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Data has been given to us in a HUGE .xyz file, which has been split into many component CSV files. When I upload the CSV file, then create the shape file by "save as", all is fine. When I go to Raster, then Interpolation, the resulting layer appears incomplete, as if it hasn't been processed. - Image below...

enter image description here

Question is: is it incomplete due to lack of "machine-power" (very doubtful) or data issue (doubtful, as it appears OK in the CSV) or is it a limitation of QGIS? Is there an easier way of uploading the enormous files rather than splitting them and risking a data error?

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    what are the parameters of your raster interpolation ? – gene Jul 24 '14 at 15:59
  • I have Eastings, Northings and water depth in metres - We're trying to characterise the seabed bathymetry. – stevepace Jul 25 '14 at 8:39
  • ok, but the parameters of the interpolation ? – gene Jul 25 '14 at 8:54
  • Sorry, don't understand the question... after adding the csv via "Add Delimited Text" and saving as a shape file, I go to Raster, Interpolation and select the vector (Shape) file, the interpolation attribute is the depth column, I click Add. I click "Set to Current Extents", choose where to put the output file, add the result to project and click OK. Could you identify where I would find the interpolation parameters? – stevepace Jul 28 '14 at 11:49
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Your data seems to be equally spaced, so I suggest to load it as a XYZ Raster file. You have to obey the expected sorting order: http://www.gdal.org/frmt_xyz.html

If qgis fails on the file size, try to do the conversion with pure GDAL. It gives better error messages, and saves the valuable RAM that the QGIS GUI needs.

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The regular pattern of the image makes me suspect that you have loaded the data incorrectly. I'm not sure how you loaded the CSVs. Assuming that each CSV is a three colum table with a header, I would try loading it using Layer→Add Delimited Text Layer. Make sure the result of this a point layer that displays as points with plausible water depths in the attribute table. If it is, test interpolation on this layer (which, incidentially, you can do without saving it to shapefile first).

If this doesn't work, some other clarifications would be helpful. In the order these operations would be performed:

  1. What does a snippet (first few lines) of the original file look like?
  2. Is each CSV just a horizontal partition of the original file? A snippet of one would be helpful here as well.
  3. How did you load the CSVs? I.e., did you just Add Vector Layer, or did you Add Delimited Text Layer?
  4. What does the point layer look like? I.e., an image of the input to the interpolation process, not just the result, would be helpful as well.
  • In reverse order... I added the layer as a delimited text layer, then saved as a shape file. I can't open the original file as it's too large for excel. However, here's the horizontally split file excerpt:313142.5 5857550.5 -4.31 313142.5 5857549.5 -4.3 313142.5 5857548.5 -4.3 313142.5 5857547.5 -4.31 – stevepace Jul 28 '14 at 11:38

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