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:[EMAIL PROTECTED] > 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:[EMAIL PROTECTED] > > 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:[EMAIL PROTECTED] > > > Sent: Thursday, November 17, 2005 9:03 AM > > > To: Gambin Dejan; [email protected] > > > 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:[EMAIL PROTECTED] On Behalf Of Gambin Dejan > > > > Sent: 17 November 2005 15:39 > > > > To: [email protected] > > > > 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:[EMAIL PROTECTED] On Behalf Of > Ed McNierney > > > > > Sent: Thursday, November 17, 2005 12:43 AM > > > > > To: [email protected] > > > > > 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 > > > > > [EMAIL PROTECTED] > > > > > > > > > > -----Original Message----- > > > > > From: Dejan Gambin [mailto:[EMAIL PROTECTED] > > > > > Sent: Wednesday, November 16, 2005 6:07 PM > > > > > To: Ed McNierney > > > > > Cc: [email protected] > > > > > 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:[EMAIL PROTECTED] > > > > > > Sent: Wednesday, November 16, 2005 10:54 PM > > > > > > To: Dejan Gambin; [email protected] > > > > > > 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 > > > > > > [EMAIL PROTECTED] > > > > > > (978) 251-4242 > > > > > > > > > > > > -----Original Message----- > > > > > > From: Dejan Gambin [mailto:[EMAIL PROTECTED] > > > > > > 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:[EMAIL PROTECTED] > > > > > > > On Behalf Of Ed McNierney > > > > > > > Sent: Wednesday, November 16, 2005 4:51 PM > > > > > > > To: [email protected] > > > > > > > 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 > > > > > > > [EMAIL PROTECTED] > > > > > > > (978) 251-4242 > > > > > > > > > > > > > > -----Original Message----- > > > > > > > From: UMN MapServer Users List > > > > > > [mailto:[EMAIL PROTECTED] > > > > > > > On Behalf Of Gambin Dejan > > > > > > > Sent: Wednesday, November 16, 2005 8:59 AM > > > > > > > To: [email protected] > > > > > > > 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 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
