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Support nautical mile unit in annotation_scale() function #137

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Support nautical mile unit in annotation_scale() function #137

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c6dc617
Add a "nautical" option to unit_category in GeomScaleBar()
ylbb5e Apr 12, 2026
8504b7b
Define unit selection for unit_category = "nautical" incl. "nmi"
ylbb5e Apr 12, 2026
8626434
Implement conversion between "nmi" and SI units
ylbb5e Apr 12, 2026
e1a0e91
Add "nmi" as a valid plot_unit value in GeomScaleBar()
ylbb5e Apr 12, 2026
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25 changes: 16 additions & 9 deletions R/annotation-scale.R
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@
#' Otherwise, just pass them as arguments to `annotation_scale`.
#' \itemize{
#' \item width_hint: The (suggested) proportion of the plot area which the scalebar should occupy.
#' \item unit_category: Use "metric" or "imperial" units.
#' \item unit_category: Use "metric", "imperial" or "nautical" units. The latter behaves like "metric" but use nautical miles ("nmi" units) instead of kilometers.
#' \item style: One of "bar" or "ticks"
#' \item location: Where to put the scale bar ("tl" for top left, etc.)
#' \item line_col and text_col: Line and text colour, respectively
Expand Down Expand Up @@ -125,8 +125,8 @@ GeomScaleBar <- ggplot2::ggproto(
line_col <- data$line_col[1]

stopifnot(
is.null(plot_unit) || plot_unit %in% c("mi", "ft", "in", "km", "m", "cm"),
length(unit_category) == 1, unit_category %in% c("metric", "imperial"),
is.null(plot_unit) || plot_unit %in% c("mi", "ft", "in", "km", "m", "cm", "nmi"),
length(unit_category) == 1, unit_category %in% c("metric", "imperial", "nautical"),
is.numeric(width_hint), length(width_hint) == 1,
is.atomic(bar_cols),
is.numeric(line_width), length(line_width) == 1,
Expand Down Expand Up @@ -286,7 +286,7 @@ scalebar_params <- function(
plotunit = NULL,
sf_crs = NULL,
widthhint = 0.25,
unitcategory = c("metric", "imperial")
unitcategory = c("metric", "imperial", "nautical")
) {
# params check
unitcategory <- match.arg(unitcategory)
Expand Down Expand Up @@ -323,7 +323,7 @@ scalebar_params <- function(
plotunit <- "m"
}

plotunit <- match.arg(plotunit, choices = c("km", "m", "cm", "mi", "ft", "in"))
plotunit <- match.arg(plotunit, choices = c("km", "m", "cm", "mi", "ft", "in", "nmi"))

heightm <- .tosi(sf_bbox["ymax"] - sf_bbox["ymin"], plotunit)
widthm <- unname(.tosi(sf_bbox["xmax"] - sf_bbox["xmin"], plotunit))
Expand All @@ -333,19 +333,22 @@ scalebar_params <- function(
geowidthm <- unname(widthm * widthhint)

if(geowidthm < 1) {
scaleunits <- c("cm", "in")
scaleunits <- c("cm", "in", "cm")
} else if(geowidthm < 1600) {
scaleunits <- c("m", "ft")
scaleunits <- c("m", "ft", "m")
} else {
scaleunits <- c("km", "mi")
scaleunits <- c("km", "mi", "nmi")
}

# String unit = units[unitCategory] ;
if(unitcategory == "metric") {
unit <- scaleunits[1]
} else {
} else if(unitcategory == "imperial") {
unit <- scaleunits[2]
} else {
unit <- scaleunits[3]
}

# double widthHintU = Units.fromSI(geoWidthM, unit) ;
widthhintu <- .fromsi(geowidthm, unit)
# double tenFactor = Math.floor(Math.log10(widthHintU)) ;
Expand Down Expand Up @@ -427,6 +430,8 @@ scalebar_params <- function(
sivalue * 39.370079999999809672
} else if(unit == "cm") {
sivalue * 100.0
} else if(unit == "nmi") {
sivalue / 1852
} else {
stop("Unrecognized unit: ", unit)
}
Expand All @@ -445,6 +450,8 @@ scalebar_params <- function(
unitvalue / 39.370079999999809672
} else if(unit == "cm") {
unitvalue / 100.0
} else if(unit == "nmi") {
unitvalue * 1852
} else {
stop("Unrecognized unit: ", unit)
}
Expand Down