[Qgis-user] Working with irregular magnetometry data points - converting them to an image

[Benjamin Ducke]

Hi Calvin,

On 20/04/18 18:46, Richard McDonnell wrote:
> Calvin,
> 
> Under Processing Toolbox, Type interpolation into the search bar, the
> tool you want can be found there.

None of the typical GIS interpolation tools will be
of much help here, since they have all been optimized
to work with relatively sparse data. They will be
too inefficient for high-resolution geomagnetic data.

You data is already dense, with some gaps. So you need
something that is fast and efficient for small
interpolation radii, and will not produce too many
artefacts.

If you can use the GRASS7 plug-in from within QGIS,
than this is a good processing path:

1. Rasterize your data points, using a cell size
small enough so that you don't have too much information
loss (i.e. not too many occurrences of more than one data
point per cell). This might take a little trial and error
to find good settings. You should end up with a raster
where you have gaps of max. 1-3 empty cells between cells
with measurement data.

Now you need to fill these relatively small gaps.

2. Use r.fill.stats from current GRASS 7.4:

https://grass.osgeo.org/grass74/manuals/r.fill.stats.html

... because that has been designed exactly for the
purpose. Set the interpolation radius as small as
possible, so that it just manages to fill the gaps.
With a small radius, r.fill.stats is very fast and
memory efficient, even on very large raster datasets.

Note that r.fill.stats is part of GRASS 7 only since
version 7.4. If your QGIS ships with an earlier
version, then you might have to update your GRASS 7
binaries manually.

Best,

Ben

> Regards,
> 
> Richard.
> 
> On 20/04/2018 16:42, C Hamilton wrote:
>> I don't know how many of you have worked with archaeological
>> magnetormetry data, but I have been asked to help with magnetometry
>> data of the ancient Mound Builders in North America. I am looking for
>> some suggestion on how to best turn the irregular magnetic data points
>> into an image.
>>
>> I see an Interpolation plugin that perhaps is the solution, but I also
>> see that it is not part of QGIS 3. Is this because it has not been
>> ported yet, or is not going to be porter, or is there a better solution?
>>
>> I don't know if any of the Lidar tools would work for this or not.
>> LASTools is a commercial product and the locked version only works
>> with small data sets and adds noise unless you purchase a license. At
>> least that is how it was the last time I used it.
>>
>> Thanks for any suggestions.
>>
>> Calvin
>>
>>
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> 
> -- 
> *_Richard McDonnell_*
> *GIS Specialist PgD GIS AssocSCSI*
> *OPW FRM Data Management*
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-- 
Dr. Benjamin Ducke
Deutsches Archäologisches Institut (DAI)
Zentrale Berlin, IT-Referat
* Projekt "Stunde Null" *