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I am using QGIS for analysis of aerial images.

I have used the properties>style menu to create colour-banding for my raster map layer. This created 2 colour bands - but I want to convert these to seperate vectors.

Is it possible to do this - and do I require a plugin?

See below for screen grab:

qgis vector raster conversion

histogram

code

legend

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  • Nope,yo need reclassify your raster using the raster calculator ans export the results using raster to vector for create polygons using only your classification.
    – Fran Raga
    Commented Nov 20, 2017 at 15:35

1 Answer 1

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In your case, reclassify your raster with the formula like below in the Raster Calculator : 

("Pistford_2_NGRDI_values@1" <= 0.14)*2 + ("Pistford_2_NGRDI_values@1" > 0.14)*1

It should look like below :

raster calculator

  • Then you can convert your integer raster to vector polygon :

Polygonize

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  • Thanks for the help! I have no programming knowledge - is there a straightforward expression for picking out everything that has a wavelength <-0.14? This is shown as yellow on the image.
    – Josh
    Commented Nov 20, 2017 at 15:51
  • Basically its: >0.14 = 1 and <0.14 = 2 - but I don't know the format to use. Thanks again
    – Josh
    Commented Nov 20, 2017 at 16:12
  • What about values = 0.14 ? I suppose it's <= 0.14 from your printscreen. For your case, I updated my answer with more info
    – gisnside
    Commented Nov 20, 2017 at 16:22
  • Ps : the band is specified by @1 or @2. Make sure your have the right band in the formula.
    – gisnside
    Commented Nov 20, 2017 at 16:28
  • Brilliant - thaniks for all your help - I'll have a go today and report back
    – Josh
    Commented Nov 22, 2017 at 9:10

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