How Can I Create Variables From Text and Convert Coordinates-CodePudding

I am aware there are similar questions to mine, but after trying numerous "answers" over several hours I thought my best next step is submit my conundrum here. I respect your time.

After several hours with no success in understanding why my Python script won't work I decided to see if someone could help me. Essentially, the goal is to use the astronomical program, "Stellarium" as a "day and night sky" to practice Celestial Navigation (CelNav) navigating the simulated world of Microsoft Flight Simulator X (FSX). The script actually writes a "startup.ssc" script which initializes Stellarium's date, time, and position.

The process is thus...

Use FSX and save a "flight." This creates a *.FLT file which is a text file which saves the complete situation, including time and location.
Run the FSXtoStellarium.py
Locate the lines of date, time, latitude, longitude, and altitude in the *.FLT text.
Read the data into variables.
Convert the Degrees(°), Minutes('), Seconds(") (DMS) to Decimal Degrees (DD).
Lastly, the script constructs a "startup.ssc" and opens Stellarium at the recorded time and place.

The Problem: I have not been able to read the DMS into variable(s) correctly nor can I format the DMS into Decimal Degrees (DD). According to the "watches" I set in my IDE (PyScripter), the script is reading in an "int" value I can't decipher instead of the text string of the DMS (Example: W157° 27' 23.20").

Here are some excerpts of the file and script.

HMS Bounty.FLT

Various lines of data above...

[SimVars.0]
Latitude=N21° 20' 47.36"
Longitude=W157° 27' 23.20"
Altitude= 000004.93

Various lines of data below...
EOF

FSXtoStellarium.py

Various lines of script above...

# find lat & Lon in the file
start = content.find("SimVars.0")
latstart = content.find("Latitude=")
latend = content.find("Latitude=",latstart 1)
longstart = content.find("Longitude=",start)
longend = content.find(",",longstart)

# convert to dec deg
latitude = float(content[longend 1:latend])/120000
longitude = float(content[longstart 10:longend])/120000

Various lines of script below...

So, what am I missing?

FYI - I am an old man who gets confused. My professional career was in COBOL/DB2/CICS, but you can consider me a Python newbie (it shows, right?). :)

Your help s greatly appreciated and I will gladly provide any additional information.

Calvin

CodePudding user response：

Here is a way to get from the text file (with multiple input lines) all the way to Decimal Degrees in python 2.7:

from __future__ import print_function
content='''
[SimVars.0]
Latitude=N21° 20' 47.36"
Longitude=W157° 27' 23.20"
'''

latKey = "Latitude="
longKey = "Longitude="

latstart = content.index(latKey)   len(latKey)
latend = content.find('"', latstart)   1
longstart = content.find(longKey, latend)   len(longKey)
longend = content.find('"', longstart)   1

lat = content[latstart:latend]
long = content[longstart:longend]

print()
print('lat ', lat)
print('long ', long)

deg, mnt, sec = [float(x[:-1]) for x in lat[1:].split()]
latVal = deg   mnt / 60   sec / 3600

deg, mnt, sec = [float(x[:-1]) for x in long[1:].split()]
longVal = deg   mnt / 60   sec / 3600

print()
print('latVal ', latVal)
print('longVal ', longVal)

Explanation:

we start with a multi-line string, content
the first index() call finds the start position of the substring "Latitude=" within content, to which we add the length of "Latitude=" since what we care about is the characters following the = character
the second index() call searches for the 'seconds' character " (which marks the end of the Latitude substring), to which we add one (for the length of the ")
the third index() call does for Longitude= something similar to what we did for latitude, except it starts at the position latend since we expect Longitude= to follow the latitude string following Latitude=
the fourth index() call seeks the end of the longitude substring and is completely analogous to the second index() call above for latitude
the assignment to lat uses square bracket slice notation for the list content to extract the substring from the end of Latitude= to the subsequent " character
the assignment to long is analogous to the previous step
the first assignment to deg, mnt, sec is assigning a tuple of 3 values to these variables using a list comprehension:
- split lat[1:], which is to say lat with the leading cardinal direction character N removed, into space-delimited tokens 21°, 20' and 47.36"
- for each token, x[:-1] uses slice notation to drop the final character which gives strings 21, 20 and 47.36
- float() converts these strings to numbers of type float
the assignment to latVal does the necessary arithmetic to calculate a quantity in decimal degrees using the degrees, minutes and seconds stored in deg, mnt, sec.
the treatment of long to get to longVal is completely analogous to that for lat and latVal above.

Output:

lat  N21° 20' 47.36"
long  W157° 27' 23.20"

latVal  21.34648888888889
longVal  157.45644444444443