path: root/README

gipfel
======

Description
-----------
__gipfel__ helps to find the names of mountains or points of interest
on a picture.
It uses a database containing names and GPS data. With the given viewpoint
(the point from which the picture was taken) and two known mountains
on the picture, gipfel can compute all parameters needed to compute the
positions of other mountains on the picture.
gipfel can also be used to play around with the parameters manually. But be
warned: It is pretty difficult to find the right parameters for a given
picture manually.  
You can think of gipfel as a georeferencing software for arbitrary images
(not only satelite images or maps).  
gipfel also has an image stitching mode, which allows to generate
panorama images from multiple images that have been referenced with gipfel.
The nice thing about image stitching is that it reuses the code that
already exists for referencing images.  
gipfel uses the non-linear
[least squares method](http://en.wikipedia.org/wiki/Least_squares) to
compute the viewing paramteres from the given data points.

Requirements
------------
* fltk-1.1.x <http://www.fltk.org>
* libtiff <http://www.remotesensing.org/libtiff/>
* libjpeg <http://www.ijg.org/>
* exif utility <http://libexif.sourceforge.net/>
* GSL - GNU Scientific Library <http://www.gnu.org/software/gsl/>
* gipfel works on UNIX-like systems (e.g. Linux, *BSD and probably others)

Installation
------------
Unpack the tar file and run `./configure; make; make install`

Running
-------
To start gipfel, enter 

	gipfel <image>

where <image> is the actual picture in JPEG format.

You should now see a control window and the actual picture.
Additionally a "Choose Viewpoint" window should pop up, where you can search
for the viewpoint from which the picture was taken. Select a viewpoint and 
click "Ok".
Alternatively, you can enter the GPS coordinate of the viewpoint directly in
the control window.  
You can now use the controls in the control window to modify the view
parameters. These are:
* View direction
* Nick angle
* Tilt angle
* Focal Length
* Visibility

Play around with these parameters, until you see the names of 
mountains, which you already recognize on the picture.
Now middle-click on the small cross at the left of the name to mark it.
It should turn red. Now you can drag it with the left mouse button pressed
to the position of the mountain on the picture.
If you have positioned at least two mountains, you can click on
the "comp" button in the control window to compute the
parameters of the picture.

You may also want to have a look at the screen video at
<http://www.ecademix.com/JohannesHofmann/gipfel.avi>
for an example session.

Data File
---------
As stated before, gipfel needs GPS input data. The input data must be
an ASCII file with one line per mountain / point of interest.
Each line must contain the following values separated by a comma:

	<SHORTNAME>,<NAME>,<DESCRIPTION>,<LATITUDE>,<LONGITUDE>,<HEIGHT>

<SHORTNAME> and <DESCRIPTION> may be left empty.

The following line is a valid example:
	SMTSBG,Simetsberg,,47.56617,11.25358,1836

Fortunately, there is a great website <http://www.alpin-koordinaten.de>,
where you can download a suitable file containg quite a lot of data mostly 
concerning the alps:
Click on the "Suchen" button and the click on the diskette symbol below
the first table then select "Fugawi 3 TXT" format and click on "Download".

Obviously you can easily add your own entries to the data file or add them
to the database at <http://www.alpin-koordinaten.de>.

Thanks to the kind permission of the creators of
<http://www.alpin-koordinaten.de>, the standard gipfel tarball includes
a default datafile generated by <http://www.alpin-koordinaten.de>.

GPS Tracks
----------
Once you have determined the right parameters using the procedure described
above, you can load GPS tracks and display them on the picture. Use the
File->Load Track menu item. GPS tracks should be text files containing
one line per waypoint. Each line should be of the form:

<LATITUDE>,<LONGITUDE>,<HEIGHT>

GPS tracks are displayed with variable width depending on the distance 
of the way points from the current view point and the scale value. 
You can also modify the width using the "Track Width" slider.

Loading and Saving Images
-------------------------
gipfel allows to save the image paramters in the comment section of 
the JPEG image. Use the File->Save Image menu item. 
Note, that in the saved image all previous JPEG comments are removed.
If you open an image containing gipfel image parameters, they are 
automatcally set.

Hidden Object Detection
-----------------------
gipfel tries to identify objects in its database, that are hidden by others.
This is done by assuming that every object/peak has the form of a cone 
with a fixed steapness. If such imaginary cone would hide the view to a
point in the database, gipfel marks it as hidden. Hidden objects are
not shown by default, but you can enable the display of hidden objects using
the Option->Show Hidden menu entry. Hidden objects and hidden GPS way points
are displayed in blue.

Refraction
----------
Refraction caused by temperature and density gardients in the atmosphere is
taken into account according to the approximation described by Tom Chester in:
<http://tchester.org/sgm/analysis/peaks/refraction_calculation.html>
under the assumption of a temperature change of 6.5°C per 1000m and a
temperature T0 at view point level of 10°C.

Exif Data
---------
gipfel tries to get useful information from the exif data of the
input image. It uses the "Focal Length in 35mm Film" and the 
"GPS Longitude", "GPS Latitude", and "GPS Height" parameters, if they
exist.

Lens Distortion
---------------
Typical lenses especially wide-angle lenses diverge from the optimal
rectilinear projection.
gipfel can now partly correct the resulting errors.
To this end gipfel uses a standard distortion model with three parameters 
(k0, k1, and x0). Depending on these values, the distance d of an image
point from the center is modified by (k0 * d + k1 * d ^ 2).
x0 is the main point offset in X direction.  

If you mark and position more than 3 mountains on an image, gipfel
tries to correct lens distortion. You can see that the flags turn
green in this case.
Once you have reasonable values for k0 and k1 for a special camera and
focal length you can save the distortion profile (Distortion/Save Profile).
Whenever you now open an image taken with this camera model and focal
length, gipfel will use this distortion profile.
The distortion profiles are stored in the 
	$HOME/.fltk/Johannes.HofmannATgmx.de/gipfel
directory and can also be edited manually.
Independent of the distortion profiles one can also modify the
distortion parameters per image.
Distortion correction is also used when stitching panorama images.

Stitching Panorama Images
-------------------------
If you have multiple images from the same viewpoint referenced with gipfel
you can stitch them together to form a panorama image.
For stitching the input images must all have been correctly referenced
with gipfel and saved (see "Loading and Saving Images").
You can then call
        gipfel -s <img1> <img2> ...
to see the result in a window. Alternatively you can call
        gipfel -s -j <outimg> <img1> <img2> ...
to save the result as a JPEG image to <outimg> or
        gipfel -s -t <outdir> <img1> <img2> ...
to save the result as multiple TIFF images to directory <outdir>.
Use the multiple TIFF option for blending the result with enblend
<http://enblend.sourceforge.net/>.
The width and height of the result images can be adjusted with the
-w and -h options.
You can use the -b switch to enable bicubic interpolation, which
gives smoother results but is a bit slower.  

gipfel simply scans all directions needed for the panorama and determines
where these directions would end up on the various pictures. It can then
record the corresponding color values from the input images.  

In contrast to other stitching programs, the input images don't need to
overlap.

If you want to open a stitched image in gipfel to locate the mountains
on it, don't forget to choose Panoramic Projection!

Troubleshooting
---------------
* Obviously gipfel can only be as good as its input data. If there is no 
  data about the mountains on your picture, you are out of luck...
  But as the data file format is pretty simple and GPS receivers are common, 
  you can build up your own datafile.
* gipfel only works with full normal unmodified pictures taken with a 
  non-distorting standard objektive. If you have a panorama picture, you
  might want to try the "Panoramic Projection" support which 
  imlements a cylindrical projection (see "Projection" menu).
* I don't know, whether gipfel currently works correctly on pictures taken on
  the southern hemisphere, but I would appreciate any feedback about it.

Acknowledgements
----------------
Thanks to the guys from <http://www.alpin-koordinaten.de> for their public
GPS database. 
Also have look at their other site <http://www.alpen-panoramen.de>.
In newer versions I use maxima <http://maxima.sourceforge.net/> for
symbolic computation and code generation.
I also want to thank my brother Martin for his suggestions and the
discussions.

DISCLAIMER
----------
gipfel must __not__ be used for real navigation. You should not rely on the 
results of gipfel.

Johannes Hofmann, <Johannes.Hofmann@gmx.de>