[Geo4All] Need help -- Unsupervised classification in QGIS of a non-georeferenced aerial photo?

[Lene Fischer]

Hi
I made this workflow – a bit out of the original question – but found it fun to do  - (Like Saturday eve jigsaw puzzle)

How to count seagulls.

Workflow:

Open some sort of background – eg. OSM – Remember to have your CRS correct
Add your images to a folder
Use plugin Import Photos. This gives you the position of the image.

I estimated the area for the photo – Used the measure line for the ‘setup’.
Georeferenced the 4 corners and added the images (Raster>georeference)

Create a temp scratch layer as a mask for the area with seagulls.
Clip raster by mask layer

Change the image symbology from rgb to singleband grey
In Rasctercalculator find rasterband at 1>=130 change col and row with divide by 4 – if I use original pixelsize the next step will have too many polygons.

Rasterpixel to polygon or polygonise

Select Expression find field ‘Value’ or DN = 0 (depends which finction you use for raster to polygons).  Delete selected
Buffer 0.01 Dissolve
Multipart to single part
Find features smaller than a seagull--> delete
Find larger polygons (eg. Plastic)
Count polygons

In your image 463 seaguls.
Happy counting. In this way your student learn to manually do the tricks – and might do it in Modelbuilder too ;-)



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Regards

Lene Fischer
Associate Professor

University of Copenhagen
Department of Geoscience and Natural Resource Management
Forest and Landscape College
Nødebovej 77a
3480 Fredensborg
Denmark


MOB +45 40115084
lfi at ign.ku.dk<mailto:lfi at ign.ku.dk>


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Fra: GeoForAll [mailto:geoforall-bounces at lists.osgeo.org] På vegne af Charlie Schweik
Sendt: 23. februar 2019 13:52
Til: OsGeo, GeoForAll
Emne: [Geo4All] Need help -- Unsupervised classification in QGIS of a non-georeferenced aerial photo?

Hi GeoForAll colleagues,

I'm trying to generate an unsupervised classifcation of a single aerial photo taken by a quadcopter of gulls in a water body. I'm trying to count the gulls.
The image is in X/Y Cartesian coordinates -- it is not georeferenced. I'm trying to use QGIS' Semi-automated classification plug-in.
I can't get it to work because the image isn't in a geographic or projected coordinate system.

Does anyone have any ideas on how I could do this in QGIS?

Thanks in advance,

Charlie Schweik


--
Charlie Schweik
Professor
Department of Environmental Conservation & School of Public Policy
University of Massachusetts, Amherst

Facebook: Charles.Schweik
Twitter: @cschweik

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