Chapter 33

Precision Viticulture

Geographical Information System

A geographic information system (GIS) is really just a type of database system to manage large volumes of geo-coded spatial data derived from a variety of sources. The capabilities of GIS are to accept input data, to serve as a clearing house for data, to store, retrieve, manipulate, analyze, overlay, and display these data based on the requirements of the user and to create both tabular and cartographic output which reflect these requirements. Geographic data contains not only the attribute being reported but also the spatial location of the attribute. An example of an attribute would be the value of yield produced by a particular spot in the vineyard. In most GIS software data is organized in themes as data layers. This approach allows data to be input as separate themes (e.g., soil moisture, soil fertility, temperature, humidity, etc.) and overlaid based on analysis requirements. In addition to data storage and display, the GIS can be used to analyze characteristics between layers by combining and manipulating data layers to produce an analysis of management scenarios.

Characteristics of Maps

Maps provide a traditional method of storing, analyzing, and presenting spatial data. Reviewing how maps are produced is an important step in understanding their limitations for use in a GIS.

Data Formats

There are two categories of GIS data formats or structures: raster and vector (See Figure 33.6). The two formats are used to geo-code land data on the basis of whether the data type is composed of point, linear, or aerial features. Most resource data is aerial and is encoded in a defined area in raster or vector formats.

Vector Format

In the vector approach, the basic units for storing and displaying data are the points, lines, or polygons (areas) that create the terrain and objects on a map. The method represents data by simulating the geographical entities, much as if the points, lines, and shapes were being drawn on a map.

Raster Format

Raster model divides the entire study area into a regular grid of cells (similar to a spreadsheet layout) in specific sequence with each cell having a unique value (row and a column number) to represent the landscape. In this format, data are stored by assigning an attribute, or numerical value, to each cell. Raster data structures characterize continuous data (such as imagery) and are exceptionally strong where boundaries and point information are not well defined.

GIS Data Types

Attribute Data

The attributes refer to the properties of spatial entities. They are often referred to as non-spatial data since they do not in themselves represent location information.

Spatial Data

Geographic position refers to the fact that each feature has a location that must be specified in a unique way. To specify the position in an absolute way a coordinate system is used. For small areas, the simplest coordinate system is the regular square grid.

Coordinate Systems

All GIS software packages employ geo-referencing to organize spatial data. Geo-referencing basically means that every entry in a database is associated with a geographic location or coordinate on a map.

Local Coordinates

A local coordinate system may be all that is needed for a particular vineyard. Local coordinates are referenced to a known location in the area. For example, the southwest corner of the vineyard may be considered the (0,0) point, or origin, of the local coordinate system. All other points on the vineyard are represented by distances from this point.

Latitude/Longitude Coordinates

Latitude/Longitude coordinates are the only true geographic coordinates.

UTM Coordinates

UTM is a metric coordinate system commonly used for mapping at scales from 1:500,000 to 1:24,000. This rectangular coordinate system is based on a cylindrical projection of the same name, i.e., the Universal Transverse Mercator projection.

State Plane Coordinates

State plane coordinates (SPC) are not based on a single projection but instead divide all 50 states into 120 zones, which are represented by several projections based on the shape of the zone.

Using all Coordinate Systems

When a grower uses one of these three coordinate systems to locate points in a vineyard, anyone else using the same coordinate system can find the points on a map, given the coordinates. The important message is that we need the ability to quickly change from one coordinate system to another in many instances. For example, soil maps from the National Resources Conservation Service (NRCS) office in the U.S. normally contain state plane coordinates.

Methods Used to Analyze Precision Vineyard Data

When mapping second-by-second data from a yield monitor, smoothing techniques are used to help visualize trends.

Nearest Neighbor

Nearest neighbor interpolation is probably the simplest of the methods.

Local Average

Local average estimates the unknown values by a simple average of a selected number of points around the desired location.

Inverse Distance Weighting

Inverse distance weighting (IDW) is similar to local averaging except that samples closer to the unsampled location have more influence on the estimate than samples farther away. This method assumes that the unknown point is more likely to have a value similar to point closer to it than those farther away.

Contouring

Contouring is another method of interpolating data to generate maps. Contouring was originally developed to display elevation changes on a topographic map. Topographic maps display contour lines that connect points with the same elevation.

Kriging

Kriging (pronounced kreeging) is probably the most complex interpolation method being used in precision viticulture. Kriging has been shown to create very good interpolations of such things as soil properties when enough data are collected to use it properly. It follows two basic steps. First, an estimate is made of the variability that exists in the raw data.

Computer Hardware and Software

Typically GIS is used to refer only to the software used to analyze geographic data but a complete system includes hardware too since you canít use one without the other to perform GIS analysis. A complete GIS system usually contains the following hardware components:

Data Input

Before geographic data can be used in a GIS, the data must be converted into a suitable digital format. The process of converting data from paper maps or aerial photographs into computer files is called digitizing. Modern GIS technology can automate this process fully for large projects using scanning technology; smaller jobs may require some manual digitizing which requires the use of a digitizing table.

Primary Data Sources

The primary data sources can be entered to the GIS database in many ways. Indirect methods include recording the values in the vineyard manually on notebook and then entering them in the GIS software using a computer.

Secondary Data Sources

The secondary data are from other digital sources and they must be converted to the required format for the GIS.

PC Card

The most common method for loading the data into a GIS is through a PC card. The data may be written on a PC card in different formats. In order for the software to read the data it must be able to recognize the format.

Digitizing and Scanning Maps

Before geographic data can be used in a GIS, the data must be converted into a suitable digital format. The process of converting data from paper maps or aerial photographs into computer files is called digitizing. Modern GIS technology can automate this process fully for large projects using scanning technology; smaller jobs may require some manual digitizing which requires the use of a digitizing table.

Digitizing

The easiest, though not necessarily most precise, method of making electronic maps tends to be computer scanning. With a computer scanner, a user can copy, or scan, any image into the computer.

Scanning

The secondary data are from other digital sources and they must be converted to the required format for the GIS.

Data Manipulation and Analysis

GIS software performs a number of tasks, mainly geometric calculations, map-overlay computations, network analysis, and production of estimates of parameters for transfer to external analytical models; all through user-defined rules. Through various operations, this function enables the use of spatial and nonspatial data contained in the GIS database to perform what-if analysis.

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