Gravillons tutorial

2016-12-04T12:24:22Z

Barbero-Garcia : Minor corrections of the code

[[Image:picto-liste.png|25px|link=Tutorials]] [[Tutorials|Tutorials index]]
==Description==
During this tutorial, we will approach general concepts, basics tools and how to process an image dataset with overlapping with MicMac. This dataset is willingly light (4 images) to focus under MicMac tools rapidly.
This tutorial is designed specially for MicMac debutant with a light photogrammetry background.

==Download==
*You can find this dataset at :<code>http://logiciels.ign.fr/?Telechargement,20</code><br>Datasets are available at the bottom of the page, in part test datasets. Then, UnZip the ".zip" archive.

*There is also a direct link to download it in zip format here : <code>http://micmac.ensg.eu/data/gravillons_dataset.zip</code>

==Presentation==
This dataset was created by L.Girod at the University of Oslo, Norway. This dataset was acquired to model a volcano model created by O.Galland.
File present in the directory are :
*4 images : 1.JPG, 2.JPG, 3.JPG, 4.JPG.
[[Image:01_gravillons_caroussel.png]]
*GCPs coordinates : Dico-Appuis.xml.
*Mesure of GCPs in images : Mesure-Appuis.xml.
*1 Mask : 1_Masq.tif/1_Masq.xml
*2 commands scripts : gravillons.sh (Linux) et gravillons.bat (Windows)

==Tutorial==

===1 Tie-Points search===
The first step of each MicMac pipline is to look for tie points (points that are seen in more than one image), this step is call image matching and performed by the command [[Tapioca]] :
<pre>mm3d Tapioca All ".*.JPG" 1500</pre>
The All option is used here because we know that all the images are going to have tie points with each other (they all depict the same area).

<div class="toccolours mw-collapsible mw-collapsed" style="background-color: Lavender">
<h6 style="font-family: Helvetica:font-size: 40px">Go further</h6>
<div class="mw-collapsible-content">To process tie points at full resolution, use "-1" (instead of 1500 here):
<pre>mm3d Tapioca All ".*.JPG" -1</pre>
</div>
</div>

===2 Internal Orientation+Relative Orientation===
Photogrammetry is composed of three steps :
*Internal Orientation : which consist to determine camera's paremeter (focal length, PPA, PPS, distorsion center, or distorsion parameters).
*Relative Orientation : which consist to determine position of each camera's from each other in an arbitrary system.
*Absolute Orientation : which consist to bascule the relative orientation to a scaled and oriented system (typically WGS84)
In digital photogrammetry, the two first steps are generally processed at the same time. In MicMac, the tools which perform internal and relative orientation is call [[Tapas]] :
<pre>mm3d Tapas FraserBasic ".*.JPG" Out=Arbitrary</pre>
This tools use a compensation by least squares to determine camera's parameter and relative orientation. The option "FraserBasic", correspond to a model of distorsion for our camera. The "option" Out specify the name of the orientation directory (here it will be Ori-Arbitrary).

===3 Visualize Relative Orientation===
[[Image:01_Gravillonn_RO.jpg|thumb|250px||alt=Relative Orientation|Meshlab visualization]]
MicMac include a tools which create a sparse point clouds (TPs) for visualization. This tool is [[AperiCloud]] :
<pre>mm3d AperiCloud ".*.JPG" Arbitrary</pre>
After this step, a ".ply" file will appear in your working directory, open it with Meshlab (Screenshot 1 : see [[Install|Useful softwares for MicMac]])

===4 Absolute Orientation===
[[Image:01_Gravillonn_AO.jpg|thumb|250px||alt=Absolute Orientation|Absolute Orientation]]
For this datasets, Ground Control Points, are already measured in images (file "Mesure-Appuis.xml"). With 3 points (X,Y,Z) we can determine the 3D transformation between the arbitrary system (Relative Orientation) and the georeferenced system, this operation is call "Bascule" and can be performed by the command [[GCPBascule]] :
<pre>mm3d GCPBascule ".*.JPG" Arbitrary Ground_Init Dico-Appuis.xml Mesure-Appuis.xml</pre>
This tool process a first Bascule only with the GCPs (Directory Ori-Ground_Init), we will now calculate a second Bascule with GCPs and TPs. To do that, we use the command [[Campari]] :
<pre>mm3d Campari ".*.JPG" Ground_Init Ground</pre>
The new orientation is stocked in the directory "Ori-Ground". We can visualize it with [[AperiCloud]] :
<pre>mm3d AperiCloud ".*.JPG" Ground</pre>
You can visualize the points cloud created in Meshlab.

<div class="toccolours mw-collapsible mw-collapsed" style="background-color: Lavender;width: 1400px">
<h6 style="font-family: Helvetica:font-size: 40px">Go further</h6>
<div class="mw-collapsible-content">The file "Mesure-Appuis.xml" is already provided in the dataset, it contain the measurements of each GCPs in image coordinates (px). If you want to mesure the GCPs by yourself, you can use the tool [[SaisieAppuisInitQT]] before GCPBascule etc...
<pre>mm3d SaisieAppuisInitQT ".*.JPG" Arbitrary Dico-Appuis.xml Mesure-Appuis.xml</pre>
It launch a GUI to click on GCPs, when it's finish don't forget to save before leaving. It will create to files :
*Mesure-Appuis-S2D.xml : Measurements of GCPs in images coordinates.
*Mesure-Appuis-S3D.xml : Measurements of GCPs in Relative Orientation (here "Arbitrary"). Warning no unit.
So for the following command don't forget to use "Mesure-Appuis-S2D.xml" instead of "Mesure-Appuis.xml".

This command is best explained in the [[Pierrerue_tutorial|Pierrerue tutorial]].
</div>
</div>

===5 Create a depth map===
[[Image:01_Gravillonn_3DC.jpg|thumb|250px|3D Points Cloud]]
With any orientation directory, you can compute a depth map. The method consisting on using all the images to create a 3D model is call dense correlation or densification. In MicMac, it's performed by the command [[Malt]] :
<pre>mm3d Malt GeomImage ".*.JPG" Ground Master="1.JPG" ZoomF=2</pre>

===6 Create a Dense Points Cloud===
This last tool doesn't create directly a 3D point cloud. To generate it, you have to run an other tools, Nuage2Ply :
<pre>mm3d Nuage2Ply "MM-Malt-Img-1/NuageImProf_STD-MALT_Etape_7.xml" Attr="1.JPG" Out=1.ply RatioAttrCarte=2</pre>
Then visualize the 3D model "1.ply" in Meshlab.

===Conclusion===
With this tutorial, you went through a complete photogrammetric process with MicMac. This first tutorial was willingly easy and on a minimal dataset to help you kickstart your MicMac skills. To go further, try the next tutorials.

MicMac - Contributions de l’utilisateur [fr]

Gravillons tutorial