OpenSeaMap Seamark Sector Light values

Question:

I extracted the OSM XML node for a light house with sector lights to use for some graphics. However, the sector values do not make sense to me.

I found the attributes mentioned on several wiki pages:

• https://wiki.openstreetmap.org/wiki/Seamarks/Lights#Sectored_Light_Attributes
• https://wiki.openstreetmap.org/wiki/Seamarks/Sectored_and_Directional_Lights
• https://wiki.openstreetmap.org/wiki/Seamarks/Seamark_Attributes
• https://wiki.openstreetmap.org/wiki/Seamarks/Radar_Beacons
• https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dlighthouse

but none of these seems to specify the units or interpretation of the values.

The first example on https://wiki.openstreetmap.org/wiki/Seamarks/Sectored_and_Directional_Lights clearly shows the first sector directed to the north-east, while its values are:

seamark:light:1:sector_end=260
seamark:light:1:sector_start=230

The values are the heading in degrees, from a vessel. I was looking for the opposite angle...

Here's a Python snippet to convert the angles (you may be able to run this on an "online Python" service):

#!python3
#coding=utf-8
""" Invert OSM seamark sector headings (degrees as seen from light)"""
import sys,re
toggle = False
with open("OSM_node.xml") as f:
  for line in f:
    if "sector" in line:
        # get heading angle
        mo = re.search("'(\d+.\d)'", line)
        heading = float( mo.groups()[0] )
        # "invert" angle
        angle = heading - 180
        if angle < 0:
            angle = angle + 360

        # optional: flip angles > 180 degrees (for SolveSpace CAD)
        if angle > 180:
            angle = (angle - 360)

        # print value and add a blank line every other
        print( angle )
        if toggle:
            print()
        toggle = not toggle

# EOF

You are welcome to start submitting your question anonymously. After submiting your question, you will be redirected to the login/signup page. Your question will > be saved in the current session and will be published after you login with your existing account, or signup for a new account and validate your email.

is misleading (cannot submit anonymously) and did not work for me / question lost after registration.