Sunday, March 23, 2008

Geotag photography with n810

In preparation to my trip to Nepal, I'd like to share with you experiments I've conducted in the previous weeks regarding GPS in n810 (thanks Nokia for selecting me in Maemo developer program, BTW) and geotagging photos.

First, some comments about GPS in n810 :

  • it is a good way to learn some things about GPS technology (thanks to Wikipedia) when you want to understand why it is taking so long to get a position fix. And then, you start to speak about sky search (take about 12 minutes to download satellites constellation rough positions for your position, called almanac, valid for several weeks), cold fix (take about 6 minutes to download satellite precise position, called ephemeris, only valid 4 hours) and warm fix (take about 30s, when ephemeris is still valid in the device).
  • Of course, there is no way to easy way to guess what kind of search n810 is doing when starting GPS. For the first time you use it in a geographical area, you can expect to wait for about 20 minutes. If you didn't get a GPS fix in the last 4 hours, you can expect a fix between 5 to 10 minutes. If you got a fix in the last 4 hours, you can get a fix in 30s to 1 minute (it is not impossible, I've been able to get such fast hotfix in a moving bus in Paris ;)
  • You should really install Maemo-Mapper. Preinstalled software (called Maps) is a stripped version of Navicore. Unfortunately, it is barely usable, since its main goal is to see license for full version. Its main feature is using vectoral maps (so you get France maps for about 300MB) and being able to do address search offline. It is quite funny to discover it uses ogg vorbis audio files, despite no "official" support for Ogg Vorbis in IT2008 from Nokia. OTOH, Maemo Mapper, after preloading maps from either OpenStreetmap, Google, Yahoo or Virtual Earth, is way more powerful : you can easily record tracks, way points, import POI (with help of gpsbabel, you get virtually import any GPS data into Maemo Mapper).
My first experiment was done in Brussels during FOSDEM in February. I spent an entire day walking and photographing in Brussels, with GPS tracking enabled (with Maemo-Mapper) on my n810. It worked fine with a full charge (about 7h of tracking) but the initial fix was quite slow to get (it was my first real experience with GPS, I learned a lot about it after FOSDEM). You take a photo of n810 displaying GPS time (to record time offset between camera and GPS) and then, you can start shooting and keep Maemo-Mapper in tracking mode. A nice addition to Maemo-Mapper would add a "low consumption" mode (ie no maps nor tracks drawing) but if you disable "auto-center","display track" and "show GPS details", you can get something decent.

Then, back at home, after developing Raw photos (using Ufraw), I geotagged them, using gpscorrelate and gpx track from Maemo-Mapper and pushed photos to Flickr. Et voilà : they are available on Flickr, with geo data. I've noticed a Geotag extension for F-Spot is being developed so I hope to be able to use it for my next batch of photos.


  1. Some interesting stuff at


  2. I have a very stupid question: why are you geotagging your JPG and not the RAW files? Apparently it's not possible to do it on RAW, i tried with Digikam. I find this a pity, as you need to geotag the same photo several times if you process several jpg. It just doesn't make sense. It should be in the RAW, as it's an information related to the original shot, and not about any processed jpg version. It should also follow in the tags of the JPGs. Can someone explain me this choice?

  3. Thanks philn, I've also tested gps_saver but I kind of prefer Maemo-Mapper : more functionalites and you have the same power consumption.

    François :
    by definition, RAW files are read-only, because their are in proprietary format (I'm not talking about DNG format, since there is still no way to convert a RAW file to DNG without any information loss), so you can't attach any kind of geotag to them.

    With gps_correlate, you can give a entire session of photos (ie after your developed them from RAW to JPEG) and geotag them in one action.

  4. Thanks Frederic. It's clearer to me now. I can just see that we cannot do it for bad reasons (proprietary format...). It's still possible to change some meta data in a RAW file (like the dates and times), it is possible thanks to some reverse engineering of the RAW format? And is it too optimistic to hope for the same possility for geotagging?

  5. No, François, there is no utility providing write support on RAW file. Some tools (like Digikam) can save additional metadata in an supplementary file in XMP format (if your file is named img_0101.cr2 for Canon, additional metadata will be saved in img_0101.xmp). This allows to easily export metadata which are often only available in photo software database.

    And remember you can't do anything with RAW files "directly", you will need to develop them either to JPG, PNG or TIFF.

  6. with Exiftool, you can modify your RAW file. I don't know if it's very reliable, but I had to adjust the date and time of dozens of RAW photos because my cam was set to the wrong date. I did it directly on the .cr2 with this tool, and it's working quite well. So maybe it's possible to use it to modify the geotags also. Geotag seems to be able to do it:

    I really hate to have to repeat the same thing for each different jpg version I process, that's why i'm trying to find a way to geotag my RAWs once for all. So maybe there is hope for a reliable geotagging of Raw files? At least CR2, that's all I would ask for...

  7. Thanks for the info, but I'm still think it is best to let raw files untouched and store those changes elsewhere. I don't understand why you need to repeat your changes on each jpeg versions : once you did the change on the first version, it will be available on derived versions.

    I didn't test Geotag before. I've checked it quickly and it is quite nice, with integration with Google Maps. BTW, it didn't seem to handle CR2 files.

  8. I know it's rare, but sometimes I process several versions of a same raw: a black and white version for instance, and a color version. Also, I can't consider myself as a good photograph, neither a advanced user of raw softwares. So I know that in a couple of months or years, I will probably reprocessed some raws. So it's quite annoying for me to include a geotagging in a JPG. I wouldn't mind to put the geotagging in a side file, but it's suboptimal to me. But it's just my point of view of course.

    About Geotag, the website states that it can write to CR2. But it probably requires to install the needed dependencies?

  9. You could also upload your tracks to OpenStreetMap even if you don't do any mapping yourself.

  10. Interesting thoughts. I hope to geo-tag photos from my next trips too.

    Oh, and I think this should be cross-referenced at as well!

  11. I don't see the point in uploading random (ie obtained in a photo shoot session) "by foot" tracks to OpenStreetMap, since they can't be useful to anybody to create maps.