From Jon Ellch via bug #5175: Add PPI-GPS protocol dissector patch

Minor changes by me as detailed in the bug's comment #8.


svn path=/trunk/; revision=34956

1 files changed, 624 insertions, 0 deletions

diff --git a/epan/dissectors/packet-ppi-gps.c b/epan/dissectors/packet-ppi-gps.c
new file mode 100644
index 0000000000..d319303c41
--- /dev/null
+++ b/epan/dissectors/packet-ppi-gps.c
@@ -0,0 +1,624 @@
+/* packet-ppi-gps.c
+ * Routines for PPI-GEOLOCATION-GPS  dissection
+ * Copyright 2010, Harris Corp, jellch@harris.com
+ *
+ * $Id$
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1998 Gerald Combs
+ *
+ * Copied from packet-radiotap.c
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <glib.h>
+#include <string.h>
+#include <epan/packet.h>
+#include <epan/ptvcursor.h>
+#include <epan/prefs.h>
+#include <epan/reassemble.h>
+#include <epan/dissectors/packet-ppi-geolocation-common.h>
+enum ppi_geotagging_type {
+    PPI_GEOTAG_GPSFLAGS = 0,
+    PPI_GEOTAG_LAT = 1,
+    PPI_GEOTAG_LON = 2,
+    PPI_GEOTAG_ALT = 3,
+    PPI_GEOTAG_ALT_G = 4,
+    PPI_GEOTAG_GPSTIME = 5,
+    PPI_GEOTAG_FRACTIONALTIME = 6,
+    PPI_GEOTAG_EPH = 7,
+    PPI_GEOTAG_EPV = 8,
+    PPI_GEOTAG_EPT = 9,
+    PPI_GEOTAG_DESCRIPTIONSTR = 28,
+    PPI_GEOTAG_APPID = 29,
+    PPI_GEOTAG_APPDATA = 30,
+    PPI_GEOTAG_EXT = 31
+};
+#define PPI_GPS_MAXTAGLEN  148 /* This increases as fields above are added */
+
+
+/* protocol */
+static int proto_ppi_gps = -1;
+
+static int hf_ppi_gps_version = -1;
+static int hf_ppi_gps_pad = -1;
+static int hf_ppi_gps_length = -1;
+static int hf_ppi_gps_present = -1;
+static int hf_ppi_gps_gpsflags_flags = -1;
+static int hf_ppi_gps_lon = -1;
+static int hf_ppi_gps_lat = -1;
+static int hf_ppi_gps_alt = -1;
+static int hf_ppi_gps_alt_gnd = -1;
+static int hf_ppi_gps_gpstime = -1;
+static int hf_ppi_gps_fractime = -1;
+static int hf_ppi_gps_eph = -1;
+static int hf_ppi_gps_epv = -1;
+static int hf_ppi_gps_ept = -1;
+static int hf_ppi_gps_descr = -1;
+static int hf_ppi_gps_appspecific_num = -1; /* 4-byte tag no */
+static int hf_ppi_gps_appspecific_data = -1; /* 60 byte arbitrary data */
+/* "Present" flags, tese represent decoded-bits in the gui */
+static int hf_ppi_gps_present_gpsflags_flags = -1;
+static int hf_ppi_gps_present_lon = -1;
+static int hf_ppi_gps_present_lat = -1;
+static int hf_ppi_gps_present_alt = -1;
+static int hf_ppi_gps_present_alt_gnd = -1;
+static int hf_ppi_gps_present_gpstime = -1;
+static int hf_ppi_gps_present_fractime = -1;
+static int hf_ppi_gps_present_eph = -1;
+static int hf_ppi_gps_present_epv = -1;
+static int hf_ppi_gps_present_ept = -1;
+static int hf_ppi_gps_present_descr = -1;
+static int hf_ppi_gps_present_appspecific_num = -1;
+static int hf_ppi_gps_present_appspecific_data = -1;
+static int hf_ppi_gps_present_ext = -1;
+
+/* Devicetype flags. not to be confused with "present" flags. These are optional */
+static int hf_ppi_gps_gpsflags_flag0_nofix = -1;
+static int hf_ppi_gps_gpsflags_flag1_gpsfix = -1;
+static int hf_ppi_gps_gpsflags_flag2_diffgps = -1;
+static int hf_ppi_gps_gpsflags_flag3_PPS = -1;
+static int hf_ppi_gps_gpsflags_flag4_RTK = -1;
+static int hf_ppi_gps_gpsflags_flag5_floatRTK = -1;
+static int hf_ppi_gps_gpsflags_flag6_dead_reck = -1;
+static int hf_ppi_gps_gpsflags_flag7_manual = -1;
+static int hf_ppi_gps_gpsflags_flag8_sim = -1;
+
+/* These represent arrow-dropdownthings in the gui */
+static gint ett_ppi_gps = -1;
+static gint ett_ppi_gps_present = -1;
+static gint ett_ppi_gps_gpsflags_flags= -1;
+
+static void
+dissect_ppi_gps(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
+
+void
+proto_register_ppi_gps(void) {
+    /* The following array initializes those header fields declared above to the values displayed */
+    static hf_register_info hf[] = {
+        { &hf_ppi_gps_version,
+            { "Header revision", "ppi_gps.version",
+                FT_UINT8, BASE_DEC, NULL, 0x0,
+                "Version of ppi_gps header format", HFILL } },
+        { &hf_ppi_gps_pad,
+          { "Header pad", "ppi_gps.pad",
+            FT_UINT8, BASE_DEC, NULL, 0x0,
+            "Padding", HFILL } },
+        { &hf_ppi_gps_length,
+          { "Header length", "ppi_gps.length",
+            FT_UINT16, BASE_DEC, NULL, 0x0,
+            "Length of header including version, pad, length and data fields", HFILL } },
+        { &hf_ppi_gps_present, /* these flag fields are composed of a uint32 on the display */
+          { "Present", "ppi_gps.present",
+            FT_UINT32, BASE_HEX, NULL, 0x0, "Bitmask indicating which fields are present", HFILL } },
+
+#define PPI_GPS_MASK_GPSFLAGS		0x00000001
+#define PPI_GPS_MASK_LAT			0x00000002
+#define PPI_GPS_MASK_LON			0x00000004
+#define PPI_GPS_MASK_ALT    	    0x00000008
+#define PPI_GPS_MASK_ALT_G    	    0x00000010
+
+#define PPI_GPS_MASK_GPSTIME 		0x00000020
+#define PPI_GPS_MASK_FRACTIME		0x00000040
+#define PPI_GPS_MASK_EPH			0x00000080
+#define PPI_GPS_MASK_EPV			0x00000100
+#define PPI_GPS_MASK_EPT			0x00000200
+
+#define PPI_GPS_MASK_DESCRSTR		0x10000000
+#define PPI_GPS_MASK_APPID			0x20000000
+#define PPI_GPS_MASK_APPDATA		0x40000000
+#define PPI_GPS_MASK_EXT            0x80000000
+
+        /* Boolean 'present' flags */
+        { &hf_ppi_gps_present_gpsflags_flags, /* followed by a lot of booleans */
+          { "GPSFlags", "ppi_gps.present.gpsflagss",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_GPSFLAGS,
+            "32-bit bitmask indicating type of GPS fix (GPS/INS/software/etc)", HFILL } },
+        { &hf_ppi_gps_present_lat,
+          { "Lat", "ppi_gps.present.lat",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_LAT,
+            "Specifies if the latitude field is present", HFILL } },
+
+        { &hf_ppi_gps_present_lon,
+          { "Lon", "ppi_gps.present.lon",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_LON,
+            "Specifies if the longitude field is present", HFILL } },
+
+        { &hf_ppi_gps_present_alt,
+          { "Alt", "ppi_gps.present.alt",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_ALT,
+            "Specifies if the altitude field is present", HFILL } },
+
+        { &hf_ppi_gps_present_alt_gnd,
+          { "Alt-gnd", "ppi_gps.present.alt_gnd",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_ALT_G,
+            "Specifies if the altitude-g field is present", HFILL } },
+
+        { &hf_ppi_gps_present_gpstime,
+          { "GPStime", "ppi_gps.present.gpstime",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_GPSTIME,
+            "Specifies if the GPS time field is present", HFILL } },
+
+
+        { &hf_ppi_gps_present_fractime,
+          { "fractime", "ppi_gps.present.fractime",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_FRACTIME,
+            "Specifies if the fractional time field is present", HFILL } },
+
+
+        { &hf_ppi_gps_present_eph,
+          { "error_h", "ppi_gps.present.eph",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_EPH,
+            "Specifies if the horizontal error field is present (eph)", HFILL } },
+
+        { &hf_ppi_gps_present_epv,
+          { "error_v", "ppi_gps.present.epv",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_EPV,
+            "Specifies if the vertical error field present (epv)", HFILL } },
+
+
+        { &hf_ppi_gps_present_ept,
+          { "error_t", "ppi_gps.present.ept",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_EPT,
+            "Specifies if the estimed time error field is present (ept)", HFILL } },
+
+        { &hf_ppi_gps_present_descr,
+          { "Description", "ppi_gps.present.descr",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_DESCRSTR,
+            "Specifies if the (ASCII) description is present", HFILL } },
+
+        { &hf_ppi_gps_present_appspecific_num,
+          { "AppId", "ppi_gps.present.appid",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_APPID,
+            "Specifies if the application specific field id is present", HFILL } },
+
+        { &hf_ppi_gps_present_appspecific_data,
+          { "AppData", "ppi_gps.present.appdata",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_APPDATA,
+            "Specifies if the application specific data field  is present", HFILL } },
+
+        { &hf_ppi_gps_present_ext,
+          { "Ext", "ppi_gps.present.ext",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_MASK_EXT,
+            "Specifies if there are any extensions to the header present", HFILL } },
+
+        /* ---Now we get to the actual data fields--- */
+
+        { &hf_ppi_gps_gpsflags_flags,
+          { "GPSFlags", "ppi_gps.gpsflags",
+            FT_UINT32, BASE_HEX, NULL, 0x0, "Bitmask indicating GPS/INS/manual fix", HFILL } },
+        { &hf_ppi_gps_lat,
+          { "Latitude", "ppi_gps.lat",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "Latitude packet was received at", HFILL } },
+        { &hf_ppi_gps_lon,
+          { "Longitude", "ppi_gps.lon",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "Longitude packet was received at", HFILL } },
+        { &hf_ppi_gps_alt,
+          { "Altitude", "ppi_gps.alt",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "Altitude packet was received at", HFILL } },
+        { &hf_ppi_gps_alt_gnd,
+          { "Altitude_gnd", "ppi_gps.alt_gnd",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "Altitude packet was received at (relative to ground)", HFILL } },
+        { &hf_ppi_gps_gpstime,
+          { "GPSTimestamp", "ppi_gps.gpstime",
+            FT_ABSOLUTE_TIME, ABSOLUTE_TIME_UTC, NULL, 0x0,
+            "GPSTimestamp packet was received at", HFILL } },
+        { &hf_ppi_gps_fractime,
+          { "fractional Timestamp", "ppi_gps.fractime",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "fractional GPSTimestamp packet was received at", HFILL } },
+        { &hf_ppi_gps_eph,
+          { "Horizontal Error (m)", "ppi_gps.eph",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "Horizontal margin of error (meters)", HFILL } },
+        { &hf_ppi_gps_epv,
+          { "Vertical Error (m)", "ppi_gps.epv",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "Vertical margin of error (meters) ", HFILL } },
+        { &hf_ppi_gps_ept,
+          { "Time Error (s)", "ppi_gps.ept",
+            FT_DOUBLE, BASE_NONE, NULL, 0x0,
+            "Time margin of error (secs)", HFILL } },
+        { &hf_ppi_gps_descr,
+          { "Description", "ppi_gps.descr",
+            FT_STRING, BASE_NONE, NULL, 0x0,
+            "Description", HFILL } },
+        { &hf_ppi_gps_appspecific_num,
+          { "Application Specific id", "ppi_gps.appid",
+            FT_UINT32, BASE_HEX, NULL, 0x0,
+            "application specific identifier", HFILL } },
+        { &hf_ppi_gps_appspecific_data,
+          { "Application specific data", "ppi_gps.appdata",
+            FT_BYTES, BASE_NONE, NULL, 0x0,
+            "application specific data", HFILL } },
+
+        /* --- moving on to the 'FixType' flags --- */
+#define PPI_GPS_GPSFLAGS_FLAG0_NOFIX		0x00000001
+#define PPI_GPS_GPSFLAGS_FLAG1_GPS		0x00000002
+#define PPI_GPS_GPSFLAGS_FLAG2_DIFFGPS	0x00000004
+#define PPI_GPS_GPSFLAGS_FLAG3_PPS		0x00000008
+#define PPI_GPS_GPSFLAGS_FLAG4_RTK		0x00000010
+#define PPI_GPS_GPSFLAGS_FLAG5_FLOATRTK	0x00000020
+#define PPI_GPS_GPSFLAGS_FLAG6_DEAD_RECK	0x00000040
+#define PPI_GPS_GPSFLAGS_FLAG7_MANUAL	0x00000080
+#define PPI_GPS_GPSFLAGS_FLAG8_SIM		0x00000100
+        { &hf_ppi_gps_gpsflags_flag0_nofix, /* no fix available */
+          { "No fix available", "ppi_gps.gpsflagss.nofix",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG0_NOFIX,
+            "No GPS fix available", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag1_gpsfix, /* GPSfix available */
+          { "GPS provided fix", "ppi_gps.gpsflagss.gps",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG1_GPS,
+            "GPS provided fix", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag2_diffgps, /* Differential GPS fix  available */
+          { "Differential GPS provided fix", "ppi_gps.gpsflagss.diffgps",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG2_DIFFGPS,
+            "DGPS provided fix", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag3_PPS, /* PPS fix  */
+          { "PPS fix", "ppi_gps.gpsflagss.pps",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG3_PPS,
+            " PPS fix ", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag4_RTK, /* RTK fix*/
+          { "RTK fix", "ppi_gps.gpsflagss.rtk",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG4_RTK,
+            "RTK  fix ", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag5_floatRTK, /*float RTK */
+          { "floatRTK fix", "ppi_gps.gpsflagss.frtk",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG5_FLOATRTK,
+            " floatRTK fix ", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag6_dead_reck, /*dead reckoning */
+          { "dead reckoning fix", "ppi_gps.gpsflagss.dead_reck",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG6_DEAD_RECK,
+            "dead reckoning fix ", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag7_manual, /* manual */
+          { "manual fix", "ppi_gps.gpsflagss.manual",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG7_MANUAL,
+            "manual  fix available", HFILL } },
+        { &hf_ppi_gps_gpsflags_flag8_sim, /* simulation */
+          { "simulated fix", "ppi_gps.gpsflagss.simulation",
+            FT_BOOLEAN, 32, NULL, PPI_GPS_GPSFLAGS_FLAG8_SIM,
+            "simulated fix", HFILL } },
+
+    };
+    static gint *ett[] = {
+        &ett_ppi_gps,
+        &ett_ppi_gps_present,
+        &ett_ppi_gps_gpsflags_flags
+    };
+
+    proto_ppi_gps = proto_register_protocol("PPI Geotagging GPS tag decoder", "PPI GPS Decoder", "ppi_gps");
+    proto_register_field_array(proto_ppi_gps, hf, array_length(hf));
+    proto_register_subtree_array(ett, array_length(ett));
+    register_dissector("ppi_gps", dissect_ppi_gps, proto_ppi_gps);
+
+}
+void dissect_ppi_gps(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) {
+    /* These are locals used for processing the current tvb */
+    guint length;
+    guint length_remaining;
+    int offset = 0;
+
+    proto_tree *ppi_gps_tree = NULL;
+    proto_tree *pt, *present_tree = NULL;
+    proto_tree *my_pt, *gpsflags_flags_tree = NULL; /* used for DeviceType bitmask stuff */
+
+    proto_item *ti = NULL;
+
+
+    /* bits */
+    int bit;
+    guint32 present, next_present;
+    /* values actually read out, for displaying */
+    guint32 version, gpsflags_flags;
+    gdouble lat, lon, alt, alt_gnd;
+    nstime_t gps_timestamp;
+    int gps_time_size, already_processed_fractime; /* we use this internally to track if this is a 4 or 8 byte wide timestamp */
+    gdouble eph, epv, ept;
+
+    /* these are temporary intermediate values, used in the individual cases below */
+    guint32 t_lat, t_lon, t_alt, t_alt_gnd;
+    guint32 t_herr, t_verr, t_terr;
+    guint32 t_appspecific_num;
+    /* initialize the timestamp value(s) */
+    gps_timestamp.secs = gps_timestamp.nsecs = gps_time_size = already_processed_fractime = 0;
+
+    /* Clear out stuff in the info column */
+    if (check_col(pinfo->cinfo,COL_INFO))
+        col_clear(pinfo->cinfo,COL_INFO);
+    /* pull out the first three fields of the BASE-GEOTAG-HEADER */
+    version = tvb_get_guint8(tvb, offset);
+    length = tvb_get_letohs(tvb, offset+2);
+    present = tvb_get_letohl(tvb, offset+4);
+
+    if (check_col(pinfo->cinfo, COL_INFO))
+        col_add_fstr(pinfo->cinfo, COL_INFO, "PPI_GPS Capture v%u, Length %u", version, length);
+
+    /* Dissect the packet */
+    if (tree) {
+        ti = proto_tree_add_protocol_format(tree, proto_ppi_gps,
+                                            tvb, 0, length, "PPI GPS Header v%u, Length %u", version, length);
+        ppi_gps_tree= proto_item_add_subtree(ti, ett_ppi_gps);
+        proto_tree_add_uint(ppi_gps_tree, hf_ppi_gps_version, tvb, offset, 1, version);
+        proto_tree_add_item(ppi_gps_tree, hf_ppi_gps_pad, tvb, offset + 1, 1, FALSE);
+        ti = proto_tree_add_uint(ppi_gps_tree, hf_ppi_gps_length, tvb, offset + 2, 2, length);
+    }
+    /* basic length sanity checking */
+    if (length > PPI_GPS_MAXTAGLEN ) {
+        if (tree)
+            proto_item_append_text(ti, "Invalid PPI-GPS length  (got %d, %d max\n)", length, PPI_GPS_MAXTAGLEN);
+        return;
+    }
+    /* no minimum length check, technically zero is valid */
+
+    /* initialize the length of the actual tag contents */
+    length_remaining = length;
+    if (version != 1) {
+        if (tree)
+            proto_item_append_text(ti, "invalid version (got %d, expected 1)", version);
+        return;
+    }
+
+    /*
+     * This only works if there is exactly 1 present
+     * field in the header. This is not a problem as there are currently no extended bitmasks defined.
+     */
+    if (length_remaining < PPI_GEOBASE_MIN_HEADER_LEN) {
+        /*
+         * Base-geotag-header (Radiotap lookalike) is shorter than the fixed-length portion
+         * plus one "present" bitset.
+         */
+        if (tree)
+            proto_item_append_text(ti, " (bogus - minimum length is 8)");
+        return;
+    }
+    /* Subtree for the "present flags" bitfield. */
+    if (tree) {
+        pt = proto_tree_add_uint(ppi_gps_tree, hf_ppi_gps_present, tvb, offset + 4, 4, present);
+        present_tree = proto_item_add_subtree(pt, ett_ppi_gps_present);
+
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_gpsflags_flags, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_lat, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_lon, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_alt, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_alt_gnd, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_gpstime, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_fractime, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_eph, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_epv, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_ept, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_descr, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_appspecific_num, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_appspecific_data, tvb, 4, 4, TRUE);
+        proto_tree_add_item(present_tree, hf_ppi_gps_present_ext, tvb, 4, 4, TRUE);
+    }
+    offset += PPI_GEOBASE_MIN_HEADER_LEN;
+    length_remaining -= PPI_GEOBASE_MIN_HEADER_LEN;
+
+    /* The fixed BASE-GEOTAG-HEADER has been handled at this point. move on to the individual fields */
+    for (; present; present = next_present) {
+        /* clear the least significant bit that is set */
+        next_present = present & (present - 1);
+        /* extract the least significant bit that is set */
+        bit = BITNO_32(present ^ next_present);
+        switch (bit) {
+        case PPI_GEOTAG_GPSFLAGS:
+            if (length_remaining < 4)
+                break;
+            gpsflags_flags =   tvb_get_letohl(tvb, offset); /* retrieve 32-bit gpsflags bitmask (-not- present bitmask) */
+            if (tree) {
+                /* first we add the hex flags line */
+                my_pt = proto_tree_add_uint(ppi_gps_tree, hf_ppi_gps_gpsflags_flags, tvb, offset , 4, gpsflags_flags);
+                /* then we add a subtree */
+                gpsflags_flags_tree = proto_item_add_subtree(my_pt, ett_ppi_gps_gpsflags_flags);
+                /* to pin the individual bits on */
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag0_nofix, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag1_gpsfix, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag2_diffgps, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag3_PPS, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag4_RTK, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag5_floatRTK, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag6_dead_reck, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag7_manual, tvb, offset, 4, TRUE);
+                proto_tree_add_item(gpsflags_flags_tree, hf_ppi_gps_gpsflags_flag8_sim, tvb, offset, 4, TRUE);
+            }
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_LAT:
+            if (length_remaining < 4)
+                break;
+            t_lat = tvb_get_letohl(tvb, offset);
+            lat =  fixed3_7_to_gdouble(t_lat);
+            if (tree)
+                proto_tree_add_double(ppi_gps_tree, hf_ppi_gps_lat, tvb, offset, 4, lat);
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_LON:
+            if (length_remaining < 4)
+                break;
+            t_lon = tvb_get_letohl(tvb, offset);
+            lon =  fixed3_7_to_gdouble(t_lon);
+            if (tree)
+                proto_tree_add_double(ppi_gps_tree, hf_ppi_gps_lon, tvb, offset, 4, lon);
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_ALT:
+            if (length_remaining < 4)
+                break;
+            t_alt = tvb_get_letohl(tvb, offset);
+            alt = fixed6_4_to_gdouble(t_alt);
+            if (tree)
+                proto_tree_add_double(ppi_gps_tree, hf_ppi_gps_alt, tvb, offset, 4, alt);
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_ALT_G:
+            if (length_remaining < 4)
+                break;
+            t_alt_gnd = tvb_get_letohl(tvb, offset);
+            alt_gnd = fixed6_4_to_gdouble(t_alt_gnd);
+            if (tree)
+                proto_tree_add_double(ppi_gps_tree, hf_ppi_gps_alt_gnd, tvb, offset, 4, alt_gnd);
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_GPSTIME:
+            if (length_remaining < 4)
+                break;
+            gps_timestamp.secs =    tvb_get_letohl(tvb, offset);
+            gps_timestamp.nsecs = 0;
+            gps_time_size = 4;
+            /* This is somewhat tricky, inside the GPSTIME case we test if the optional fractional time */
+            /* is present. If so, we pull it out, and combine it with GPSTime. */
+            /* If we do this, we set already_processed_fractime to avoid hitting it below */
+            if (length_remaining < 4 && (present & PPI_GPS_MASK_FRACTIME))
+                break;
+            else if (present & PPI_GPS_MASK_FRACTIME) {
+                gps_timestamp.nsecs =  tvb_get_letohl(tvb, offset + 4); /* manually offset seconds */
+                already_processed_fractime = 1;
+                gps_time_size = 8;
+            }
+            if (tree) {
+                proto_tree_add_time(ppi_gps_tree, hf_ppi_gps_gpstime, tvb, offset, gps_time_size, &gps_timestamp);
+            }
+            offset += gps_time_size;
+            length_remaining -= gps_time_size;
+            break;
+        case  PPI_GEOTAG_FRACTIONALTIME:
+            if (length_remaining < 4)
+                break;
+            if (already_processed_fractime)
+                break;
+            break;
+        case  PPI_GEOTAG_EPH:
+            if (length_remaining < 4)
+                break;
+            t_herr = tvb_get_letohl(tvb, offset);
+            eph  =  fixed3_6_to_gdouble(t_herr);
+            if (tree)
+                proto_tree_add_double(ppi_gps_tree, hf_ppi_gps_eph, tvb, offset, 4, eph);
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_EPV:
+            if (length_remaining < 4)
+                break;
+            t_verr = tvb_get_letohl(tvb, offset);
+            epv  =  fixed3_6_to_gdouble(t_verr);
+            if (tree)
+                proto_tree_add_double(ppi_gps_tree, hf_ppi_gps_epv, tvb, offset, 4, epv);
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_EPT:
+            if (length_remaining < 4)
+                break;
+            t_terr = tvb_get_letohl(tvb, offset);
+            ept  =  ns_counter_to_gdouble(t_terr);
+            if (tree)
+                proto_tree_add_double(ppi_gps_tree, hf_ppi_gps_ept, tvb, offset, 4, ept);
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_DESCRIPTIONSTR:
+            if (length_remaining < 32)
+                break;
+            if (tree)
+                proto_tree_add_item(ppi_gps_tree, hf_ppi_gps_descr, tvb, offset, 32,  FALSE);
+            offset+=32;
+            length_remaining-=32;
+            break;
+        case  PPI_GEOTAG_APPID:
+            if (length_remaining < 4)
+                break;
+            t_appspecific_num  = tvb_get_letohl(tvb, offset); /* application specific parsers may switch on this later */
+            if (tree) {
+                proto_tree_add_uint(ppi_gps_tree, hf_ppi_gps_appspecific_num, tvb, offset, 4, t_appspecific_num);
+            }
+            offset+=4;
+            length_remaining-=4;
+            break;
+        case  PPI_GEOTAG_APPDATA:
+            if (length_remaining < 60)
+                break;
+            if (tree) {
+                proto_tree_add_item(ppi_gps_tree, hf_ppi_gps_appspecific_data, tvb, offset, 60,  FALSE);
+            }
+            offset+=60;
+            length_remaining-=60;
+            break;
+
+            /*
+             * This indicates a field whose size we do not know, so we cannot proceed.
+             */
+        default:
+            next_present = 0; /* this will terminate the loop */
+            proto_tree_add_text(ppi_gps_tree, tvb, offset, 0,  "Error: PPI-GEOLOCATION-GPS: unknown bit (%d) set in present field.\n", bit);
+            continue;
+        } /* switch (bit) */
+
+    } /* (for present..)*/
+
+    /* If there was any post processing of the elements, it could happen here. */
+    return;
+}
+
+/*
+ * Editor modelines
+ *
+ * Local Variables:
+ * c-basic-offset: 4
+ * tab-width: 8
+ * indent-tabs-mode: nil
+ * End:
+ *
+ * ex: set shiftwidth=4 tabstop=8 expandtab
+ * :indentSize=4:tabSize=8:noTabs=true:
+ */
+
+
+