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I am looking for QGIS function to extract (or detect) edge from a raster, which was referred in here, How to digitize a raster automatically as answer by @MappaGnosis.

The name could have changed since then, or it may have been integrated into other tool... I cannot find it in my QGIS Processing Toolbox (2.14.10 and 2.18.2).

There are similar tools such as GRASS "i.zc Zero-crossing" and SAGA "Gaussian filter", but I am hoping to find this QGIS geoalgorithm.

  • It seems that the link you provided refers to vector analysis: do you want a raster or a vector as output? – mgri Jan 13 '17 at 11:02
  • Yes, @HowToInQGIS, thank you for pointing that. What I want is to have the edge (or sharp change) as a vector (linestring). If the tool returns a raster, I think I can turn it to vector. So both cases would do for me. – Kazuhito Jan 13 '17 at 11:13
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    @Joseph Thank you so much! I had never installed Orfeo Toolbox, so it was a bit challenging... but it was worth trying. Now I can see so many Edge Extraction(s), including Sobel filter. Wow. – Kazuhito Jan 13 '17 at 11:41
  • @Kazuhito - Most welcome, glad it was helpful! Will post the comment as an answer for the convenience of others :) – Joseph Jan 13 '17 at 11:50
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The Edge Extraction tool may have been moved to the Orfeo Toolbox as this focuses on image analysis. The Orfeo Toolbox contains a number of edge extraction tools using various methods such as:

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