GRASS GIS Manual: v.transect.kia

NAME

v.transect.kia

DESCRIPTION

v.transect.kia.sh calculates Kilometric Abundance Indexes (KIA) from a point vector representing sightings along a survey transect and a line vector representing transect paths. Both vectors are usually recorded in the field using a GPS.
Basically, a KIA is evaluated as

KIA = sum(objects recorded along transect) / transect length

NOTES

v.transect.kia.sh needs sqlite as a database backend. Make sure that your GRASS installation has been compiled with sqlite support. If the current database connection already uses sqlite, the existing connection will be used. On the contrary, a temporary sqlite connection will be created and used. Previous non-sqlite database connection will be restored at script end.

Both paths and waypoints maps must contain in their attribute table a field with the same name and type (idfield), containing transect unique identifiers. This field will be used to assign each waypoint to the transect along which it has been recorded. Automatic assignment e.g. based on the nearest transect will be implemented in the future,

Weighted KIA

In case of different kinds of signs, e.g. accounting for different number of individuals and/or different importance in defining a species' presence, waypoints can be diversified by adding a type field and using it with a weight table. In this case a weighted KIA will be calculated as:

KIA = sum(object recorded along transect * object type weight) / transect length

A weight table is a plain ASCII text file containing weight definitions, one per row, formatted as type code( type code...) = weight.
Two special cases are possible, i.e. use N or Q (uppercase!) as weights: if weight = N, values contained in the cluster size field nfield will be used as weights (and a field name present in the waypoints map must be specified as value for the nfield parameter). If weight = Q will be used, nfield must be supplied as well, and four classes, weighting respectively 1, 2, 3, and 4 will be automatically constructed, grouping nfield values by quartiles.
A sample weight table could be as follows:

A CO I P PE S U = 1
C = Q

I.e., waypoints of type A, CO, I, P, PE, S and U will count "1", whereas C type waypoint will be count as 1, 2, 3,or 4 after a reclassification of nfield values into quartiles.

Stratified KIA

It is often needed to calculate "partial" KIAs, splitting each path by habitat types or elevation ranges (e.g. to check whether any differences in abundance exist on different habitat types or at different elevations). This is achieved supplying a polygon vector that classifies the area covered by paths. The program assumes that the GRASS vector map specified as groups parameter contains a field (either numeric or textual) named class with class codes for each polygon. If the field has a different name, use the class parameter.

If stratified KIAs are calculated, be warned that the process is significantly longer than other KIA calculations, since v.overlay has to be called repeatedly to break each path. It is known that v.overlay is slow, and even if called appropriately in couple with v.select or setting a region as small as possible, calculation time could increase appreciably.

3D correction

In the case of transect in montane areas, the effective path length could be underestimated and should be corrected by draping paths on a digital elevation model. This is achieved using the elev parameter and supplying a DEM at a siutable resolution. The DEM must be prepared in advance.

EXAMPLES

Calculate plain KIA

A shapefile will be procuced, containing KIA values, directly from waypoints and tracks shapefile downloaded from a GPS unit.

v.transect.kia -s paths=tracks.shp waypoints=wypts.shp output=kia.shp

KIA by elevation ranges, 3D corrected

Paths will be split based on a vector derived from a DEM (with r.reclass plus r.to.vect), which classifies the study area into 200 m wide elevation ranges.

v.transect.kia paths=tracks waypoints=sightings output=kia-200m elev=srtm90 groups=elev200m class=height

AUTHOR

Clara Tattoni, Laboratorio di Ecologia, Dipartimento di Ingegneria Civile ed Ambientale, Università degli studi di Trento, Italy
Damiano G. Preatoni, Dipartimento Ambiente-Salute-Sicurezza, Università degli Studi dell'Insubria, Varese, Italy

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