update readme [no chk]

Author: ctoney

README.Rmd

@@ -47,7 +47,9 @@ pak::pak("firelab/FIAstemmap")
 
 ### Predict tree crown width
 
-The data frame `cw_coef` contains a curated set of linear regression coefficients for predicting crown width from stem diameter of tree species in the conterminous US (see `?cw_coef`). The method for crown width prediction attempts to avoid extrapolation beyond the range of the model fitting data by providing reasonable fall backs for the obvious cases. Details are given in the documentation for `calc_crwidth()`. The input is a data frame of tree records which must have columns `SPCD` (FIA species code), `STATUSCD` (FIA tree status code, `1` = live) and `DIA` (FIA tree diameter). The `plantation` dataset used here is an example tree list included in the package.
+The data frame `cw_coef` contains a curated set of linear regression coefficients for predicting crown width from stem diameter of tree species in the conterminous US (see `?cw_coef`). The method for crown width prediction attempts to avoid extrapolation beyond the range of the model fitting data by providing reasonable fall backs for the obvious cases. Details are given in the documentation for `calc_crwidth()`. The input is a data frame of tree records which must have columns `SPCD` (FIA species code), `STATUSCD` (FIA tree status code, `1` = live) and `DIA` (FIA tree diameter). FIA distribute data using US customary units with `DIA` given in inches, tree height in feet, etc. Convenience functions are provided for converting to and from SI units (`in_to_cm()`, `cm_to_in()`, `ft_to_m()`, `m_to_ft()`).
+
+The `plantation` dataset used here is an example tree list included in the package.
 
 ```{r predict-crwidth}
 library(FIAstemmap)
@@ -57,7 +59,7 @@ library(FIAstemmap)
 head(cw_coef)
 
 # Add a column of predicted crown widths to the `plantation` tree list.
-# `within()` modifies a copy of the example dataset.
+# The base R function `within()` modifies a copy of the example dataset.
 tree_list <- within(plantation, CRWIDTH <- calc_crwidth(plantation))
 str(tree_list)
 ```
@@ -101,13 +103,18 @@ The `western_redcedar` dataset is another example tree list included in the pack
 
 ```{r spatstat-explore-cont}
 ## Spatial point pattern for the western redcedar tree list.
+
+# Give stem distances in meters.
+trees <- within(western_redcedar, DIST <- ft_to_m(DIST))
+
+X <- create_fia_ppp(trees, linear_unit = "m")
 X <- create_fia_ppp(western_redcedar)
 summary(X)
 
 plot(X, pch = 16, background = "#fdf6e3",
      main = "Western redcedar point pattern")
 
-K <- spatstat.explore::Kest(X, rmax = 12, correction = "isotropic")
+K <- spatstat.explore::Kest(X, rmax = ft_to_m(12), correction = "isotropic")
 
 plot(K, main = "Ripley's K for the western redcedar FIA plot")
 ```

README.md

@@ -68,8 +68,13 @@ model fitting data by providing reasonable fall backs for the obvious
 cases. Details are given in the documentation for `calc_crwidth()`. The
 input is a data frame of tree records which must have columns `SPCD`
 (FIA species code), `STATUSCD` (FIA tree status code, `1` = live) and
-`DIA` (FIA tree diameter). The `plantation` dataset used here is an
-example tree list included in the package.
+`DIA` (FIA tree diameter). FIA distribute data using US customary units
+with `DIA` given in inches, tree height in feet, etc. Convenience
+functions are provided for converting to and from SI units
+(`in_to_cm()`, `cm_to_in()`, `ft_to_m()`, `m_to_ft()`).
+
+The `plantation` dataset used here is an example tree list included in
+the package.
 
 ``` r
 library(FIAstemmap)
@@ -86,7 +91,7 @@ head(cw_coef)
 #> 6   ABMA   20 California red fir      <NA> 6.67 0.43  0.00 Gill et al. (2000)
 
 # Add a column of predicted crown widths to the `plantation` tree list.
-# `within()` modifies a copy of the example dataset.
+# The base R function `within()` modifies a copy of the example dataset.
 tree_list <- within(plantation, CRWIDTH <- calc_crwidth(plantation))
 str(tree_list)
 #> 'data.frame':    91 obs. of  13 variables:
@@ -189,6 +194,11 @@ the package.
 
 ``` r
 ## Spatial point pattern for the western redcedar tree list.
+
+# Give stem distances in meters.
+trees <- within(western_redcedar, DIST <- ft_to_m(DIST))
+
+X <- create_fia_ppp(trees, linear_unit = "m")
 X <- create_fia_ppp(western_redcedar)
 summary(X)
 #> Planar point pattern:  24 points
@@ -217,7 +227,7 @@ plot(X, pch = 16, background = "#fdf6e3",
 
 ``` r
 
-K <- spatstat.explore::Kest(X, rmax = 12, correction = "isotropic")
+K <- spatstat.explore::Kest(X, rmax = ft_to_m(12), correction = "isotropic")
 
 plot(K, main = "Ripley's K for the western redcedar FIA plot")
 ```