diff options
| -rw-r--r-- | core/divelist.c | 41 |
1 files changed, 5 insertions, 36 deletions
diff --git a/core/divelist.c b/core/divelist.c index 02e5cfc4a..3c8d306ea 100644 --- a/core/divelist.c +++ b/core/divelist.c @@ -161,35 +161,6 @@ static int calculate_otu(const struct dive *dive) return lrint(otu); } -/* Table of maximum oxygen exposure durations, used in CNS calulations. - This table shows the official NOAA maximum O2 exposure limits (in seconds) for different PO2 values. It also gives - slope values for linear interpolation for intermediate PO2 values between the tabulated PO2 values in the 1st column. - Top & bottom rows are inserted that are not in the NOAA table: (1) For PO2 > 1.6 the same slope value as between - 1.5 & 1.6 is used. This exptrapolation for PO2 > 1.6 likely gives an underestimate above 1.6 but is better than the - value for PO2=1.6 (45 min). (2) The NOAA table only tabulates values for PO2 >= 0.6. Since O2-uptake occurs down to - PO2=0.5, the same slope is used as for 0.7 > PO2 > 0.6. This gives a conservative estimate for 0.6 > PO2 > 0.5. To - preserve the integer structure of the table, all slopes are given as slope*10: divide by 10 to get the valid slope. - The columns below are: - po2 (mbar), Maximum Single Exposure (seconds), single_slope, Maximum 24 hour Exposure (seconds), 24h_slope */ -enum cns_table_headers {PO2VAL, SINGLE_EXP, SINGLE_SLOPE, DAILY_EXP, DAILY_SLOPE, NO_COLUMNS}; -static int const cns_table[][5] = { - { 1600, 45 * 60, 456, 150 * 60, 180 }, - { 1550, 83 * 60, 456, 165 * 60, 180 }, - { 1500, 120 * 60, 444, 180 * 60, 180 }, - { 1450, 135 * 60, 180, 180 * 60, 00 }, - { 1400, 150 * 60, 180, 180 * 60, 00 }, - { 1350, 165 * 60, 180, 195 * 60, 180 }, - { 1300, 180 * 60, 180, 210 * 60, 180 }, - { 1250, 195 * 60, 180, 225 * 60, 180 }, - { 1200, 210 * 60, 180, 240 * 60, 180 }, - { 1100, 240 * 60, 180, 270 * 60, 180 }, - { 1000, 300 * 60, 360, 300 * 60, 180 }, - { 900, 360 * 60, 360, 360 * 60, 360 }, - { 800, 450 * 60, 540, 450 * 60, 540 }, - { 700, 570 * 60, 720, 570 * 60, 720 }, - { 600, 720 * 60, 900, 720 * 60, 900 }, - { 500, 870 * 60, 900, 870 * 60, 900 } -}; /* Calculate the CNS for a single dive - this only takes the first divecomputer into account. The CNS contributions are summed for dive segments defined by samples. The maximum O2 exposure duration for each @@ -203,9 +174,9 @@ static int const cns_table[][5] = { static double calculate_cns_dive(const struct dive *dive) { int n; - size_t j; const struct divecomputer *dc = &dive->dc; double cns = 0.0; + double rate; /* Calculate the CNS for each sample in this dive and sum them */ for (n = 1; n < dc->samples; n++) { int t; @@ -233,12 +204,10 @@ static double calculate_cns_dive(const struct dive *dive) /* Don't increase CNS when po2 below 500 matm */ if (po2i <= 500) continue; - /* Find the table-row for calculating the maximum exposure at this PO2 */ - for (j = 1; j < sizeof(cns_table) / (sizeof(int) * NO_COLUMNS); j++) - if (po2i > cns_table[j][PO2VAL]) - break; - /* Increment CNS with simple linear interpolation: 100 * time / (single-exposure-time + delta-PO2 * single-slope) */ - cns += (double)t / ((double)cns_table[j][SINGLE_EXP] - ((double)po2i - (double)cns_table[j][PO2VAL]) * (double)cns_table[j][SINGLE_SLOPE] / 10.0) * 100; + + // This formula is the result of fitting two lines to the Log of the NOAA CNS table + rate = po2i <= 1500 ? exp(-11.7853 + 0.00193873 * po2i) : exp(-23.6349 + 0.00980829 * po2i); + cns += (double) t * rate * 1000.0; } return cns; } |