GCP -> Post process cartography -> ODM + GCP -> QGIS

[balthazarneveu]

• [ ] Check feasability of using GCP
• [ ] Train @FlorinePepin on the subject.

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1. Single image in QGIS A. It is possible but it does not work correctly in QGIS directly ! . Please check #17 ! B. Alternatives
   • A tool worth mentioning https://github.com/OpenDroneMap/ODM/tree/master/contrib/orthorectify ... but it needs ODM to process many photos to reconstruct the ortho then it can orthorectify each single image ...
   • ideally we'd want altitude + fov from exif to place the photo correctly on the map. somewhat similar to https://gis.stackexchange.com/questions/384756/georeference-single-drone-image-from-exif-data

I recommend always fly and move the drone around. do not stay static so you can always feed ODM with multiple frames.

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2. Visible cartography

• why? up to date compare to google earth in MapInfo / QGIS .
• constraints = align accuracy ~50cm

Probably bad solutions: A: manual alignment or custom python alignment
B. test dji visible images from v1.2 in Mapinfo C. can we manually align in QGIS? -> using GCP (with GUI) in ODM , most probably yes! QGIS raster alignment?

Not the right way use GCP (ground control points) instead is what professional geometers do! see 3. :

• use a high end GPS + markers to be very accurate
• or use fake GCP to align into existing maps like google maps

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3. Accuracy

It seems that using GCP (ground control points) is the right thing to do. https://www.groundcontrolpoints.com/#:~:text=Ground%20Control%20Points%2C%20or%20GCPs,visible%20in%20these%20aerial%20photos. In the following blogpost GCP+Aruco from ODM , they're using Aruco to link

• super accurate locations from GPS
• to the actual pixel location on the images. Link to the github Find GCP

In webODM there's a GCP graphical interface to manually select corresponding points between the drone picture & the map

Using FAKE GCP pointed on the map may be a "good enough" workaround.

4. Usage

WebODM

[balthazarneveu]

Setting fake GCP ground control points blog article ... https://turfstuf.wordpress.com/2020/09/18/fake-ground-control-points-for-drone-mapping/

[AlainNeveu]

Paramétrage des options pour réaliser une orthophoto avec WebODM.

On suppose que l'on dispose des images d'une mission aérienne (appelée par exemple Mission-01) Les images du dossier .../Mission-01/AerialPhotography ont été alignée avec iRDrone et placées dans _.../Mission-01/mappingMULTI/images . Dans ce dossier est aussi présent la définition de la caméra _.../Mission-01/mapping_MULTI/cameras/cameraIRdrone.json .

** Ouvrir WEBODM
          > Tableau de bord 
          >  ajouter un projet
** Dans la fenêtre Nouveau projet > donner un nom ( ex. _Mission-01_) ainsi qu'une courte description (facultatif).
                                        > +Créer un projet 
** > Sélectionner des images ( .../Mission-01/mapping_MULTI/images/ Hyperlapse-0001-1.tif ... )
** puis dans la fenêtre   
    > Nom : (par défaut un numéro de tâche est attribué automatiquement)                        
    > Noeud de traitement :  _Auto_                         

    > Option > choisir "par défaut" > Dupliquer (avec la petite flèche à droite du bouton modifier) 
        Dans la fenêtre "Modifier les options de la tâche"
        - donner un nom : IRDrone
        - modifier les options
            * camera-lens : brown
            * > importer un fichier .json >  .../Mission-01/mapping_MULTI/cameras/camera_IRdrone.json
            * fast-orthophoto :  Activate
            * force-gps :  Activate
            * orthophoto-resolution** :  1  (cm/pixel)
            * primary-band :  Green
            * smrf-scalar :  1.3
            * smrf-threshold :  0.3
            * smrf-slope :  0.05
            * smrf-window :  24
            * texturing-skip-global-seam-leveling :  Activate
            * texturing-tone-mapping** :  gamma (or none)
            * use-exif** :  Activate
            * use-fixed-camera-params :  Activate
        > enregistrer

    > Valider.

La commande complète apparaît dans la fenêtre de la tâche.

_camera-lens: brown, cameras: {"irdrone multispectral 3892 2892 brown 0.75":{"projection_type":"brown","width":3892,"height":2892,"focal_x":0.75,"focal_y":0.75,"c_x":0,"cy":0,"k1":0,"k2":0,"p1":0,"p2":0,"k3":0}}, fast-orthophoto: true, force-gps: true, orthophoto-resolution: 1, skip-band-alignment: true, smrf-window: 23, texturing-skip-global-seam-leveling: true, use-exif: true, use-fixed-camera-params: true

> Lancer le traitement

Lors du prochain projet dans la liste déroulante de la commande Option, l'option IRDrone apparaîtra en plus des options standards.