R/polar_to_XY.R

In mqueinnec/itcfuns: Functions to analyze stem-mapped and itc data

#' Polar to XY coordianates
#' Convert polar coordinates to cartesian coordinates. Used for example if trees were mapped form plot center using distance and azimuth
#' @param azimuth - Numeric vector of azimuth from plot center
#' @param distance - Numeric vector of distance from plot center
#' @param xcenter - Cartesian X coordinate of plot center
#' @param ycenter - Cartesian Y coordinate of plot center
#' @param azimuth_offset - Optional. If the tree is leaning and measurement was from plot center to the stem, azimuth between stem and tree top.
#' @param distance_offset - Optional. If the tree is leaning and measurement was from plot center to the stem, distance between stem and tree top.
#' @param shape_file - Optional
#' @param crs - Optional.
#' @export

azimuth <- stem_mapped_polar$Azimuth
distance <- stem_mapped_polar$Distance
xcenter <- stem_mapped_polar$XPLOT
ycenter <- stem_mapped_polar$YPLOT
azimuth_offset <- stem_mapped_polar$CrownOffsetAzimuth
distance_offset <- stem_mapped_polar$CrownOffsetDistance

polar_to_XY <- function(azimuth,
                      distance,
                      xcenter,
                      ycenter,
                      azimuth_offset,
                      distance_offset,
                      shape_file = TRUE,
                      crs) {
  #angle = azimuth - 90
  #angle[angle<0] <- 360 + angle[angle<0]
  if((max(azimuth) - min(azimuth) < 2*pi) == TRUE){
    print("WARNING: This function assumes azimuth is in degrees, please check")
  }
  angle = azimuth * pi/180
  #Convert to radians
  #angle = angle*pi/180
  angle = 2*pi - (angle - pi/2)
  x = xcenter + distance * cos(angle)
  y = ycenter + distance * sin(angle)

  # Apply offset
  if(!missing(azimuth_offset) & !missing(distance_offset)){
    angle_offset = azimuth_offset * pi/180
    angle_offset = 2*pi - (angle_offset - pi/2)

    x_offset = distance_offset * cos(angle_offset)
    y_offset = distance_offset * sin(angle_offset)
  }else{
    x_offset = 0
    y_offset = 0
  }
  
  #define output point locations
  tree_locations <- data.frame(X = x + x_offset, Y = y + y_offset)
  
  if(shape_file == T){# output a shape file of the tree locations
    print(paste("creating spatial points layer from tree locations. CRS is:", crs))
    
    tree_locations <- sf::st_as_sf(tree_locations, coords = c("X", 'Y'), crs = crs)
    
  }
  else{
    tree_locations
  }
  return(tree_locations)
}