yodaUtility/sgp4/cTle.cpp

//
// cTle.cpp
// This class encapsulates a single set of standard NORAD two line elements.
//
// Copyright 1996-2005 Michael F. Henry
//
#include "stdafx.h"

#include "cTle.h"

// Note: The column offsets are ZERO based.

// Name
const int TLE_LEN_LINE_DATA      = 69; const int TLE_LEN_LINE_NAME      = 22;

// Line 1
const int TLE1_COL_SATNUM        =  2; const int TLE1_LEN_SATNUM        =  5;
const int TLE1_COL_INTLDESC_A    =  9; const int TLE1_LEN_INTLDESC_A    =  2;
const int TLE1_COL_INTLDESC_B    = 11; const int TLE1_LEN_INTLDESC_B    =  3;
const int TLE1_COL_INTLDESC_C    = 14; const int TLE1_LEN_INTLDESC_C    =  3;
const int TLE1_COL_EPOCH_A       = 18; const int TLE1_LEN_EPOCH_A       =  2;
const int TLE1_COL_EPOCH_B       = 20; const int TLE1_LEN_EPOCH_B       = 12;
const int TLE1_COL_MEANMOTIONDT  = 33; const int TLE1_LEN_MEANMOTIONDT  = 10;
const int TLE1_COL_MEANMOTIONDT2 = 44; const int TLE1_LEN_MEANMOTIONDT2 =  8;
const int TLE1_COL_BSTAR         = 53; const int TLE1_LEN_BSTAR         =  8;
const int TLE1_COL_EPHEMTYPE     = 62; const int TLE1_LEN_EPHEMTYPE     =  1;
const int TLE1_COL_ELNUM         = 64; const int TLE1_LEN_ELNUM         =  4;

// Line 2
const int TLE2_COL_SATNUM        = 2;  const int TLE2_LEN_SATNUM        =  5;
const int TLE2_COL_INCLINATION   = 8;  const int TLE2_LEN_INCLINATION   =  8;
const int TLE2_COL_RAASCENDNODE  = 17; const int TLE2_LEN_RAASCENDNODE  =  8;
const int TLE2_COL_ECCENTRICITY  = 26; const int TLE2_LEN_ECCENTRICITY  =  7;
const int TLE2_COL_ARGPERIGEE    = 34; const int TLE2_LEN_ARGPERIGEE    =  8;
const int TLE2_COL_MEANANOMALY   = 43; const int TLE2_LEN_MEANANOMALY   =  8;
const int TLE2_COL_MEANMOTION    = 52; const int TLE2_LEN_MEANMOTION    = 11;
const int TLE2_COL_REVATEPOCH    = 63; const int TLE2_LEN_REVATEPOCH    =  5;

/////////////////////////////////////////////////////////////////////////////
cTle::cTle(string& strName, string& strLine1, string& strLine2)
{
   m_strName  = strName;
   m_strLine1 = strLine1;
   m_strLine2 = strLine2;

   Initialize();
}

/////////////////////////////////////////////////////////////////////////////
cTle::cTle(const cTle &tle)
{
   m_strName  = tle.m_strName;
   m_strLine1 = tle.m_strLine1;
   m_strLine2 = tle.m_strLine2;

   for (int fld = FLD_FIRST; fld < FLD_LAST; fld++)
   {
      m_Field[fld] = tle.m_Field[fld];
   }

   m_mapCache = tle.m_mapCache;
}

/////////////////////////////////////////////////////////////////////////////
cTle::~cTle()
{
}

/////////////////////////////////////////////////////////////////////////////
// getField()
// Return requested field as a double (function return value) or as a text
// string (*pstr) in the units requested (eUnit). Set 'bStrUnits' to true 
// to have units appended to text string.
//
// Note: numeric return values are cached; asking for the same field more
// than once incurs minimal overhead.
double cTle::getField(eField   fld, 
                      eUnits   units,    /* = U_NATIVE */
                      string  *pstr      /* = NULL     */,
                      bool     bStrUnits /* = false    */) const
{
   assert((FLD_FIRST <= fld) && (fld < FLD_LAST));
   assert((U_FIRST <= units) && (units < U_LAST));

   if (pstr)
   {
      // Return requested field in string form.
      *pstr = m_Field[fld];
      
      if (bStrUnits)
         *pstr += getUnits(fld);
      
      return 0.0;
   }
   else
   {
      // Return requested field in floating-point form.
      // Return cache contents if it exists, else populate cache
      FldKey key = Key(units, fld);

      if (m_mapCache.find(key) == m_mapCache.end())
      {
         // Value not in cache; add it
         double valNative = atof(m_Field[fld].c_str());
         double valConv   = ConvertUnits(valNative, fld, units); 
         m_mapCache[key]  = valConv;

         return valConv;
      }
      else
      {
         // return cached value
         return m_mapCache[key];
      }
   }
}

//////////////////////////////////////////////////////////////////////////////
// Convert the given field into the requested units. It is assumed that
// the value being converted is in the TLE format's "native" form.
double cTle::ConvertUnits(double valNative, // value to convert
                          eField fld,       // what field the value is
                          eUnits units)     // what units to convert to
{
   switch (fld)
   {
      case FLD_I:
      case FLD_RAAN:
      case FLD_ARGPER:
      case FLD_M:
      {
         // The native TLE format is DEGREES
         if (units == U_RAD)
            return valNative * RADS_PER_DEG;
      }
   }

   return valNative; // return value in unconverted native format
}

//////////////////////////////////////////////////////////////////////////////
string cTle::getUnits(eField fld) const 
{
   static const string strDegrees    = " degrees";
   static const string strRevsPerDay = " revs / day";
   static const string strNull;

   switch (fld)
   {
      case FLD_I:
      case FLD_RAAN:
      case FLD_ARGPER:
      case FLD_M:
         return strDegrees;

      case FLD_MMOTION:
         return strRevsPerDay;

      default:
         return strNull;   
   }
}

/////////////////////////////////////////////////////////////////////////////
// ExpToDecimal()
// Converts TLE-style exponential notation of the form [ |-]00000[+|-]0 to
// decimal notation. Assumes implied decimal point to the left of the first
// number in the string, i.e., 
//       " 12345-3" =  0.00012345
//       "-23429-5" = -0.0000023429   
//       " 40436+1" =  4.0436
string cTle::ExpToDecimal(const string &str)
{
   const int COL_EXP_SIGN = 6;
   const int LEN_EXP      = 2;
   
   const int LEN_BUFREAL  = 32;   // max length of buffer to hold floating point
                                 // representation of input string.
   int nMan;
   int nExp;      
   
   // sscanf(%d) will read up to the exponent sign
   sscanf(str.c_str(), "%d", &nMan);
   
   double dblMan = nMan;
   bool  bNeg    = (nMan < 0);
   
   if (bNeg)
      dblMan *= -1;
   
   // Move decimal place to left of first digit
   while (dblMan >= 1.0)
      dblMan /= 10.0;
   
   if (bNeg)
      dblMan *= -1;
   
   // now read exponent
   sscanf(str.substr(COL_EXP_SIGN, LEN_EXP).c_str(), "%d", &nExp);
   
   double dblVal = dblMan * pow(10.0, nExp);
   char szVal[LEN_BUFREAL];
   
   snprintf(szVal, sizeof(szVal), "%.9f", dblVal);
   
   string strVal = szVal;
   
   return strVal;
   
} // ExpToDecimal()

/////////////////////////////////////////////////////////////////////////////
// Initialize()
// Initialize the string array.
void cTle::Initialize()
{
   // Have we already been initialized?
   if (m_Field[FLD_NORADNUM].size())
      return;
   
   assert(!m_strName.empty());
   assert(!m_strLine1.empty());
   assert(!m_strLine2.empty());
   
   m_Field[FLD_NORADNUM] = m_strLine1.substr(TLE1_COL_SATNUM, TLE1_LEN_SATNUM);
   m_Field[FLD_INTLDESC] = m_strLine1.substr(TLE1_COL_INTLDESC_A,
                                             TLE1_LEN_INTLDESC_A +
                                             TLE1_LEN_INTLDESC_B +   
                                             TLE1_LEN_INTLDESC_C);   
   m_Field[FLD_EPOCHYEAR] = 
         m_strLine1.substr(TLE1_COL_EPOCH_A, TLE1_LEN_EPOCH_A);

   m_Field[FLD_EPOCHDAY] = 
         m_strLine1.substr(TLE1_COL_EPOCH_B, TLE1_LEN_EPOCH_B);
   
   if (m_strLine1[TLE1_COL_MEANMOTIONDT] == '-')
   {
      // value is negative
      m_Field[FLD_MMOTIONDT] = "-0";
   }
   else
      m_Field[FLD_MMOTIONDT] = "0";
   
   m_Field[FLD_MMOTIONDT] += m_strLine1.substr(TLE1_COL_MEANMOTIONDT + 1,
                                               TLE1_LEN_MEANMOTIONDT);
   
   // decimal point assumed; exponential notation
   m_Field[FLD_MMOTIONDT2] = ExpToDecimal(
                                 m_strLine1.substr(TLE1_COL_MEANMOTIONDT2,
                                                   TLE1_LEN_MEANMOTIONDT2));
   // decimal point assumed; exponential notation
   m_Field[FLD_BSTAR] = ExpToDecimal(m_strLine1.substr(TLE1_COL_BSTAR,
                                                       TLE1_LEN_BSTAR));
   //TLE1_COL_EPHEMTYPE      
   //TLE1_LEN_EPHEMTYPE   
   m_Field[FLD_SET] = m_strLine1.substr(TLE1_COL_ELNUM, TLE1_LEN_ELNUM);
   
   TrimLeft(m_Field[FLD_SET]);
   
   //TLE2_COL_SATNUM         
   //TLE2_LEN_SATNUM         
   
   m_Field[FLD_I] = m_strLine2.substr(TLE2_COL_INCLINATION,
                                      TLE2_LEN_INCLINATION);
   TrimLeft(m_Field[FLD_I]);
   
   m_Field[FLD_RAAN] = m_strLine2.substr(TLE2_COL_RAASCENDNODE,
                                         TLE2_LEN_RAASCENDNODE);
   TrimLeft(m_Field[FLD_RAAN]);

   // decimal point is assumed
   m_Field[FLD_E]   = "0.";
   m_Field[FLD_E]   += m_strLine2.substr(TLE2_COL_ECCENTRICITY,
                                       TLE2_LEN_ECCENTRICITY);
   
   m_Field[FLD_ARGPER] = m_strLine2.substr(TLE2_COL_ARGPERIGEE,
                                           TLE2_LEN_ARGPERIGEE);
   TrimLeft(m_Field[FLD_ARGPER]);
   
   m_Field[FLD_M]   = m_strLine2.substr(TLE2_COL_MEANANOMALY,
                                      TLE2_LEN_MEANANOMALY);
   TrimLeft(m_Field[FLD_M]);
   
   m_Field[FLD_MMOTION]   = m_strLine2.substr(TLE2_COL_MEANMOTION, 
                                            TLE2_LEN_MEANMOTION);
   TrimLeft(m_Field[FLD_MMOTION]);
   
   m_Field[FLD_ORBITNUM] = m_strLine2.substr(TLE2_COL_REVATEPOCH,
                                             TLE2_LEN_REVATEPOCH);
   TrimLeft(m_Field[FLD_ORBITNUM]);
   
} // InitStrVars()

/////////////////////////////////////////////////////////////////////////////
// IsTleFormat()
// Returns true if "str" is a valid data line of a two-line element set,
//   else false.
//
// To be valid a line must:
//      Have as the first character the line number
//      Have as the second character a blank
//      Be TLE_LEN_LINE_DATA characters long
//      Have a valid checksum (note: no longer required as of 12/96)
//      
bool cTle::IsValidLine(string& str, eTleLine line)
{
   TrimLeft(str);
   TrimRight(str);
   
   size_t nLen = str.size();
   
   if (nLen != TLE_LEN_LINE_DATA)
      return false;
   
   // First char in string must be line number
   if ((str[0] - '0') != line)
      return false;
   
   // Second char in string must be blank
   if (str[1] != ' ')
      return false;
   
   /*
      NOTE: 12/96 
      The requirement that the last char in the line data must be a valid 
      checksum is too restrictive. 
      
      // Last char in string must be checksum
      int nSum = CheckSum(str);
     
      if (nSum != (str[TLE_LEN_LINE_DATA - 1] - '0'))
         return false;
   */
   
   return true;
   
} // IsTleFormat()

/////////////////////////////////////////////////////////////////////////////
// CheckSum()
// Calculate the check sum for a given line of TLE data, the last character
// of which is the current checksum. (Although there is no check here,
// the current checksum should match the one we calculate.)
// The checksum algorithm: 
//      Each number in the data line is summed, modulo 10.
//    Non-numeric characters are zero, except minus signs, which are 1.
//
int cTle::CheckSum(const string& str)
{
   // The length is "- 1" because we don't include the current (existing)
   // checksum character in the checksum calculation.
   size_t len = str.size() - 1;
   int xsum = 0;
   
   for (size_t i = 0; i < len; i++)
   {
      char ch = str[i];
      if (isdigit(ch))
         xsum += (ch - '0');
      else if (ch == '-')
         xsum++;
   }
   
   return (xsum % 10);
   
} // CheckSum()

/////////////////////////////////////////////////////////////////////////////
void cTle::TrimLeft(string& s)
{
   while (s[0] == ' ')
      s.erase(0, 1);
}

/////////////////////////////////////////////////////////////////////////////
void cTle::TrimRight(string& s)
{
   while (s[s.size() - 1] == ' ')
      s.erase(s.size() - 1);
}

1	//
2	// cTle.cpp
3	// This class encapsulates a single set of standard NORAD two line elements.
4	//
5	// Copyright 1996-2005 Michael F. Henry
6	//
7	#include "stdafx.h"
8
9	#include "cTle.h"
10
11	// Note: The column offsets are ZERO based.
12
13	// Name
14	const int TLE_LEN_LINE_DATA = 69; const int TLE_LEN_LINE_NAME = 22;
15
16	// Line 1
17	const int TLE1_COL_SATNUM = 2; const int TLE1_LEN_SATNUM = 5;
18	const int TLE1_COL_INTLDESC_A = 9; const int TLE1_LEN_INTLDESC_A = 2;
19	const int TLE1_COL_INTLDESC_B = 11; const int TLE1_LEN_INTLDESC_B = 3;
20	const int TLE1_COL_INTLDESC_C = 14; const int TLE1_LEN_INTLDESC_C = 3;
21	const int TLE1_COL_EPOCH_A = 18; const int TLE1_LEN_EPOCH_A = 2;
22	const int TLE1_COL_EPOCH_B = 20; const int TLE1_LEN_EPOCH_B = 12;
23	const int TLE1_COL_MEANMOTIONDT = 33; const int TLE1_LEN_MEANMOTIONDT = 10;
24	const int TLE1_COL_MEANMOTIONDT2 = 44; const int TLE1_LEN_MEANMOTIONDT2 = 8;
25	const int TLE1_COL_BSTAR = 53; const int TLE1_LEN_BSTAR = 8;
26	const int TLE1_COL_EPHEMTYPE = 62; const int TLE1_LEN_EPHEMTYPE = 1;
27	const int TLE1_COL_ELNUM = 64; const int TLE1_LEN_ELNUM = 4;
28
29	// Line 2
30	const int TLE2_COL_SATNUM = 2; const int TLE2_LEN_SATNUM = 5;
31	const int TLE2_COL_INCLINATION = 8; const int TLE2_LEN_INCLINATION = 8;
32	const int TLE2_COL_RAASCENDNODE = 17; const int TLE2_LEN_RAASCENDNODE = 8;
33	const int TLE2_COL_ECCENTRICITY = 26; const int TLE2_LEN_ECCENTRICITY = 7;
34	const int TLE2_COL_ARGPERIGEE = 34; const int TLE2_LEN_ARGPERIGEE = 8;
35	const int TLE2_COL_MEANANOMALY = 43; const int TLE2_LEN_MEANANOMALY = 8;
36	const int TLE2_COL_MEANMOTION = 52; const int TLE2_LEN_MEANMOTION = 11;
37	const int TLE2_COL_REVATEPOCH = 63; const int TLE2_LEN_REVATEPOCH = 5;
38
39	/////////////////////////////////////////////////////////////////////////////
40	cTle::cTle(string& strName, string& strLine1, string& strLine2)
41	{
42	m_strName = strName;
43	m_strLine1 = strLine1;
44	m_strLine2 = strLine2;
45
46	Initialize();
47	}
48
49	/////////////////////////////////////////////////////////////////////////////
50	cTle::cTle(const cTle &tle)
51	{
52	m_strName = tle.m_strName;
53	m_strLine1 = tle.m_strLine1;
54	m_strLine2 = tle.m_strLine2;
55
56	for (int fld = FLD_FIRST; fld < FLD_LAST; fld++)
57	{
58	m_Field[fld] = tle.m_Field[fld];
59	}
60
61	m_mapCache = tle.m_mapCache;
62	}
63
64	/////////////////////////////////////////////////////////////////////////////
65	cTle::~cTle()
66	{
67	}
68
69	/////////////////////////////////////////////////////////////////////////////
70	// getField()
71	// Return requested field as a double (function return value) or as a text
72	// string (*pstr) in the units requested (eUnit). Set 'bStrUnits' to true
73	// to have units appended to text string.
74	//
75	// Note: numeric return values are cached; asking for the same field more
76	// than once incurs minimal overhead.
77	double cTle::getField(eField fld,
78	eUnits units, /* = U_NATIVE */
79	string pstr / = NULL */,
80	bool bStrUnits /* = false */) const
81	{
82	assert((FLD_FIRST <= fld) && (fld < FLD_LAST));
83	assert((U_FIRST <= units) && (units < U_LAST));
84
85	if (pstr)
86	{
87	// Return requested field in string form.
88	*pstr = m_Field[fld];
89
90	if (bStrUnits)
91	*pstr += getUnits(fld);
92
93	return 0.0;
94	}
95	else
96	{
97	// Return requested field in floating-point form.
98	// Return cache contents if it exists, else populate cache
99	FldKey key = Key(units, fld);
100
101	if (m_mapCache.find(key) == m_mapCache.end())
102	{
103	// Value not in cache; add it
104	double valNative = atof(m_Field[fld].c_str());
105	double valConv = ConvertUnits(valNative, fld, units);
106	m_mapCache[key] = valConv;
107
108	return valConv;
109	}
110	else
111	{
112	// return cached value
113	return m_mapCache[key];
114	}
115	}
116	}
117
118	//////////////////////////////////////////////////////////////////////////////
119	// Convert the given field into the requested units. It is assumed that
120	// the value being converted is in the TLE format's "native" form.
121	double cTle::ConvertUnits(double valNative, // value to convert
122	eField fld, // what field the value is
123	eUnits units) // what units to convert to
124	{
125	switch (fld)
126	{
127	case FLD_I:
128	case FLD_RAAN:
129	case FLD_ARGPER:
130	case FLD_M:
131	{
132	// The native TLE format is DEGREES
133	if (units == U_RAD)
134	return valNative * RADS_PER_DEG;
135	}
136	}
137
138	return valNative; // return value in unconverted native format
139	}
140
141	//////////////////////////////////////////////////////////////////////////////
142	string cTle::getUnits(eField fld) const
143	{
144	static const string strDegrees = " degrees";
145	static const string strRevsPerDay = " revs / day";
146	static const string strNull;
147
148	switch (fld)
149	{
150	case FLD_I:
151	case FLD_RAAN:
152	case FLD_ARGPER:
153	case FLD_M:
154	return strDegrees;
155
156	case FLD_MMOTION:
157	return strRevsPerDay;
158
159	default:
160	return strNull;
161	}
162	}
163
164	/////////////////////////////////////////////////////////////////////////////
165	// ExpToDecimal()
166	// Converts TLE-style exponential notation of the form [ \|-]00000[+\|-]0 to
167	// decimal notation. Assumes implied decimal point to the left of the first
168	// number in the string, i.e.,
169	// " 12345-3" = 0.00012345
170	// "-23429-5" = -0.0000023429
171	// " 40436+1" = 4.0436
172	string cTle::ExpToDecimal(const string &str)
173	{
174	const int COL_EXP_SIGN = 6;
175	const int LEN_EXP = 2;
176
177	const int LEN_BUFREAL = 32; // max length of buffer to hold floating point
178	// representation of input string.
179	int nMan;
180	int nExp;
181
182	// sscanf(%d) will read up to the exponent sign
183	sscanf(str.c_str(), "%d", &nMan);
184
185	double dblMan = nMan;
186	bool bNeg = (nMan < 0);
187
188	if (bNeg)
189	dblMan *= -1;
190
191	// Move decimal place to left of first digit
192	while (dblMan >= 1.0)
193	dblMan /= 10.0;
194
195	if (bNeg)
196	dblMan *= -1;
197
198	// now read exponent
199	sscanf(str.substr(COL_EXP_SIGN, LEN_EXP).c_str(), "%d", &nExp);
200
201	double dblVal = dblMan * pow(10.0, nExp);
202	char szVal[LEN_BUFREAL];
203
204	snprintf(szVal, sizeof(szVal), "%.9f", dblVal);
205
206	string strVal = szVal;
207
208	return strVal;
209
210	} // ExpToDecimal()
211
212	/////////////////////////////////////////////////////////////////////////////
213	// Initialize()
214	// Initialize the string array.
215	void cTle::Initialize()
216	{
217	// Have we already been initialized?
218	if (m_Field[FLD_NORADNUM].size())
219	return;
220
221	assert(!m_strName.empty());
222	assert(!m_strLine1.empty());
223	assert(!m_strLine2.empty());
224
225	m_Field[FLD_NORADNUM] = m_strLine1.substr(TLE1_COL_SATNUM, TLE1_LEN_SATNUM);
226	m_Field[FLD_INTLDESC] = m_strLine1.substr(TLE1_COL_INTLDESC_A,
227	TLE1_LEN_INTLDESC_A +
228	TLE1_LEN_INTLDESC_B +
229	TLE1_LEN_INTLDESC_C);
230	m_Field[FLD_EPOCHYEAR] =
231	m_strLine1.substr(TLE1_COL_EPOCH_A, TLE1_LEN_EPOCH_A);
232
233	m_Field[FLD_EPOCHDAY] =
234	m_strLine1.substr(TLE1_COL_EPOCH_B, TLE1_LEN_EPOCH_B);
235
236	if (m_strLine1[TLE1_COL_MEANMOTIONDT] == '-')
237	{
238	// value is negative
239	m_Field[FLD_MMOTIONDT] = "-0";
240	}
241	else
242	m_Field[FLD_MMOTIONDT] = "0";
243
244	m_Field[FLD_MMOTIONDT] += m_strLine1.substr(TLE1_COL_MEANMOTIONDT + 1,
245	TLE1_LEN_MEANMOTIONDT);
246
247	// decimal point assumed; exponential notation
248	m_Field[FLD_MMOTIONDT2] = ExpToDecimal(
249	m_strLine1.substr(TLE1_COL_MEANMOTIONDT2,
250	TLE1_LEN_MEANMOTIONDT2));
251	// decimal point assumed; exponential notation
252	m_Field[FLD_BSTAR] = ExpToDecimal(m_strLine1.substr(TLE1_COL_BSTAR,
253	TLE1_LEN_BSTAR));
254	//TLE1_COL_EPHEMTYPE
255	//TLE1_LEN_EPHEMTYPE
256	m_Field[FLD_SET] = m_strLine1.substr(TLE1_COL_ELNUM, TLE1_LEN_ELNUM);
257
258	TrimLeft(m_Field[FLD_SET]);
259
260	//TLE2_COL_SATNUM
261	//TLE2_LEN_SATNUM
262
263	m_Field[FLD_I] = m_strLine2.substr(TLE2_COL_INCLINATION,
264	TLE2_LEN_INCLINATION);
265	TrimLeft(m_Field[FLD_I]);
266
267	m_Field[FLD_RAAN] = m_strLine2.substr(TLE2_COL_RAASCENDNODE,
268	TLE2_LEN_RAASCENDNODE);
269	TrimLeft(m_Field[FLD_RAAN]);
270
271	// decimal point is assumed
272	m_Field[FLD_E] = "0.";
273	m_Field[FLD_E] += m_strLine2.substr(TLE2_COL_ECCENTRICITY,
274	TLE2_LEN_ECCENTRICITY);
275
276	m_Field[FLD_ARGPER] = m_strLine2.substr(TLE2_COL_ARGPERIGEE,
277	TLE2_LEN_ARGPERIGEE);
278	TrimLeft(m_Field[FLD_ARGPER]);
279
280	m_Field[FLD_M] = m_strLine2.substr(TLE2_COL_MEANANOMALY,
281	TLE2_LEN_MEANANOMALY);
282	TrimLeft(m_Field[FLD_M]);
283
284	m_Field[FLD_MMOTION] = m_strLine2.substr(TLE2_COL_MEANMOTION,
285	TLE2_LEN_MEANMOTION);
286	TrimLeft(m_Field[FLD_MMOTION]);
287
288	m_Field[FLD_ORBITNUM] = m_strLine2.substr(TLE2_COL_REVATEPOCH,
289	TLE2_LEN_REVATEPOCH);
290	TrimLeft(m_Field[FLD_ORBITNUM]);
291
292	} // InitStrVars()
293
294	/////////////////////////////////////////////////////////////////////////////
295	// IsTleFormat()
296	// Returns true if "str" is a valid data line of a two-line element set,
297	// else false.
298	//
299	// To be valid a line must:
300	// Have as the first character the line number
301	// Have as the second character a blank
302	// Be TLE_LEN_LINE_DATA characters long
303	// Have a valid checksum (note: no longer required as of 12/96)
304	//
305	bool cTle::IsValidLine(string& str, eTleLine line)
306	{
307	TrimLeft(str);
308	TrimRight(str);
309
310	size_t nLen = str.size();
311
312	if (nLen != TLE_LEN_LINE_DATA)
313	return false;
314
315	// First char in string must be line number
316	if ((str[0] - '0') != line)
317	return false;
318
319	// Second char in string must be blank
320	if (str[1] != ' ')
321	return false;
322
323	/*
324	NOTE: 12/96
325	The requirement that the last char in the line data must be a valid
326	checksum is too restrictive.
327
328	// Last char in string must be checksum
329	int nSum = CheckSum(str);
330
331	if (nSum != (str[TLE_LEN_LINE_DATA - 1] - '0'))
332	return false;
333	*/
334
335	return true;
336
337	} // IsTleFormat()
338
339	/////////////////////////////////////////////////////////////////////////////
340	// CheckSum()
341	// Calculate the check sum for a given line of TLE data, the last character
342	// of which is the current checksum. (Although there is no check here,
343	// the current checksum should match the one we calculate.)
344	// The checksum algorithm:
345	// Each number in the data line is summed, modulo 10.
346	// Non-numeric characters are zero, except minus signs, which are 1.
347	//
348	int cTle::CheckSum(const string& str)
349	{
350	// The length is "- 1" because we don't include the current (existing)
351	// checksum character in the checksum calculation.
352	size_t len = str.size() - 1;
353	int xsum = 0;
354
355	for (size_t i = 0; i < len; i++)
356	{
357	char ch = str[i];
358	if (isdigit(ch))
359	xsum += (ch - '0');
360	else if (ch == '-')
361	xsum++;
362	}
363
364	return (xsum % 10);
365
366	} // CheckSum()
367
368	/////////////////////////////////////////////////////////////////////////////
369	void cTle::TrimLeft(string& s)
370	{
371	while (s[0] == ' ')
372	s.erase(0, 1);
373	}
374
375	/////////////////////////////////////////////////////////////////////////////
376	void cTle::TrimRight(string& s)
377	{
378	while (s[s.size() - 1] == ' ')
379	s.erase(s.size() - 1);
380	}
381