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lutraconsulting / serval

QGIS plugin for setting raster pixel values
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Accuracy Issues when combining Serval Plugin & QGIS' Extraction #31

Closed SvSz closed 3 years ago

SvSz commented 3 years ago

I really like the plugin! It adds such an important tool to the free ware GIS opportunity !

But I have some troubles with the accuracy of masks i created. Hopefully you can help:

orig This is my original image

linecover I drew some random "scratches" in form of polygons for my purposes

maskedjpg With the Button "Create Selection from Layer" and then choosing a high value before "Apply Value for selection" change the values of the raster to 10000 (a high, or bright value).

masks Clip Raster by Mask Layer... Input Layer: Raster; Mask Layer: aimed Polygon; Layer Output: Temporal Raster

masks3 Halo-Effect masks4 Only the layer that was changed with Serval. No Corona. White Area is bigger than the area from "Extraction"

This is the result in comparison. I made the mask_layer above transparent so the underlying pixels become visible, creating a "corona"-effect or halo-effect

masks5

here is another halo-effect example.

This shows, that Serval created more pixels around a polygon than QGIS' Extraction Tool.

I hope this problem is properly explained. I need the extend of the extraction from QGIS and the Painting from Serval to be exactly (!) the same.

Can you help?

Regards SvSz

SvSz commented 3 years ago

i could delete the problem if wanted. i solved the problem by useing the raster calc instead of extraction!

Cheers!

erpas commented 3 years ago

Hi Sv Sz,

Try to change the selection creation mode, as described here: https://github.com/lutraconsulting/serval/blob/master/Serval/docs/user_manual.md#selection-modes [image: image.png] If you turn in off it would only select cells that have their centroid in the selection polygon.

czw., 22 kwi 2021 o 20:41 Sv Sz @.***> napisał(a):

i could delete the problem if wanted. i solved the problem by useing the raster calc instead of extraction!

Cheers!

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