Planning a Soil Sampling Field Visit using your GPS

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When you are planning a field visit for soil sampling using a GPS device, a number of aspects shall be considered to assure that it's efficient and useful. In this guidelines we'll review what things should be considered when planning the field visit, GPS settings, as well as GPS models and standards supported by GeoAgro GIS.

Considerations when planning a field visit

There are some considerations that should be taken into account when planning a directed sampling:

  • Create a layer with the proper data structure and define the sampling points.
  • Assign names/numbers to the sampling points.
  • Use symbology to differentiate sampling points.
  • Print out a map with sampling points to guide the person who will carry out the sampling.

Create a layer with the proper data structure and define the sampling points

It's important to create a layer with the proper data structure, since once the layer is created, the data structure cannot be modified. For this purpose:C

  1. Create a new vector layer
  2. Name the layer, define to which group it will belong, and choose a structure such as Soil Sampling, GPS Points or a similar structure
  3. Make another layer visible as a reference to define where you'll locate the samplilng points (for instance, it could be a productivity, yields, or soils layer).
  4. Select the layer created in step 1.
  5. Add sampling points using the tool Add an object

Assign numbers/names to the sampling points

Once you have defined the sampling points, it's important to assign them with numbers/names so they can later be found in the GPS screen; for this purpose:

  1. Select the sampling point/s, by using one of the Selection tools(for instance, using the tool selection by rectangle)
  2. Assign a number/nameto each of the sampling points using the tool Edit attribute data of selected objects. The number/name of the samplling point can be stored in the  column 'Sample' (if the structure is Sampling Lab Results) or in the column 'Point' (if the layer structure is GPS Points)


Sampling layer with the structure Sampling Lab Results


Sampling layer with the structure GPS Points

Differentiate sampling points using simbology

Once the sampling points have been placed and a number/name has been assigned, it's possible to label them with the assigned name, as well as differentiate them from other sampling layers


For this Purpose:

  1. Click on the tool Edit cartogaphy and layer properties
  2. Click on the Symbology Tab
  3. In the labelsection, choose the column with the points number/name (Column 'Sample' if the structure is Sampling Lab Results, or column 'Point' if the layer structure is GPS Points)


  1. To locate the label, in the LabelSection, click on the option[More Options].


  1. The options for locating labels are:
    Position: allows to define the label location
    Angle: allows to define an angle for label placement
    Separator: If the label shows more than one attribute, this option allows to define which caracter is used for separating them.
    Duplicates: If checked, duplicate labels will be shown.
    Overlap: It places labels to avoid overlaps. It's recommended to check it.
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  2. Using the options Fill and Border you can change the symbology of sampling points and differentiate them from other layers.

Print a map with sampling points for the person who will do the sampling

It's useful to print a map to guide the person who will do the soil sampling, using the Print tool. You can choose the 'Coordinates' option in the Print tool, to display samplijng points coordinates in the printout.


Considerations when using the GPS

This is a list of considerations to take into account when using your GPS:

  • 'Configuration of the GPS reference system: 'GeoAgro GIS works in the WGS 84 reference system (geographic coordinates), so the GPS Navigator must be configured to use this reference system. For more information please review this article://put link to article in english - Cómo configurar el sistema de referencias del GPS?.

  • Determine accuracy: it's important to take into account the GPS accuracy when you mark a waypoint, track or route, since it can have wide variations, and the imported points using the GPS Module//add link Módulo GPS, the data may be displaced when importing it into your farm map.

  • Clean the GPS frequently: GPS devices have limited storage for waypoints, tracks or routes; thus it's convenient to download waypoints, tracks or routes to layers in a GIS project, using the GPS module toolbar //add '''link barra de herramienta and then delete them from the GPS memory.

  • GPS with Serial connection vs USB: if your GPS navigator has a Serial connection and your notebook doesn't have Serial connection ports (only has USB ports), you will need to obtain a Serial to USB adapter and then install the corresponding driver so Windows can recognize it. For more information you may review this article: //add link Cómo conectar el GPS a la computadora?.

  • Where can I get the GPS driver?: when you buy the Serial to USB adapter, it should have the driver included. In case that you don't have that driver, you may be able to download it from this article, //add link Cómo instalar el driver del cable Serial a USB? , from where you may also find a step by step guide to install it.

GPS standards and models supported by GeoAgro GIS

link to FAQ on this topic

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