > So, I have this output, I have xy coordinates (in
> > > meters): 5455750
> > > > > > and 5021000 and I have the scale of 25.40363554.
> > > > > The question
> > > > > > remains - how do I calculate the "pixel size" (first
> > and fourth
> > > > > > parameter) of tfw file that I need to create.
> > > > > >
> > > > > > Using CAD Overlay I get the value of 0.08467878514170 that
> > > > > is correct
> > > > > > but I need to know how to get this value by formula, not
> > > > with util
> > > > > > like CAD Overlay
> > > > > >
> > > > > > Sorra again
> > > > > >
> > > > > > regards, dejan
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: UMN MapServer Users List
> > > > > > [mailto:MAPSERVER-USERS at LISTS.UMN.EDU]
> > > > > > > On Behalf Of Ed McNierney
> > > > > > > Sent: Wednesday, November 16, 2005 4:51 PM
> > > > > > > To: MAPSERVER-USERS at LISTS.UMN.EDU
> > > > > > > Subject: Re: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > > > > creating tfw
> > > > > >
> > > > > > > file
> > > > > > >
> > > > > > >
> > > > > > > Dejan -
> > > > > > >
> > > > > > > The gdalinfo utility is telling you the pixel size. The
> > > > > fourth line
> > > > >
> > > > > > > of the output below, beginning with "Origin = ", ends with
> > > > > > "Pixel Size
> > > > > >
> > > > > > > = ". Those are the very same values you would use in
> > > > the first and
> > > > > > > fourth lines, respectively, of a TFW file. It looks like
> > > > > > this is the
> > > > > > > same value you calculated, and it appears to be correct.
> > > > > > >
> > > > > > > - Ed
> > > > > > >
> > > > > > > Ed McNierney
> > > > > > > President and Chief Mapmaker
> > > > > > > TopoZone.com / Maps a la carte, Inc.
> > > > > > > 73 Princeton Street, Suite 305
> > > > > > > North Chelmsford, MA 01863
> > > > > > > ed at topozone.com
> > > > > > > (978) 251-4242
> > > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: UMN MapServer Users List
> > > > > > [mailto:MAPSERVER-USERS at LISTS.UMN.EDU]
> > > > > > > On Behalf Of Gambin Dejan
> > > > > > > Sent: Wednesday, November 16, 2005 8:59 AM
> > > > > > > To: MAPSERVER-USERS at LISTS.UMN.EDU
> > > > > > > Subject: [UMN_MAPSERVER-USERS] Georeferencing tiff by
> > > > creating tfw
> > > > > > > file
> > > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > Even there are probably some utils I can use, I would
> > > > > still like to
> > > > > > > know how can I calculate the "pixel size" parameter in
> > > > > tfw file (so
> > > > > > > the first and fourth parameter) from the existing tiff
> > > > > file and the
> > > > > > > following
> > > > > > > informations:
> > > > > > >
> > > > > > > For example, "gdalinfo my.tif" says
> > > > > > >
> > > > > > > Driver: GTiff/GeoTIFF
> > > > > > > Size is 8857, 5905
> > > > > > > Coordinate System is `'
> > > > > > > Origin = (5455749.998925,5021000.001075) Pixel Size =
> > > > > > > (0.00215084,-0.00215084)
> > > > > > > Metadata:
> > > > > > > TIFFTAG_XRESOLUTION=300
> > > > > > > TIFFTAG_YRESOLUTION=300
> > > > > > > TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch) Corner
> > > > > Coordinates: Upper
> > > > > > > Left ( 5455749.999, 5021000.001) Lower Left (
> 5455749.999,
> > > > > > > 5020987.300) Upper Right ( 5455769.049,
> > > > > > > 5021000.001) Lower Right ( 5455769.049, 5020987.300)
> > > > > > > Center ( 5455759.524, 5020993.651)
> > > > > > > Band 1 Block=8857x5905 Type=Byte, ColorInterp=Palette
> > > > > > > Color Table (RGB with 2 entries)
> > > > > > > 0: 255,255,255,255
> > > > > > > 1: 0,0,0,255
> > > > > > >
> > > > > > > I have xy coordinates (in meters): 5455750 and 5021000
> > > > > and the scale
> > > > >
> > > > > > > of 25.40363554. I have tried using the simple
> formula like:
> > > > > > >
> > > > > > > pixel size in inches = scale/resolution, so
> > > 25.40363554/300 and
> > > > > > > converting it to meters gives me 0.002150841. But this is
> > > > > > not correct,
> > > > > >
> > > > > > > right?
> > > > > > >
> > > > > > > Wiht CAD overlay I have got 0.08467878514170, that is
> > > probably
> > > > > > > right...
> > > > > > >
> > > > > > > What am I doing wrong? Is it the resolution that I am
> > > > using? Do I
> > > > > > > have to use screen resolution or what?
> > > > > > >
> > > > > > > thanks
> > > > > > >
> > > > > > > regards, dejan
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
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