# [OSM-dev] Develop a Simple Mapping Tool for Mobile Phones

Yarik Iaroslav.Sheptykin at hs-bremen.de
Thu Mar 24 12:19:10 GMT 2011

```Thanks, Nic!
I need time now to digest what you wrote.

On Thu, 2011-03-24 at 14:00 +0200, Nic Roets wrote:
> On Thu, Mar 24, 2011 at 12:08 PM, Yarik <Iaroslav.Sheptykin at hs-bremen.de> wrote:
> >        You have offered help in triangulation in one of the prev
> >        emails. A couple links would be awesome for a quick
> >        initialization. Thanks in advance!
>
> Firstly, sensors give you magnetism and gravity as 3D vectors. For
> every picture, obtain magnetic East (in the horizontal plane) you take
> the cross product of the two vectors. Then you get magnetic North by
> taking the cross product of magnetic East and gravity. Then you
> project the camera vector onto the horizontal plane to get the azimuth
> angle. Then get elevation angle with the cosine rule.
>
> When the user selects multiple photos aimed at the same point, you can
> estimate that point using some least squares method. Preferably the
> photos should have a large angular separation (as seen from the point
> being observed), otherwise the results will be inaccurate (in GPS, it
> is called Dilution Of Precision).
>
> All these terms are described on Wikipedia, but they focus on linear
> variables. Angles are non-linear. So either one should look at books
> or papers describing theodolite computations, or just make your own
> approximations and simulations. For example it may be sufficient to
> assume the Earth is flat after applying the equirectangular
> projection.
>
> >
> > Greets,
> > Yarik
> >
> >
> > On Wed, 2011-03-23 at 20:22 +0200, Nic Roets wrote:
> >> On Wed, Mar 23, 2011 at 5:30 PM, Yarik <Iaroslav.Sheptykin at hs-bremen.de> wrote:
> >> > Hi Nic!
> >> >
> >> >        Great to hear! I has been thinking of building a tool like that
> >> >        for quite a long time already with slightly different
> >> >        functionality than you describe but still very similar. I wrote
> >> >        already that I worked on location based mobile games. In many
> >> >        games players are encouraged to take pictures of different
> >> >        objects. The challenge I always faced in data analyzes was to
> >> >        extract any useful information out of those pics about features
> >> >        (landmarks in particular). You offer an interesting approach. Do
> >> >        you know anything about the last year SoC project? Would it make
> >> >        sense to extend its achievements?
> >>
> >> No, I haven't looked at it.
> >>
> >> >        Since you say such apps are useful for community, I will develop
> >> >        the idea further. I will also try to apply to SoC this year. But
> >> >        even in case I fail I would be interested in the development.
> >> >        Are you going to apply for SoC too / mentoring?
> >>
> >> I'm not going to apply for SoC.
> >>
> >> I'd be happy to informally mentor anyone developing software to
> >> process sensor and GPS data. I built up a little bit of experience
> >> with my KeypadMapper project, as well as porting Gosmore to Android.
> >>
> >> In the long term (i.e. not this year) it would be nice to detect logos
> >> (trademarks), perhaps do OCR or even photosynth type survey.
> >>
> >> But in the short term there is no image processing necessary. Simply
> >> show the user a crosshair. He can then take multiple "shots" of an
> >> object to collect it's height and location.
> >
> >
> >

```