single diff measurement question (intersection of two structs via prns)

sdiff_empty.c

// Compiles with gcc -O0 sdiff_empty.c
// After running your sdiff function once, it will run
// a second time on canned data and compare your results with
// known outputs.

#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <stdio.h>
#include <inttypes.h>
#include <assert.h>
#include <stdlib.h>

// Note: this is a bad thing to do generally.
// http://stackoverflow.com/questions/3437404/min-and-max-in-c
#define MIN(X, Y) (((X) < (Y)) ? (X) : (Y))

typedef uint8_t u8;
typedef uint16_t u16;

typedef struct {
  double pseudorange;
  double carrier_phase;
  double doppler;
  double snr;
  u8 prn;
} navigation_measurement_t;

typedef struct {
  double pseudorange;
  double carrier_phase;
  double doppler;
  double snr;
  u8 prn;
} sdiff_t;

/** Given given two lists of undifferenced input observations
 * (navigation_measurement_t), nav_meas_1 and nav_meas_2,
 * constructs the pseudorange, carrier_phase, and
 * Doppler sdiffs (single difference observations) using the
 * intersection of their PRNs.
 *
 * Also:
 *  0. SNR in the output is the min of the SNRs of inputs 1 and 2.
 *  1. `sat_pos` and `sat_vel` are taken from input 1.
 *
 * Returns the number of sdiffs in the intersection.
 *
 * \param nav_meas1_len  Number of measurements in `nav_meas1`
 * \oaram nav_meas1      Array of undifferenced observations
 * \param nav_meas2_len  Number of measurements in `nav_meas2`
 * \oaram nav_meas2      Array of navigation measurements
 * \param sdiff          Single difference observations
 *
 * \return               The number of observations written to `sdiff`
 *
 */
u8 single_diff(u8 nav_meas1_len,
               navigation_measurement_t *nav_meas1,
               u8 nav_meas2_len,
               navigation_measurement_t *nav_meas2,
               sdiff_t *sdiff)
{
  return 0;
}

int sdiff_test() {
  // Canned measurements
  navigation_measurement_t nm1_1 = {.pseudorange=21930242.933, .carrier_phase=115244233.296, .doppler=2641.315, .snr=48.0, .prn = 1};
  navigation_measurement_t nm2_1 = {.pseudorange=24028321.892, .carrier_phase=126269694.559, .doppler=2702.496, .snr=42.0, .prn = 2};
  navigation_measurement_t nm1_2 = {.pseudorange=21493600.745, .carrier_phase=127759979.261, .doppler=-3919.584, .snr=44.5, .prn = 1};
  navigation_measurement_t nm2_2 = {.pseudorange=28739156.033, .carrier_phase=1035750093.894, .doppler=-1162.682, .snr=41.5, .prn = 4};

  // Array of measurements.
  navigation_measurement_t nms_no_match1[2];
  navigation_measurement_t nms_no_match2[2];

  // Single differences
  sdiff_t sds_out[3];
  memcpy(&nms_no_match1[0], &nm1_1, sizeof(navigation_measurement_t));
  memcpy(&nms_no_match1[1], &nm2_1, sizeof(navigation_measurement_t));
  memcpy(&nms_no_match2[0], &nm1_2, sizeof(navigation_measurement_t));
  memcpy(&nms_no_match2[1], &nm2_2, sizeof(navigation_measurement_t));

  u8 num_match = single_diff(2, nms_no_match1,
                             2, nms_no_match2,
                             sds_out);
  assert(num_match == 1);
  assert(sds_out[0].prn == 1);
  assert((sds_out[0].pseudorange - 436642.188000) < 0.00000001);
  assert((sds_out[0].carrier_phase + 12515745.965000) < 0.00000001);
  assert((sds_out[0].carrier_phase - 6560.899000) < 0.00000001);

  return num_match;
}

int main() {
  // Canned measurements
  navigation_measurement_t nm1_1 = {.pseudorange=21930242.933, .carrier_phase=115244233.296, .doppler=2641.315, .snr=48.0, .prn = 1};
  navigation_measurement_t nm2_1 = {.pseudorange=24028321.892, .carrier_phase=126269694.559, .doppler=2702.496, .snr=42.0, .prn = 2};
  navigation_measurement_t nm1_2 = {.pseudorange=21493600.745, .carrier_phase=127759979.261, .doppler=-3919.584, .snr=44.5, .prn = 1};
  navigation_measurement_t nm2_2 = {.pseudorange=28739156.033, .carrier_phase=1035750093.894, .doppler=-1162.682, .snr=41.5, .prn = 4};

  // Array of measurements.
  navigation_measurement_t nms_no_match1[2];
  navigation_measurement_t nms_no_match2[2];

  // Single differences
  sdiff_t sds_out[3];
  memcpy(&nms_no_match1[0], &nm1_1, sizeof(navigation_measurement_t));
  memcpy(&nms_no_match1[1], &nm2_1, sizeof(navigation_measurement_t));
  memcpy(&nms_no_match2[0], &nm1_2, sizeof(navigation_measurement_t));
  memcpy(&nms_no_match2[1], &nm2_2, sizeof(navigation_measurement_t));

  u8 num_match = single_diff(2, nms_no_match1,
                             2, nms_no_match2,
                             sds_out);
  printf("%d\n", num_match);

  // Validate that it works
  sdiff_test();
}