# Depth-depth curves and correlation

    library(admtools)

`admtools` comes with utilities to deal with depth-depth curves that are used for correlation between sections. See the developer documentation (`vignette("admtools_doc")`) for all available functionality.

### Constructing depth-depth curves

There are two ways to construct depth-depth curves: from coeval tie points or from age-depth models. To construct depth-depth curves from coeval tie points use `tp_to_ddc` (ddc stands for depth-depth curve).

    # simulation data
    # entries in vectors are coeval bc simulation time steps were identical
    h1 = CarboCATLite_data$height_2_km_offshore_m
    h2 = CarboCATLite_data$height_12_km_offshore_m
    ddc1 = tp_to_ddc(h1 = h1,
                     h2 = h2,
                     L_unit_1 = "m", # associate length units
                     L_unit_2 = "m",
                     sec_1 = "2 km offshore", # name of correlated sections
                     sec_2 = "12 km offshore")

Alternatively, you can use two age-depth models to construct depth-depth curves via `adm_to_ddc`. This will construct depth-depth curves for the overlapping time interval.

    adm_2km = tp_to_adm(t = CarboCATLite_data$time_myr,
                        h = CarboCATLite_data$height_2_km_offshore_m,
                        L_unit = "m",
                        T_unit = "Myr")

    adm_8km = tp_to_adm(t = CarboCATLite_data$time_myr,
                        h = CarboCATLite_data$height_8_km_offshore_m,
                        L_unit = "m",
                        T_unit = "Myr")

    ddc2 = adm_to_ddc(adm1 = adm_2km, adm2 = adm_8km)
    # assign section names
    ddc2 = set_section_names(ddc2, sec_names = c("2 km from shore", "8 km from shore"))

### Plotting and summaries

You can quickly plot depth-depth curves using `plot`:

    plot(ddc1,
         type = "l",
         xlab = "",
         ylab = "")
    mtext(get_section_names(ddc1)[1], side = 1, line = 3)
    mtext(get_section_names(ddc1)[2], side = 2, line = 3)

A quick overview of the contents is provided via `summary`:

    summary(ddc1)

    ## depth-depth curve between 2 km offshore and 12 km offshore
    ## Thickness of 2 km offshore : 146.0621 m
    ## Thickness of 12 km offshore : 16.51814 m

### Modification

Length units and section names can be extracted and modified using `get_L_units`, `set_L_units`, `get_section_names` and `set_section_names`. To reverse the direction of correlation, use `flip_ddc`:

    plot(ddc1, type = "l", xlab = "", ylab = "") # correlation from 2 km offshore to 12 km offshore
    mtext(get_section_names(ddc1)[1], side = 1, line = 3)
    mtext(get_section_names(ddc1)[2], side = 2, line = 3)

    ddc3 = flip_ddc(ddc1)
    plot(ddc3, type = "l", xlab = "", ylab = "") # correlates 12 km offshore with 2 km offshore
    mtext(get_section_names(ddc3)[1], side = 1, line = 3)
    mtext(get_section_names(ddc3)[2], side = 2, line = 3)

Note that this effectively flips the plot along the diagonal.