The idea of the modeler for me is to save time and keep consistent processes. In the screen shot below you can see that the model requires the yield data point file (where the Dry Yield table column needs selecting), paddock boundary and the grid and filtered points output file location. The model takes care of all the processing steps.
While constructing the model the only tricky part was making sure I had a separate ‘Extent’ field to input into the ‘Shapes to Grid’ algorithm. Even though I always leave this blank, it is required for the algorithm to realise the extent is just the minimum covering extent of the input shape file.
A few years ago I used to use model builder in ArcGIS and really missed it when I no longer had access to ESRI software. The SEXTANTE Modeler fills that gap and allows a combination of algorithms from several different toolboxes.
Some more advanced applications of Sextante Modeler are available here.
The process to convert point data to raster (or grid) for can differ dramatically depending on who you ask and the purpose of the conversion. Generally data is processed for two main functions. The first being ‘stacking’ or ‘layering’ to later develop prescription maps or other further processing. The second is improved visual representation of the data. My process aims to satisfy both with minimal processing time. My method does contain some compromises; since I use a coarse resolution it is not as pleasing on the eye as some other methods. In addition, my data smoothing technique is quite broad which means you will loose some detail in the grid.
At this point in time I follow these steps:
Clean up point data either manually manually or with a filter to remove any obvious errors such as where header turns in paddock. EDIT: I am currently trying Yield Editor for this step.
Produce a grid over the top of the point data. Any cells that share a points average the point values.
Gaps in the grid are filled in.
Gaussian Filter is used to ‘smooth’ the data.
In QGIS this is the process:
Note: You will need to have SEXTANTE and additional toolboxes setup to follow these steps. Instructions are available here.
Load paddock boundary (shape file polygon)
Load yield data points (You will need these in shape file format – use export function in SMS or FOViewer if your yield monitor does not produce ESRI shape file)
QGIS rivals ArcGIS as desktop GIS software especially within Precision Agriculture. The difference is that QGIS is Open Source and therefore free to use for personal and commercial use. Open Source has many other advantages. If you are familiar with ArcGIS you should give QGIS a go.
If you run Windows I recommend installing using the OSGeo4W installer. Run the ‘Desktop Express Install’.
‘Out of the box’ QGIS is very capable. But it is not until you install a few powerful plugins that it’s real potential is revealed. So far the plugins I use on a daily basis are: SEXTANTE and Table Manager. SEXTANTE is not much good to me without SAGA. Together these make available a comprehensive list of common Vector and Raster GIS algorithms. Optionally install TauDEM and Orfeo (I have installed these but not yet used them).
Setting up SEXTANTE in QGIS 1.8 (Windows 7 & 8)
Install Sextante Plugin (In QGIS: Plugins > Fetch Python Plugins).
So SEXTANTE has access to the SAGA algorithms it needs to be downloaded and installed: SAGA.
Configure SAGA in SEXTANTE (In QGIS: Analysis > SEXTANTE options > SAGA), insert SAGA folder and check Activate box.
Similar to SAGA, download and install TauDEM 5.0.6 & MPICH2 (make sure you follow install instructions on the download page).
Configure TauDEM in SEXTANTE (In QGIS: Analysis > SEXTANTE options > TauDEM), insert MPICH2 bin directory, TauDEM command line tools folder and check Activate box.
Install Table Manager
Plugins > Fetch Python Plugins
Search for Table Manager and click Install.
With these two plugins, especially SEXTANTE, QGIS becomes extremely capable.