A SfM-based interface created for the assessment of transversal gully geometry

FreeXSapp has been developed as a freely-available interface for the assessment of gully XSs using the Structure-from-Motion (SfM) approach i.e. 3-D reconstruction of a scenery from images taken by non-calibrated cameras in a convergent way.

FreeXSapp is a stand-alone graphical user interface (GUI) written in Matlab code and comprises algorithms developed by the authors, a number of previous scripts written by other authors, as well as external calls to freely available SfM software such as Micmac and PMVS2. The current FreeXSapp version works for 32 and 64 bits computers on Windows systems.


Main window FreeXSapp

Intuitive interface

FreeXSapp was designed to be friendly and easy-to-use software.

System color code example

System color code

FreeXSapp have a color code for warning and next step information.

Input photography window Info windows

Multiple options windows

Exclusive windows for each options to simplify your work. In addition, FreeXSapp shows information about the processes like model precission, execution times, settings...

Pole and ArUco markers method

Two scaling and orientation methodology

The operator can either use a simple pole for manually picking its extremes on the interface (a. semi-automated approach) or two ArUco markers attached to a pole (b. fully automated).

manual input example

Automatic and Manual system

The user can combine automatic and manual system (blue and red points) for better results

Results image


FreeXSapp display a plan view of the DEM with the XS selected and the XS profile with XS dimensions (width, depth and area)


User information in FreeXSapp Manual. Technical information is available in the paper "Accurate 2D assessment of gully erosion using the photogrammetric interface FreeXSapp".

FreeXSapp paper and FreeXSapp manual available soon


FreeXSapp Windows version

FreeXSapp Windows 64 bits package:

FreeXSapp Windows 32 bits package:

ArUco Markers

Available ArUco Markers images:


  • Please read the principal references before use this software


FreeXSapp benefits from the work of the following previous developers:

1. Micmac by the IGN (under CeCILL-B license)

Several Micmac executables are included in the FreeXSapp package, the free photo-reconstruction software application by the IGN.

  • Website:
  • References:
    Deseilligny MP, Clery I. 2011. Apero, an Open Source Bundle Adjusment Software for Automatic Calibration and Orientation of Set of Images. In 4th Isprs International Workshop 3d-Arch 2011: 3d Virtual Reconstruction and Visualization of Complex Architectures , Remondino F and ElHakim S (eds). Copernicus Gesellschaft Mbh: Gottingen; 269–276.

2. PMVS2 by Furukawa and Ponce (under GNU General Public License)

PMVS is a multi-view stereo software that takes a set of images and camera parameters, then reconstructs 3D structure of an object or a scene visible in the images.

  • Website:
  • References:
    Furukawa Y, Ponce J. 2010. Accurate, Dense, and Robust Multiview Stereopsis. Ieee Transactions on Pattern Analysis and Machine Intelligence 32 : 1362–1376. DOI: 10.1109/TPAMI.2009.161

3. ArUco by Garrido-Jurado et al. (under BSD 2-clause "Simplified" License)

ArUco is a minimal library for Augmented Reality applications based on OpenCV

  • Website:
  • References:
    Garrido-Jurado S, Munoz-Salinas R, Madrid-Cuevas FJ, Marin-Jimenez MJ. 2014. Automatic generation and detection of highly reliable fiducial markers under occlusion. Pattern Recognition 47 : 2280–2292. DOI: 10.1016/j.patcog.2014.01.005
    Garrido-Jurado S, Munoz-Salinas R, Madrid-Cuevas FJ, Medina-Carnicer R. 2016. Generation of fiducial marker dictionaries using Mixed Integer Linear Programming. Pattern Recognition 51 : 481–491. DOI: 10.1016/j.patcog.2015.09.023

4. uigetfolder2 by Chris Cannell

Matlab script for directory selection dialog box which remembers the last directory selected.

5. Plane fit by Adrien Leygue

Matlab script for Fits a plane to a set of data points by minimizing the normal quadratic distance

6. Splash screen by Ben Tordoff

Matlab script for showing a splash-screen during MATLAB application start-up.