How to execute a function and save in a new csv file? - python-3.x

Question

This program converts coordinates. What I am trying to do is to
use a csv file as input
use the function to convert the coordinates
save the output as a new csv file.
My file (worksheet.csv) has three columns, latitude, longitude and height.
How would I approach this?
import math
import csv
# semi-major axis of earth
a = 6378137.0
# 1/f is reciprocal of flatteing
f= 0.00335281068
# converts the input from degree to radians
latitude = math.radians(float(input('Enter Latitude:')))
longitude = math.radians(float(input('Enter Longitude:')))
height = float(input('Enter Height:'))
def earthConverter(latitude, longitude, height):
e = math.sqrt((2 * f) - (f**2))
N = a / math.sqrt(1-e**2 * math.sin(latitude)**2)
x = (N + height) * math.cos(latitude) * math.cos(longitude)
y = (N + height) * math.cos(latitude) * math.sin(longitude)
z = (N * (1 - e**2 ) + height) * math.sin(latitude)
return x, y, z
############################################
with open('worksheet.csv', 'r') as csvFile:
reader = csv.reader(csvFile)
for row in reader:
writer = csv.writer(csvFile)
writer.writerow(row[0], row[1], row[2], earthConverter(math.radians(float(row[0])),
earthConverter(math.radians(float(row[1])), earthConverter(float(row[2])) )
csvFile.close()

Answer 1

You've very close, but there are several things that need to be changed. Here's what I think is a full solution, but below I'll work through each part of the code
import math
import csv
def earthConverter(latitude, longitude, height):
f = 0.00335281068
a = 6378137.0
e = math.sqrt((2 * f) - (f**2))
N = a / math.sqrt(1-e**2 * math.sin(latitude)**2)
x = (N + height) * math.cos(latitude) * math.cos(longitude)
y = (N + height) * math.cos(latitude) * math.sin(longitude)
z = (N * (1 - e**2 ) + height) * math.sin(latitude)
return x, y, z
with open('worksheet.csv', 'r') as Infile, open('worksheet_out.csv', 'w') as Outfile:
reader = csv.reader(Infile)
# next(reader, None)
writer = csv.writer(Outfile)
for row in reader:
lat = math.radians(float(row[0]))
lon = math.radians(float(row[1]))
ht = math.radians(float(row[2]))
x, y, z = earthConverter(lat, lon, ht)
row_out = [row[0], row[1], row[2], x, y, z]
writer.writerow(row_out)
First, you can move the definitions of f and a into the earthConverter function itself to avoid any possible problems with variable scoping. This isn't strictly necessary.
Second, you can get rid of the latitude = math.radians(float(input('Enter Latitude:'))) lines. Those ask for user input, which is not what you want here.
Third, you cannot write back to the same csv. You've opened it in read mode ('r'), but even if you changed that, this post gives some details about why that won't work/is a bad idea. You can also get rid of the separate call to close the csv at the end of your code -- the with open() construction takes care of that for you.
Fourth, your earthConverter function returns a tuple, so you need to unpack those values somehow before trying to write them out again.
Everything in the for row in reader: block could be condensed into fewer rows. I broke it up this way because it makes it a little easier to read.
Also, you didn't mention whether your input csv had a header. If it does, then uncomment the line next(reader, None), which will skip the header. If you need to write a header out again, then you could change the for row in reader: block to this:
for i, row in enumerate(reader):
if i == 1:
header_out = ['lat', 'lon', 'ht', 'x', 'y', 'z'] # or whatever
writer.writerow(header_out)
lat = math.radians(float(row[0]))
lon = math.radians(float(row[1]))
ht = math.radians(float(row[2]))
x, y, z = earthConverter(lat, lon, ht)
row_out = [row[0], row[1], row[2], x, y, z]
writer.writerow(row_out)

Answer 2

All you have to do is create a Dataframe to read the csv file and create a for loop to iterate through each row so and insert it into a new Dataframe. Then we let the panda library Export it into a new csv file.
import pandas as pd
import math
# semi-major axis of earth
a = 6378137.0
# 1/f is reciprocal of flatteing
f = 0.00335281068
def earthConverter(latitude, longitude, height):
e = math.sqrt((2 * f) - (f**2))
N = a / math.sqrt(1-e**2 * math.sin(latitude)**2)
x = (N + height) * math.cos(latitude) * math.cos(longitude)
y = (N + height) * math.cos(latitude) * math.sin(longitude)
z = (N * (1 - e**2 ) + height) * math.sin(latitude)
return x, y, z
def new_csv(input_file, output_file):
df = pd.read_csv(input_file)
points_df = pd.DataFrame(columns=['Latitude', 'Longitude', 'Height'])
for i, row in df.iterrows():
x1, y1, z1 = earthConverter(row['Latitude'], row['Longitude'], row['Height'])
temp_df = pd.DataFrame({'Latitude': x1,
'Longitude': y1,
'Height': z1}, index=[0])
points_df = points_df.append(temp_df, ignore_index=True)
points_df.to_csv(output_file)
new_csv('worksheet.csv', 'new_worksheet.csv')