I've got 12 delimited text csv files with regular pseudo-gridded points for temperature and salinity which look like this when zoomed in (inc distances) and this when zoomed out. I'm trying to convert them to a smooth surface layer - assumedly interpolated - but using the interpolation plugin on a vector layer saved from one of the csv's produced this kind of output, irrespective of how many columns I use.

Please can someone suggest the best method to turn my grids of dots into a nice smooth surface that I can use colour interpolation on?

Many thanks in advance. I feel that this should be really simple but I'm bashing my head against it and keep failing! Cheers.

  • out of interest, why is it that the colour interpolation option isn't available for point data (such as these)? – dez93_2000 Jul 5 '13 at 16:05
  • what tool are you using and with what values? – Alexandre Neto Jul 5 '13 at 22:10
  • qgis interpolate raster; values for which variable? I set size to current extent & columns I've tried 300, 600, 1000, 1500. Cheers – dez93_2000 Jul 6 '13 at 7:38
  • In Interpolation plugin, you ca use one of two methods, IDW or TIN, try IDW, and if needed configure the p distance coeficient (in the tool icon) – Alexandre Neto Jul 6 '13 at 13:07
  • Thanks Alexandre, that's starting to look like what I want. I don't suppose you know offhand how one can fix the problem whereby trench bottoms are assumed to be higher - not guessed lower - than the last contour, and the opposite for beach line contours, where it guesses down (rather than zero)? – dez93_2000 Jul 7 '13 at 13:34

If you have a regular point grid, you can use Raster | Conversion | Rasterize to create a raster with exactly the attribute values of the input points converted onto raster values. No interpolation or other manipulation of attribute/raster values is applied.

  • Thanks, I'll do so. Re: the pseudo-gridded comment, if it's mostly a grid but has some non-uniform elements, one can also add Voronoi polygons and spatially join the csv values as per: gis.stackexchange.com/questions/83522/… – dez93_2000 Jan 20 '14 at 13:41

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