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Create Transition Rates Table

Source: R/trans_rates_t.R
trans_rates_t.Rd

Creates a trans_rates_t table that stores transition rates for each transition type in each time period. For observed periods, rates describe the change that happened; for extrapolated periods, they prescribe the change allocation has to produce. Future rates can be extrapolated with a linear regression (extrapolate_trans_rates()) or derived from target class shares or areas with a linear program (solve_trans_rates()).

Usage

as_trans_rates_t(x)

get_obs_trans_rates(self)

extrapolate_trans_rates(obs_rates, periods, coord_count = NA_integer_)

# S3 method for class 'trans_rates_t'
print(x, nrow = 10, ...)

trans_rate_areas(lulc_data, rates, trans_meta)

Arguments

x

A list or data.frame coercible to a data.table

self

a DB instance

obs_rates

A trans_rates_t table of observed transition rates for historical periods

periods

A periods_t table with is_extrapolated = TRUE for future periods

coord_count

Optional integer specifying the number of coordinates (cells) for normalization

nrow

see data.table::print.data.table

...

passed to data.table::print.data.table

lulc_data

A lulc_data_t for a single id_run; the areas of its last period are the state the replay starts from.

rates

A trans_rates_t table for a single id_run.

trans_meta

A trans_meta_t table, resolving id_trans to a pair of classes.

Value

A data.table of class "trans_rates_t" with columns:

  • id_run: Foreign key to runs_t

  • id_period: Foreign key to periods_t

  • id_trans: Foreign key to trans_meta_t

  • count: Absolute number of transitioning cells for (id_trans, id_period)

  • rate: Transition rate: count of transitions in (id_trans, id_period) over count of cells of id_lulc_anterior in id_period

trans_rate_areas() returns a data.table with id_lulc, id_period and area; id_period is the period whose state the area describes, so the initial state carries the last period of lulc_data.

Methods (by generic)

  • print(trans_rates_t): Print a trans_rates_t object, passing params to data.table print

Functions

  • get_obs_trans_rates(): Calculate observed transition rates from historical data. For each period and transition type, calculates the rate as the proportion of id_lulc_anterior cells that transitioned to id_lulc_posterior.

  • extrapolate_trans_rates(): Return future transition rates using linear regression. For each id_run + id_trans, fits a linear model of rate vs period number and extrapolates to future periods. Negative predicted rates are set to 0.

  • trans_rate_areas(): Replay a rate table forward from an observed state to recover the class areas it implies. Transitions not recorded in rates are implied to be zero, so the residual 1 - sum(rate) of each class persists. This is what makes a solved trajectory recoverable from a trans_rates_t alone, and therefore comparable against the areas an allocation run actually realised.