#--------------------- Program LatLongGrid Documentation -------------------
# LatLongGrid.py: program to construct a grid of latitude-longitude points in
# a text file. The text file can be imported into ArcGIS 10.1 as decimal
# lat-long points (geographic) that can be used to georeference scanned
# raster images that contain lat-long reference points. Input for the program
# is taken from the command line:
# 1st parameter: output file name
# 2nd parameter: lower left (SW) corner longitude {+/-}DDDMMSS format
# 3rd parameter: lower left (SW) corner latitude {+/-}DDMMSS format
# 4th parameter: upper right (NE) corner longitude {+/-}DDDMMSS format
# 5th parameter: upper right (NE) corner latitude {+/-}DDMMSS format
# 6th parameter: longitude spacing for grid in DDDMMSS format
# 7th parameter: latitude spacing for grid in DDMMSS format
# The output text file will be a comma delimited 3 column format:
# 1st column: longitude coordinate in decimal degree format.
# 2nd column: latitude coordinate in decimal degree format.
# 3rd column: grid point number starting with 1 at SW corner and incremented
# by row and then column. Last (highest) point number is the NE corner.
#
#--------------------------------------------------------------------------
import arcpy
import sys
#----------------------- Function Definitions -----------------------------
def LongStr2DD(longstr):
    long_dd = 0.0
    sfact = 1.0
    if longstr[0] == "-" :
        sfact = -1.0
    long_dd = float(longstr[1:4])+float(longstr[4:6])/60.0+float(longstr[6:8])/3600.0
    long_dd = long_dd * sfact
    return long_dd

def LatStr2DD(latstr):
 #  Insert your code here!
    return lat_dd

def CheckLongStr (longstr):
    if len(longstr) == 7:
       longstr = "+"+longstr
    return longstr

def CheckLatStr(latstr):
#  Insert your code here!
    return latstr

#------------------------ Main Program Code -------------------------------
# Initialize constants
longstrlen = 8
latstrlen = 7
ofn="grid.txt"
dl = ","
eoln = "\n"
err_msg = "unknown error"

# get input from parameter string. Test program with below examples:
# ex.  c:/temp/grid.txt -0860000 +325230 -0855230 +330000 000230 000230 (Alex City AL 1:24,000)
# ex.  c:/temp/grid.txt -0870000 +320000 -0860000 +323000 000730 000730 (Montgomery AL 1:100,000)
# ex.  c:/temp/grid.txt -0880000 +320000 -0860000 +330000 001500 001500 (Montgomery AL 1:250,000) 

try: 
    ofn = sys.argv[1] 
    SW_longstr = CheckLongStr(sys.argv[2])
    SW_latstr = CheckLatStr(sys.argv[3])
    NE_longstr = CheckLongStr(sys.argv[4])
    NE_latstr = CheckLatStr(sys.argv[5])
    long_spcstr = sys.argv[6]
    lat_spcstr = sys.argv[7]
        
# check parameter strings for proper length
    if len(SW_longstr) <> longstrlen :
        err_msg = "ERROR: SW corner longitude parameter incorrect format"
        raise exception
    
    if len(SW_latstr) <> latstrlen :
        err_msg = "ERROR: SW corner latitude parameter incorrect format"
        raise exception

    if len(NE_longstr) <> longstrlen :
        err_msg = "ERROR: NE corner longitude parameter incorrect format" 
        raise exception

    if len(NE_latstr) <> latstrlen :
        err_msg = "ERROR: NE corner latitude parameter incorrect format"
        raise exception

    if len(long_spcstr) <> 6 :
        err_msg = "ERROR: longitude spacing parameter incorrect format"
        raise exception

    if len(lat_spcstr) <> 6 :
        err_msg = "ERROR: latitude spacing parameter incorrect format"
        raise exception

# open text file for write output
    of = open(ofn,"w")
    of.write("Longitude"+dl+"Latitude"+dl+"No."+eoln)
    sw_long_dd = LongStr2DD(SW_longstr)
    sw_lat_dd = LatStr2DD(SW_latstr)
    ne_long_dd = LongStr2DD(NE_longstr)
    ne_lat_dd = LatStr2DD(NE_latstr)
    longspc_dd = LongStr2DD("+0"+long_spcstr)
    latspc_dd = LatStr2DD("+"+lat_spcstr)
    nrows =  # insert your expression here!
    ncols =  # insert your expression here!
    count = 0
    i = 0
    while i < nrows:
        lat_dd = sw_lat_dd + i * latspc_dd
        i = i + 1
        j = 0
        while j < ncols:
            long_dd = sw_long_dd + j * longspc_dd
            j = j + 1
            count = count + 1
            of.write(str(long_dd)+dl+str(lat_dd)+dl+str(count)+eoln)
            
    print ofn+" has been sucessfully created."+eoln        

except (IndexError):
    err_msg = "No command line parameters or missing command line parameter!"
    print err_msg
    print "command line syntax: {output file} {SW long} {SW lat} {NE long} {NE lat} {long spacing} {lat spacing}"
    print "example command line: c:/temp/grid.txt -0860000 +325230 -0855230 +330000 000230 000230"
except:
    print err_msg
    print "example command line: c:/temp/grid.txt -0860000 +325230 -0855230 +330000 000230 000230"    
finally:
# close the output file
    if not(of.closed) :
        of.close()


#----------- Program End ------------------------------------------------