Using QGIS 3.8.0 Processing > Toolbox > SAGA > Raster tools > Mosaic raster layers, I do not understand the purpose of the Match and Fit parameters.

Here's a screenshot of the Match parameter, with its none and regression options:

enter image description here

Here's a screenshot of the Fit parameter, with its nodes and cells options:

enter image description here

Neither the QGIS nor the SAGA documentation describes the purpose of these parameters and their options. Likewise, an internet search on the topic also turns up empty.

I've experimented with changing the various options, but I haven't found any resulting difference in the output - it is as if the options have no effect.


What is the purpose of the Match and Fit parameters?


When this tools runs, the output log states that it is SAGA Version: 2.3.2 (64 bit)

1 Answer 1


According to this forum

The match option performs a linear regression (based on the values of all overlapping cells) in order to fit the values of the grid in process to those that have already been added to the mosaic.

From my personal experience, the Fit option, allow you to center the pixel on the center of the cells or to one of its corners (can't remember which)

  • Thanks! I understand the individual words of the Match forum, but the intended message still eludes me (perhaps an example with screenshots would work better for me!). Regarding the Fit option, I'm curious why I would want to center the output on anything other than the input centers? Wouldn't centering the output on the input corner result in a shift of up to half a cell? I've always taken pains to assure that all my rasters (input and output) are snapped so that they are all identically aligned, so the idea of shifting makes me kinda queasy...
    – Stu Smith
    Commented Jul 23, 2019 at 18:24
  • 1
    Further testing has shown that using the Match > Regression options makes a sizeable difference compared to the Match > None option. However, since the inner workings of the Regression option aren't that clear to me, I can't tell what its results are really indicating.
    – Stu Smith
    Commented Jul 23, 2019 at 18:30
  • 1
    Further cogitation regarding the Fit > Nodes parameter: I've always understood nodes to be a vector construct, not raster. So why use vector terminology ("nodes") in a raster tool? Puzzling...
    – Stu Smith
    Commented Jul 23, 2019 at 18:41

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