Georeferencing of UAV photos

Revision as of 13:35, 19 April 2016

Preparation

1. Install the Openlayers plugin (if not yet done)

Template:Plugins - Manage and Install Plugins - Install

1. Activate the Georeferencer GDAL plugin (if not yet activated):

Template:Plugins - Manage and Install Plugins - Install Check the box beside the Georeferencer GDAL plugin.

1. Prepare the reference data

Right click on the main menu. Activate the Browser Panel by checking the box beside the Bowser panel Drag the Browser window that opens on top of the Layer window. Browse to your geodata folder where the tutorial data were stored and extracted. Mark geodata and right click 'Add as a favourite'. Browse to geodata\Goe\thematic\topo_utm32_WGS84.tif and load the topographic map 1:25.000 into the map viewer with a double click. Web OpenLayers Plugin Google Maps Google Satellite. The Project Coordinate system switches automatically to EPSG:3857 WGS 84 / Pseudo Mercator in the mode on the fly transformation. In the Layer Panel drag the Layer topo_utm32_WGS84 on top of Google Satellite. Double click on topo_utm32_WGS84 to open the Layer Properties Transparency and change Global transparency to about 70% by moving the slider. Apply. Browse to geodata\Goe\thematic\DJI00857.JPG and load a UAV photo into the map viewer with a double click. The Coordinate Reference System Selector opens. The UAV photo is a raw image file in JPEG fornmat which does not contain information on a spatial reference system. Just press ESC to load the image. Open Project Project Properties and check the box on the fly transformation off. Mark DJI00857 in the Layer panel and right click Zoom to Layer. Double click on DJI00857 in the Layer panel and change the band the band assignement in Layer properties Style to Red band: Band1, Green Band: Band 2 and Blue Band Band 3. The raw uav image is now shown as a true color composite. Especially striking are the lens distortions caused by the ultra-wide (fisheye) lens of the UAV camera. Load the geodata\Goe\thematic\DJI00857_entzerrt.tif in the map viewer. The lens distortion is minimized using calibration coefficient of a camera model. Open DJI00857_entzerrt.tif in the windows photo viewer and rotate the image such that it is correctly oriented to the north direction. Open Project Project Properties choose EPSG:3857 WGS 84 / Pseudo Mercator and check the box on the fly transformation on. Mark topo_utm32_WGS84 in the Layer panel and right click Zoom to Layer.

Registration of ground control points (GCP)

Opening the Georeferencer window: Template:Raster – Georeferencer – Georeferencer In the georeferencing window Template:File - Open raster Browse to your geodata folder. Template:Geodata\Goe\thematic\DJI00857 entzerrt.tif ((open)) Defining reference system with ESC (none) Change the band assignment to RGB = 1,2,3 with Settings - Raster Properties - Style. OK. Georeferencer Settings Configure Georeferencer check the box beside 'Show IDS'.

Template:Georeferencer - add point Template:Georeferencer - add point See sceenshot ´´Add_Point.jpg´´ A cross shows up. Move the cursor to the first ground control point (e.g. a drain cover). Zoom in and mark the GCP with the croos and register position in the image shown in the Georeferencer. Enter map coordinates : From map canvas. OK. Zoom in to the same point in Google maps. In the Layer panel switch topo_utm32_WGS84 on and off. Attention! if the zoom factor is too large the Google maps is not displayed or not on the correct position. The coordinates of the main viewer are transferred directly to the Enter map cordinates window. OK. Zoom to the next control point, activate add point and continue until you have registered 10 GCPs.

For changing the position of a point that is already defined: ((move GCP point)) (second button on the right of the ´´add point´´ button) Move the point by clicking on it.

Transformation

Raster Projections Warp (Reproject)

Quality Check