If I understand correctly, in the Open() call, this driver would open
each image file to read its EXIF info and index the files in memory?
This would work fine with a dozen images, but as the number of images
increases the performance will suffer a lot and this would become
unusable in apps such as MapServer, and even for Desktop apps with
hundreds of images.
If I needed this kind of functionality myself I would use a script to
create an OGR point file as suggested by Even, to avoid the overhead
caused by opening all the images.
My 0.02$
Daniel
On 12-07-23 5:27 AM, Tamas Szekeres wrote:
Hi Even,
I just want to use the directory name to define the connection to the
images, we could also provide to scan the files in subdirectories if
needed. I would prefer to have a new driver not just an offline tool for
creating OGR datasets, in this case many existing applications (like
MapServer) would be capable to utilize this feature.
I could imagine a driver configuration file to specify which driver
should be used for a particular image format and where the specific
information is located, I don't require to harmonize the metadata
structure at this time. We should probably allow mixing jpegs and tiffs
in the same directory, but the configuration should specify how the
similar attributes are provided by each (sub)driver.
Best regards,
Tamas
2012/7/23 Even Rouault <[email protected]
<mailto:[email protected]>>
Le lundi 23 juillet 2012 09:51:14, Tamas Szekeres a écrit :
> Hi All,
>
> We're thinking about implementing a new OGR driver which would
represent a
> set of images as a vector data source. The images are taken from
any GPS
> compatible mobile device, and each picture would be represented
as a point
> feature, the positions would be extracted from the exif
information. The
> file name and path would be provided as an attribute for each
feature. This
> data source could then be used by higher level apps to provide
symbols at
> the picture locations in the map and display the picture when the
feature
> is selected. The driver would definitely use GDAL to extract
information
> about the provided images.
>
> I'm not sure whether we already have some kind of alternative
solution to
> this, let me know if you know about any. Further ideas about this
topic
> would also be helpful.
The JPEG driver already exposes EXIF information if found :
$ gdalinfo ../autotest/gdrivers/data/albania.jpg
Driver: JPEG/JPEG JFIF
Files: ../autotest/gdrivers/data/albania.jpg
Size is 361, 260
Coordinate System is `'
Metadata:
[...]
EXIF_GPSLatitude=(41) (1) (22.91)
EXIF_GPSLatitudeRef=N
EXIF_GPSLongitude=(19) (55) (42.35)
EXIF_GPSLongitudeRef=E
[...]
$ gdalinfo ../autotest/gcore/data/exif_and_gps.tif -mdd EXIF
Driver: GTiff/GeoTIFF
Files: ../autotest/gcore/data/exif_and_gps.tif
Size is 1, 1
Coordinate System is `'
[..]
Metadata (EXIF):
[...]
EXIF_GPSLatitude=(77) (5) (60)
EXIF_GPSLatitudeRef=S
EXIF_GPSLongitude=(34) (12) (0)
EXIF_GPSLongitudeRef=E
[..]
Are you thinking to other raster formats to extract EXIF info from?
To my
knowledge, the JPEG driver, and recently the GTiff driver, are the
only one
that extract EXIF for now. I see that the JPEG driver exposes it in the
default metadata domain, whereas I chose EXIF for the GTiff driver.
For GTiff,
the specific EXIF metadata domain seemed better to me to avoid
'polluting' the
default metadata domain, but I didn't want to change the JPEG driver
at that
point. But this would probably requires some harmonization.
So with some scripting, you could create for example a point
shapefile, with
the filename as attribute and GPS position as geometry.
In its syntax, this could be something similar to gdaltindex.
Doing that as a OGR driver would be also doable of course. The only
point to
solve is the definition of the connexion string to specify the image
set.
>
> Best regards,
>
> Tamas
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Daniel Morissette
http://www.mapgears.com/
Provider of Professional MapServer Support since 2000
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