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I'm very new to QGIS and am having some issues using the SAGA IDW tool. I'm attempting to perform an interpolation using the 10 closest sample points and an inverse distance power of 2. I would like to specify a cell size of 5000 meters; however, the cell size appears to be much larger than 5000 meters on the output grid. What am I doing incorrectly?

  • The cell size is probably in decimal degrees, not meters. – csk Apr 5 '18 at 16:23
  • Ok, thank you! So I need to change the coordinate system of my point data to something other than wgs84? – Jen Apr 5 '18 at 16:27
  • Probably. Most tools use the units of the layer, but I couldn't find any documentation on how this tool chooses units. Start with changing the CRS of the point data; if that doesn't work try changing the project CRS and/or default units under project settings. – csk Apr 5 '18 at 16:40
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Your points are in EPSG 4326 which is WGS84, a global coordinate system in degrees. As @csk mentioned, it's 5,000 degrees and not meters. Your input data should be in a projected coordinate system. So you either need to project your data if it's in EPSG 4326 or change its coordinate system if the wrong one is attached.

  • Thank you @Techie_Gus! That was a really silly mistake; however I'm still having a similar issue now that all of my layers are projected in 102008 NA Albers Equal Area. I'm still getting warnings in the processing log about duplicate algorithms names and duplicate parameters. – Jen Apr 9 '18 at 1:21
  • These are my parameters Points: O3Albers Attribute: HI48HR Target Grid System: user defined Cellsize: 2500.000000 Left: -10142431.578633 Right: 3310068.421367 Bottom: -2070847.975523 Top: 4571652.024477 Fit: nodes Search Range: global Number of Points: maximum number of nearest points Maximum: 12 Direction: all directions Weighting Function: inverse distance to a power Inverse Distance Weighting Power: 2.000000 Inverse Distance Offset: no – Jen Apr 9 '18 at 1:21

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