Calculating the inner angle
I have some polygons and I want to calculate the inner angle of each polygon. Now, I have the geometry of every line of polygons in the same attribute table as shown in the following image.
I want to calculate the inner angle using the following equation:
inner_angle= the bearing angle of the previous line - the bearing angle of the following line +180 (in degrees).
How can I write this in the code block in the model builder and do this for each polygon respectively?
Yes. The attached image just illustrates geometry table of points.
I just need code execute that :
_______________________________
for each polygon >>>>>>( Can the iterate feature in model builder do this loop ( for each polygon)?)
for i = 1: last line in the polygon
if i < the last line in the polygon
angle = the line bearing @ i - the line bearing @ (i+1) +180
if angle >360
angle= angle -360
end
if angle < 0
angle = angle +360
end
else
angle = the line bearing @ i - the line bearing @ first line
if angle >360
angle= angle -360
end
if angle < 0
angle = angle +360
end
end
end
_____________________________
The desired result as follow
I hope that I illustrated the problem clearly.
I would probably create a script tool that would be based on the following parameters:
- the featureclass
- the input polygon ID field
- the input line bearing field
- the "input" inner angle field (should exist or should be created by the tool) where the results will be written
- the same input featureclass as output parameter defined so you can connect the output to other tools in your model
The code would be something like this:
def main():
import arcpy
from collections import OrderedDict
# read parameters
fc = arcpy.GetParameterAsText(0) # r'C:\GeoNet\InnerAngle\data.gdb\angles'
fld_pol_id = arcpy.GetParameterAsText(1) # 'polygonID'
fld_bearing = arcpy.GetParameterAsText(2) # 'line_bearing'
fld_inner = arcpy.GetParameterAsText(3) # 'inner_angle'
# create a lst of the data
fld_oid = 'OID@'
flds = (fld_oid, fld_pol_id, fld_bearing)
dct_data = OrderedDict((r[0], [r[1], r[2]]) for r in arcpy.da.SearchCursor(fc, flds))
# create a list with polygon IDs
pol_ids = list(set([data[0] for oid, data in dct_data.items()]))
# process the polygons and store results in dct
dct_res = {}
for pol_id in pol_ids:
dct_bearing = OrderedDict((oid, data[1]) for oid, data in dct_data.items() if data[0] == pol_id)
lst_bearings = dct_bearing.values()
cnt = 0
for oid, bearing in dct_bearing.items():
if cnt == len(lst_bearings)-1:
inner_angle = lst_bearings[cnt] - lst_bearings[0] + 180
else:
inner_angle = lst_bearings[cnt] - lst_bearings[cnt+1] + 180
if inner_angle > 360:
inner_angle -= 360
if inner_angle < 0:
inner_angle += 360
dct_res[oid] = inner_angle
cnt += 1
# update the fc with the results
flds = (fld_oid, fld_inner)
with arcpy.da.UpdateCursor(fc, flds) as curs:
for row in curs:
oid = row[0]
if oid in dct_res:
row[1] = dct_res[oid]
curs.updateRow(row)
# set output
arcpy.SetParameterAsText(4, fc)
if __name__ == '__main__':
main()
This is what a test generated:
The reason that this will not be possible using a simple feature iteration is that when writing the current feature the line bearing of the next feature must be known.
hmmm, fun stuff ... modified hexagons, which followed the (n-2)*180 rule
Curious as to what you are using this for? A convexity index?
:----------------------------------------------------------------------
:Angle report....
....
.... snip ....
....
(2) number of angles... (7)
:array points...
[[ 300025.98 5000035. ]
[ 300034.96 5000033.03]
[ 300043.3 5000035. ]
[ 300043.3 5000025. ]
[ 300034.64 5000020. ]
[ 300025.98 5000025. ]
[ 300025.98 5000035. ]]
:interior angles [ 77.61 154.32 76.71 120. 120. 120. ]
:sum interior... 668.641029246
