[Qgis-user] Is location info included in metadata when save an image file?
Kirk Schmidt
kirk at nortekresources.com
Tue Jun 4 10:27:24 PDT 2019
Ert:
With a jpg or png file, the coordinate data are stored in the world file
(a simple text file with the pixel x gsd , rotation,pixel y gsd, x
coordinate, top left, y coordinate top left - see sample below). For a
pdf, the coordinate data is stored within the pdf and you would have to
check the geo-pdf specs to see where they are stored. If you write a
geotiff, the coordinates will be contained withing the file header.
Sample tiff world file (*.tfw)
0.0250000000
0.000000
0.000000
-0.0250000000
674643.3881379978
4945024.4282323727
Kirk
On 6/4/2019 1:48 PM, Alex M wrote:
> Nyall,
>
> I just did a test like Kirk png and jpg do not contain EXIF coordinates.
> For the purposes of this discussion the original poster wants to know
> which formats drop the location data, and it appears jpg and png are
> safe for that purpose. I would advise that not every format will behave
> the same, as we all seem to agree a tiff from the Image Save should have
> the location in it's metadata. Though I know a good way to strip that
> out - GIMP or Photoshop, open & export usually kills all metadata,
> command line Photography tools might also (e.g. imagemagick).
>
> Tested with QGIS 3.4
>
> Thanks,
> Alex
>
> On 6/3/19 16:16, Nyall Dawson wrote:
>> On Tue, 4 Jun 2019 at 09:13, Fernando M. Roxo da Motta <petro at roxo.org> wrote:
>>> On Mon, 3 Jun 2019 11:01:06 -0300, Kirk Schmidt
>>> <kirk at nortekresources.com> wrote:
>>>
>>>
>>>> Hi Ert:
>>>>
>>>> You can save locational data in jpg and pdf files from within the
>>>> Print Composer window. Under composition tab on the right hand side
>>>> of the window, scroll down and check the Save World File checkbox.
>>>> Export your map/composition as a jpg or pdf and the geolocation data
>>>> will be written to a world file for a jpg and internally for a pdf.
>>> Just to be sure that I understood it correctly. If I save as jpg
>>> the geolocation information will be only written to the world file if I
>>> check the Save World File checkbox. That means that, regardless to
>>> check or not that checkbox, the jpg image will not contain any
>>> geolocation information.
>>>
>>> Is that correct?
>> Incorrect. It will always be embedded directly inside the image
>> metadata where possible. The "create world file" checkbox only
>> controls whether an external text file with the referencing
>> information is also created.
>>
>> Nyall
>>
>>>
>>>> Good luck
>>>>
>>>> Kirk Schmidt
>>>>
>>>> On 6/2/2019 4:26 AM, Ert Four wrote:
>>>>> Thank you Alex and Roxo for your replies.
>>>>>
>>>>> From what I can tell the SVG and JPG files probably don't have
>>>>> location info in them, but it's also hard to tell what exactly the
>>>>> data is in some places, especially in the SVG.
>>>>>
>>>>> It looks like qgsmaprenderertask.cpp was written two years ago,
>>>>> which was after 2.14 came out.
>>>>>
>>>>> I will post on the developer list per Alex's suggestion. All of
>>>>> this is trying to prove that something doesn't exist -- which is
>>>>> always hard.
>>>>>
>>>>> Thanks again.
>>>>>
>>>>>
>>>>>> On June 1, 2019 at 4:41 PM "Fernando M. Roxo da Motta"
>>>>>> <petro at roxo.org> wrote:
>>>>>>
>>>>>>
>>>>>> On Thu, 30 May 2019 17:09:59 +0200 (CEST), Ert Four
>>>>>> <4ert at mailbox.org> wrote:
>>>>>>
>>>>>>
>>>>>>> Does any coordinate or location data get embedded in the image
>>>>>>> file if I use Project > Save as Image or Composer > Export as
>>>>>>> Image/PDF/SVG?
>>>>>>>
>>>>>>> I'm using QGIS version 2.14.3 Essen, although I would like to know
>>>>>>> about more recent versions, too, for when I upgrade later.
>>>>>>>
>>>>>>> (I'm aware of the option to check "World file on" and create a
>>>>>>> separate world file. What I need is to make sure there is no
>>>>>>> identifying info whatsoever from the project file in the image
>>>>>>> file itself.)
>>>>>>>
>>>>>>> Eg, say I have a basemap like OpenStreetMap open for a country
>>>>>>> and I load points in another layer that are inside that country.
>>>>>>> Then I zoom in on a group of points from my data layer, I turn
>>>>>>> off the basemap layer, and make a map with just my data points. I
>>>>>>> want to preserve the relative spatial relationships between my
>>>>>>> points but not reveal where in the world the map came from. If I
>>>>>>> publish this image file, might the metadata reveal the location?
>>>>>>>
>>>>>>> For the work we do, it's critically important we not unknowingly
>>>>>>> publish specific locations.
>>>>>>>
>>>>>> AFAIK, if you save in PNG or JPEG format no coordinate
>>>>>> information is stored in metadata of the image:
>>>>>>
>>>>>> $ exiftool Inhambu.jpg
>>>>>> ExifTool Version Number : 10.80
>>>>>> File Name : Inhambu.jpg
>>>>>> Directory : .
>>>>>> File Size : 49 kB
>>>>>> File Modification Date/Time : 2019:06:01 11:37:04-03:00
>>>>>> File Access Date/Time : 2019:06:01 11:37:04-03:00
>>>>>> File Inode Change Date/Time : 2019:06:01 11:37:24-03:00
>>>>>> File Permissions : rw-r--r--
>>>>>> File Type : JPEG
>>>>>> File Type Extension : jpg
>>>>>> MIME Type : image/jpeg
>>>>>> JFIF Version : 1.01
>>>>>> Resolution Unit : inches
>>>>>> X Resolution : 96
>>>>>> Y Resolution : 96
>>>>>> Image Width : 917
>>>>>> Image Height : 665
>>>>>> Encoding Process : Baseline DCT, Huffman coding
>>>>>> Bits Per Sample : 8
>>>>>> Color Components : 3
>>>>>> Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2)
>>>>>> Image Size : 917x665
>>>>>> Megapixels : 0.610
>>>>>>
>>>>>> $ exiftool Inhambu.png
>>>>>> ExifTool Version Number : 10.80
>>>>>> File Name : Inhambu.png
>>>>>> Directory : .
>>>>>> File Size : 47 kB
>>>>>> File Modification Date/Time : 2019:06:01 11:37:04-03:00
>>>>>> File Access Date/Time : 2019:06:01 11:37:04-03:00
>>>>>> File Inode Change Date/Time : 2019:06:01 11:37:44-03:00
>>>>>> File Permissions : rw-r--r--
>>>>>> File Type : PNG
>>>>>> File Type Extension : png
>>>>>> MIME Type : image/png
>>>>>> Image Width : 954
>>>>>> Image Height : 652
>>>>>> Bit Depth : 8
>>>>>> Color Type : RGB with Alpha
>>>>>> Compression : Deflate/Inflate
>>>>>> Filter : Adaptive
>>>>>> Interlace : Noninterlaced
>>>>>> Significant Bits : 8 8 8 8
>>>>>> Pixels Per Unit X : 3780
>>>>>> Pixels Per Unit Y : 3780
>>>>>> Pixel Units : meters
>>>>>> Image Size : 954x652
>>>>>> Megapixels : 0.622
>>>>>>
>>>>>> If you save as geotiff the positioning information should be
>>>>>> written in metadata. I don't know about the PDF format. In any
>>>>>> case, all informations, except the CRS, will be written to the
>>>>>> world file.
>>>>>>
>>>>>> HTH
>>>>>>
>>>>>>
>>>>>>> Thank you, first time posting, very much appreciate QGIS and its
>>>>>>> community!
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Roxo
>>>>>>
>>>>>> --
>>>>>> ---------------- Non luctari, ludare -------------------+ WYSIWYG
>>>>>> Fernando M. Roxo da Motta <petro at roxo.org> | Editor?
>>>>>> Except where explicitly stated I speak on my own behalf.| VI !!
>>>>>> PU5RXO | I see
>>>>>> text, ------------ Quis custodiet ipsos custodes?-------------+ I
>>>>>> get text!
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>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Roxo
>>>
>>> --
>>> ---------------- Non luctari, ludare -------------------+ WYSIWYG
>>> Fernando M. Roxo da Motta <petro at roxo.org> | Editor?
>>> Except where explicitly stated I speak on my own behalf.| VI !!
>>> PU5RXO | I see text,
>>> ------------ Quis custodiet ipsos custodes?-------------+ I get text!
>>>
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--
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
RR # 1
Thorburn, NS
B0K 1W0
Tel (902) 922.3607
Email: kirk at nortekresources.com
Web: www.nortekresources.com
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