flightgear/src/Instrumentation/wxradar.cxx

// Wx Radar background texture
//
// Written by Harald JOHNSEN, started May 2005.
// With major amendments by Vivian MEAZZA May 2007
// Ported to OSG by Tim Moore Jun 2007
//
//
// Copyright (C) 2005  Harald JOHNSEN
//
// 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 <osg/Array>
#include <osg/Geometry>
#include <osg/Matrixf>
#include <osg/PrimitiveSet>
#include <osg/StateSet>
#include <osgDB/WriteFile>

#include <simgear/constants.h>
#include <simgear/misc/sg_path.hxx>
#include <simgear/environment/visual_enviro.hxx>
#include <simgear/scene/model/model.hxx>
#include <simgear/structure/exception.hxx>
#include <simgear/misc/sg_path.hxx>
#include <simgear/math/sg_geodesy.hxx>

#include <Main/fg_props.hxx>
#include <Main/globals.hxx>
#include <Cockpit/panel.hxx>
#include <Cockpit/hud.hxx>
#include <AIModel/AIBase.hxx>
#include <AIModel/AIManager.hxx>
#include <AIModel/AIBallistic.hxx>

#include "instrument_mgr.hxx"
#include "od_gauge.hxx"
#include "wxradar.hxx"


// texture name to use in 2D and 3D instruments
static const char *odgauge_name = "Aircraft/Instruments/Textures/od_wxradar.rgb";

wxRadarBg::wxRadarBg ( SGPropertyNode *node) :
    _name(node->getStringValue("name", "radar")),
    _num(node->getIntValue("number", 0)),
    _interval(node->getDoubleValue("update-interval-sec", 1.0)),
    _time( 0.0 ),
    _last_switchKnob( "off" ),
    _sim_init_done ( false ),
    resultTexture( 0 ),
    wxEcho( 0 ),
    _odg( 0 )
{
    const char *tacan_source = node->getStringValue("tacan-source",
            "/instrumentation/tacan");
    _Tacan = fgGetNode(tacan_source, true);
}

wxRadarBg::~wxRadarBg ()
{
}

void
wxRadarBg::init ()
{
    string branch;
    branch = "/instrumentation/" + _name;

    _Instrument = fgGetNode(branch.c_str(), _num, true );
    _serviceable_node = _Instrument->getNode("serviceable", true);

    SGPath tpath(globals->get_fg_root());
    tpath.append("Aircraft/Instruments/Textures/wxecho.rgb");
    // no mipmap or else alpha will mix with pixels on the border of shapes, ruining the effect
    wxEcho = SGLoadTexture2D(tpath.c_str(), false, false);

    _Instrument->setFloatValue("trk", 0.0);
    _Instrument->setFloatValue("tilt", 0.0);
    _Instrument->setStringValue("status","");
    // those properties are used by a radar instrument of a MFD
    // input switch = OFF | TST | STBY | ON
    // input mode = WX | WXA | MAP
    // output status = STBY | TEST | WX | WXA | MAP | blank
    // input lightning = true | false
    // input TRK = +/- n degrees
    // input TILT = +/- n degree
    // input autotilt = true | false
    // input range = n nm (20/40/80)
    // input display-mode = arc | rose | map | plan

    FGInstrumentMgr *imgr = (FGInstrumentMgr *) globals->get_subsystem("instrumentation");
    _odg = (FGODGauge *) imgr->get_subsystem("od_gauge");
    _odg->setSize(256);

    _ai = (FGAIManager*)globals->get_subsystem("ai_model");

    _user_lat_node = fgGetNode("/position/latitude-deg", true);
    _user_lon_node = fgGetNode("/position/longitude-deg", true);
    _user_alt_node = fgGetNode("/position/altitude-ft", true);

    _user_speed_east_fps_node   = fgGetNode("/velocities/speed-east-fps", true);
    _user_speed_north_fps_node  = fgGetNode("/velocities/speed-north-fps", true);

    _tacan_serviceable_node = _Tacan->getNode("serviceable", true);
    _tacan_distance_node    = _Tacan->getNode("indicated-distance-nm", true);
    _tacan_name_node        = _Tacan->getNode("name", true);
    _tacan_bearing_node     = _Tacan->getNode("indicated-bearing-true-deg", true);
    _tacan_in_range_node    = _Tacan->getNode("in-range", true);

    _radar_mode_control_node = _Instrument->getNode("mode-control", true);
    _radar_coverage_node = _Instrument->getNode("limit-deg", true);
    _radar_ref_rng_node = _Instrument->getNode("reference-range-nm", true);
    _radar_coverage_node->setFloatValue(120);
    _radar_ref_rng_node->setDoubleValue(35);

    SGPropertyNode *n = _Instrument->getNode("display-controls", true);
    _radar_weather_node     = n->getNode("WX", true);
    _radar_position_node    = n->getNode("pos", true);
    _radar_data_node        = n->getNode("data", true);
    _radar_centre_node      = n->getNode("centre", true);

    _radar_centre_node->setBoolValue(false);

    _ai_enabled_node = fgGetNode("/sim/ai/enabled", true);

    _x_displacement = 0;
    _y_displacement = 0;
    _x_sym_displacement = 0;
    _y_sym_displacement = 0;

    // OSG geometry setup. The polygons for the radar returns will be
    // stored in a single Geometry. The geometry will have several
    // primitive sets so we can have different kinds of polys and
    // choose a different overall color for each set.
    radarGeode = new osg::Geode;
    osg::StateSet* stateSet = radarGeode->getOrCreateStateSet();
    stateSet->setTextureAttributeAndModes(0, wxEcho.get());
    osg::Geometry* geom = new osg::Geometry;
    geom->setUseDisplayList(false);
    // Initially allocate space for 128 quads
    osg::Vec2Array* vertices = new osg::Vec2Array;
    vertices->setDataVariance(osg::Object::DYNAMIC);
    vertices->reserve(128 * 4);
    geom->setVertexArray(vertices);
    osg::Vec2Array* texCoords = new osg::Vec2Array;
    texCoords->setDataVariance(osg::Object::DYNAMIC);
    texCoords->reserve(128 * 4);
    geom->setTexCoordArray(0, texCoords);
    osg::Vec3Array* colors = new osg::Vec3Array;
    colors->push_back(osg::Vec3(1.0f, 1.0f, 1.0f)); // color of echos
    colors->push_back(osg::Vec3(1.0f, 0.0f, 0.0f)); // arc mask
    colors->push_back(osg::Vec3(0.0f, 0.0f, 0.0f)); // rest of mask
    geom->setColorBinding(osg::Geometry::BIND_PER_PRIMITIVE_SET);
    geom->setColorArray(colors);
    osg::PrimitiveSet* pset = new osg::DrawArrays(osg::PrimitiveSet::QUADS);
    pset->setDataVariance(osg::Object::DYNAMIC);
    geom->addPrimitiveSet(pset);
    pset = new osg::DrawArrays(osg::PrimitiveSet::QUADS);
    pset->setDataVariance(osg::Object::DYNAMIC);
    geom->addPrimitiveSet(pset);
    pset = new osg::DrawArrays(osg::PrimitiveSet::TRIANGLES);
    pset->setDataVariance(osg::Object::DYNAMIC);
    geom->addPrimitiveSet(pset);
    geom->setInitialBound(osg::BoundingBox(osg::Vec3f(-256.0f, -256.0f, 0.0f),
            osg::Vec3f(256.0f, 256.0f, 0.0f)));
    radarGeode->addDrawable(geom);
    _odg->allocRT();
    // Texture in the 2D panel system
    FGTextureManager::addTexture(odgauge_name, _odg->getTexture());

    osg::Camera* camera = _odg->getCamera();
    camera->addChild(radarGeode.get());
}

// Local coordinates for each echo
const osg::Vec3f echoCoords[4] = {
    osg::Vec3f(-.7f, -.7f, 0.0f), osg::Vec3f(.7f, -.7f, 0.0f),
    osg::Vec3f(.7f, .7f, 0.0f), osg::Vec3f(-.7f, .7f, 0.0f)
};

const float symbolSize = 1.0f / 8.0f;
const osg::Vec2f echoTexCoords[4] = {
    osg::Vec2f(0.0f, 0.0f), osg::Vec2f(symbolSize, 0.0f),
    osg::Vec2f(symbolSize, symbolSize), osg::Vec2f(0.0f, symbolSize)
};

// helper
static void
addQuad(osg::Vec2Array* vertices, osg::Vec2Array* texCoords,
        const osg::Matrixf& transform, const osg::Vec2f& texBase)
{
    for (int i = 0; i < 4; i++) {
        const osg::Vec3f coords = transform.preMult(echoCoords[i]);
        texCoords->push_back(texBase + echoTexCoords[i]);
        vertices->push_back(osg::Vec2f(coords.x(), coords.y()));
    }
}

// Rotate by a heading value
static inline
osg::Matrixf wxRotate(float angle)
{
    return osg::Matrixf::rotate(angle, 0.0f, 0.0f, -1.0f);
}

void
wxRadarBg::update (double delta_time_sec)
{
    if ( ! _sim_init_done ) {
        if ( ! fgGetBool("sim/sceneryloaded", false) )
            return;

        _sim_init_done = true;
    }

    if ( !_odg || ! _serviceable_node->getBoolValue() ) {
        _Instrument->setStringValue("status","");
        return;
    }
    _time += delta_time_sec;
    if (_time < _interval)
        return;

    _time = 0.0;

    string switchKnob = _Instrument->getStringValue("switch", "on");
    string modeButton = _Instrument->getStringValue("mode", "wx");
    bool drawLightning = _Instrument->getBoolValue("lightning", true);
    float range_nm = _Instrument->getFloatValue("range", 40.0);
    float range_m = range_nm * SG_NM_TO_METER;

    _user_speed_east_fps = _user_speed_east_fps_node->getDoubleValue();
    _user_speed_north_fps = _user_speed_north_fps_node->getDoubleValue();

    if ( _last_switchKnob != switchKnob ) {
        // since 3D models don't share textures with the rest of the world
        // we must locate them and replace their handle by hand
        // only do that when the instrument is turned on
        //if (last_switchKnob == "off")
        //_odg->set_texture(odgauge_name, resultTexture.get());
        _last_switchKnob = switchKnob;
    }

    _radarEchoBuffer = *sgEnviro.get_radar_echo();
    updateRadar();

    if ( switchKnob == "off" ) {
        _Instrument->setStringValue("status","");
        return;
    } else if ( switchKnob == "stby" ) {
        _Instrument->setStringValue("status","STBY");
        return;
    } else if ( switchKnob == "tst" ) {
        _Instrument->setStringValue("status","TST");
        return;
    }

    // find something interesting to do...
    string display_mode = _Instrument->getStringValue("display-mode", "arc");
    // pretend we have a scan angle bigger then the FOV
    // TODO:check real fov, enlarge if < nn, and do clipping if > mm
    const float fovFactor = 1.45f;
    float view_heading = get_heading() * SG_DEGREES_TO_RADIANS;
    float range = 200.0f / range_nm;
    _Instrument->setStringValue("status", modeButton.c_str());
    osg::Matrixf centerTrans;

    if ( display_mode == "arc" ) {
        centerTrans.makeTranslate(0.0f, -180.0f, 0.0f);
        range = 2*180.0f / range_nm;

    } else if ( display_mode == "map" ) {
        view_heading = 0;

        if (_radar_centre_node->getBoolValue()) {
            _x_displacement =_y_displacement = 0;
        } else {
            _x_displacement += range * _user_speed_east_fps * SG_FPS_TO_KT
                    * delta_time_sec / (60*60);
            _y_displacement += range * _user_speed_north_fps * SG_FPS_TO_KT
                    * delta_time_sec / (60*60);
        }

        SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: displacement "
                << _x_displacement << ", "<<_y_displacement
                << " _user_speed_east_fps * SG_FPS_TO_KT "
                << _user_speed_east_fps * SG_FPS_TO_KT
                << " _user_speed_north_fps * SG_FPS_TO_KT "
                << _user_speed_north_fps * SG_FPS_TO_KT
                << " dt " << delta_time_sec
                << " centre " << _radar_centre_node->getBoolValue());

        centerTrans.makeTranslate(_x_displacement, _y_displacement, 0.0f);

    } else if ( display_mode == "plan" ) {
        // no sense I presume
        view_heading = 0;
    } else {
        // rose
        view_heading = 0;
    }

    range /= SG_NM_TO_METER;

    list_of_SGWxRadarEcho *radarEcho = &_radarEchoBuffer;
    list_of_SGWxRadarEcho::iterator iradarEcho;
    const float LWClevel[] = { 0.1f, 0.5f, 2.1f };
    float dist = 0;
    float size = 0;

    osg::Geometry* geom
            = static_cast<osg::Geometry*>(radarGeode->getDrawable(0));
    osg::Vec2Array* vertices
            = static_cast<osg::Vec2Array*>(geom->getVertexArray());
    osg::Vec2Array* texCoords
            = static_cast<osg::Vec2Array*>(geom->getTexCoordArray(0));
    vertices->clear();
    texCoords->clear();

    // draw the cloud radar echo
    bool drawClouds = _radar_weather_node->getBoolValue();

    if (drawClouds) {
        //we do that in 3 passes, one for each color level
        // this is to 'merge' same colors together
        for (int level = 0; level <= 2; level++) {
            float col = level * symbolSize;

            for (iradarEcho = radarEcho->begin(); iradarEcho != radarEcho->end();
                    ++iradarEcho) {
                int cloudId = (iradarEcho->cloudId);
                bool upgrade = ((cloudId >> 5) & 1);
                float lwc = iradarEcho->LWC + (upgrade ? 1.0f : 0.0f);

                // skip ns
                if (iradarEcho->LWC >= 0.5 && iradarEcho->LWC <= 0.6)
                    continue;

                    if (iradarEcho->lightning || lwc < LWClevel[level]
                            || iradarEcho->aircraft)
                        continue;

                    dist = sgSqrt(iradarEcho->dist);
                    size = iradarEcho->radius * 2.0;

                    if ( dist - size > range_m )
                        continue;

                    dist *= range;
                    size *= range;
                    // Translate echo to proper distance on screen
                    osg::Matrixf distTrans
                            = osg::Matrixf::translate(0.0f, dist * range, 0.0f);
                    // Scale echo
                    osg::Matrixf scaleEcho = osg::Matrixf::scale(size, size, 1.0f);
                    // compute the relative angle from the view direction
                    float angle = calcRelBearing(iradarEcho->bearing, view_heading);

                    // we will rotate the echo quads, this gives a better rendering
                    //const float rot_x = cos (view_heading);
                    //const float rot_y = sin (view_heading);

                    // and apply a fov factor to simulate a greater scan
                    // angle
                    angle *= fovFactor;
                    // Rotate echo into position, and rotate echo to have
                    // a constant orientation towards the
                    // airplane. Compass headings increase in clockwise
                    // direction, while graphics rotations follow
                    // right-hand (counter-clockwise) rule.
                    osg::Matrixf rotEcho = wxRotate(angle);
                    // use different shapes so the display is less boring
                    //float row = symbolSize * (float) (4 + (cloudId & 3) );
                    const osg::Vec2f texBase(col, (symbolSize
                            * (float) (4 + (cloudId & 3))));
                    osg::Matrixf m(scaleEcho * distTrans * rotEcho * centerTrans);
                    addQuad(vertices, texCoords, m, texBase);
                    SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: drawing clouds"
                            << " ID " << iradarEcho->cloudId
                            << " dist" << dist
                            << " view_heading" << view_heading / SG_DEGREES_TO_RADIANS
                            << " heading " << iradarEcho->heading / SG_DEGREES_TO_RADIANS
                            << " angle " << angle / SG_DEGREES_TO_RADIANS);
                }
            }
        }

        // draw lightning echos
        if ( drawLightning ) {
            const osg::Vec2f texBase(3 * symbolSize, 4 * symbolSize);
            for (iradarEcho = radarEcho->begin();
                    iradarEcho != radarEcho->end();
                    ++iradarEcho) {

                if (!iradarEcho->lightning)
                    continue;

                float dist = iradarEcho->dist * range;
                float angle = calcRelBearing(iradarEcho->bearing, view_heading);

                if ( angle > SG_PI )
                    angle -= 2.0*SG_PI;
                if ( angle < - SG_PI )
                    angle += 2.0*SG_PI;

                angle *= fovFactor;
                // Rotate the symbol into position without rotating the
                // symbol itself
                osg::Vec3f trans(0.0f, dist, 0.0f);
                trans = wxRotate(angle).preMult(trans);
                osg::Matrixf m(osg::Matrixf::scale(symbolSize, symbolSize, 1.0)
                        * osg::Matrixf::translate(trans) * centerTrans);
                addQuad(vertices, texCoords, m, texBase);
            }
        }

        //draw aircraft echoes
        if (_radar_position_node->getBoolValue()) {
            const osg::Vec2f texBase(3 * symbolSize, 3 * symbolSize);
            for (iradarEcho = radarEcho->begin();
                    iradarEcho != radarEcho->end();
                    ++iradarEcho) {

                if (!iradarEcho->aircraft)
                    continue;

                dist = iradarEcho->dist * range;

                // calculate relative bearing
                float angle = calcRelBearing(iradarEcho->bearing, view_heading);
                float limit = _radar_coverage_node->getFloatValue();

                if (limit > 180)
                    limit = 180;
                else if (limit < 0)
                    limit = 0;

                // if it's in coverage, draw it
                if (angle >= limit * SG_DEGREES_TO_RADIANS
                        || angle < -limit * SG_DEGREES_TO_RADIANS)
                    continue;

                size = symbolSize * iradarEcho->radius;
                osg::Matrixf m(osg::Matrixf::scale(size, size, 1.0f)
                        * osg::Matrixf::translate(0.0f, dist, 0.0f)
                        * wxRotate(angle) * centerTrans);
                addQuad(vertices, texCoords, m, texBase);
                SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: drawing AI"
                        << " ID " << iradarEcho->cloudId
                        << " dist" << dist
                        << " view_heading" << view_heading / SG_DEGREES_TO_RADIANS
                        << " heading " << iradarEcho->heading / SG_DEGREES_TO_RADIANS
                        << " angle " << angle / SG_DEGREES_TO_RADIANS);
        }
    }

    // Draw aircraft data
    if (_radar_data_node->getBoolValue()) {
        const osg::Vec2f texBase(0, 3 * symbolSize);

        for (iradarEcho = radarEcho->begin();
                iradarEcho != radarEcho->end();
                ++iradarEcho) {

            if (!iradarEcho->aircraft)
                continue;

            dist = iradarEcho->dist;
            dist *= range;
            // calculate relative bearing
            float angle = calcRelBearing(iradarEcho->bearing, view_heading);
            float limit = _radar_coverage_node->getFloatValue();

            if (limit > 180)
                limit = 180;
            else if (limit < 0)
                limit = 0;

            // if it's in coverage, draw it
            if (angle >= limit * SG_DEGREES_TO_RADIANS
                    || angle < -limit * SG_DEGREES_TO_RADIANS)
                continue;

            size = symbolSize * 750;
            // Rotate symbol to indicate relative heading   iradarEcho->bearing
            //    - view_heading - angle
            //cout << "heading " << iradarEcho->heading << endl;

            osg::Matrixf m(osg::Matrixf::scale(size, size, 1.0f)
                    * wxRotate(iradarEcho->heading - view_heading - angle)
                    * osg::Matrixf::translate(0.0f, dist, 0.0f)
                    * wxRotate(angle) * centerTrans);
            addQuad(vertices, texCoords, m, texBase);
            SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: drawing data"
                    << " ID " << iradarEcho->cloudId
                    << " view_heading " << view_heading / SG_DEGREES_TO_RADIANS
                    << " bearing " << angle / SG_DEGREES_TO_RADIANS
                    << " dist" << dist
                    << " heading " << iradarEcho->heading / SG_DEGREES_TO_RADIANS
                    << " rotation " << (iradarEcho->heading - view_heading - angle)
                    / SG_DEGREES_TO_RADIANS);
        }
    }

    //draw TACAN symbol
    int mode = _radar_mode_control_node->getIntValue();
    bool inRange = _tacan_in_range_node->getBoolValue();

    if (mode == 1 && inRange) {
        const osg::Vec2f texBase(1 * symbolSize, 3 * symbolSize);
        dist = _tacan_distance_node->getFloatValue() * SG_NM_TO_METER;
        dist *= range;
        // calculate relative bearing
        float angle = calcRelBearing(_tacan_bearing_node->getFloatValue()
                * SG_DEGREES_TO_RADIANS, view_heading);

        // it's always in coverage, so draw it
        osg::Vec3f trans(osg::Vec3f(0.0f, dist, 0.0f) * wxRotate(angle));
        size = symbolSize * 750;
        osg::Matrixf m(osg::Matrixf::scale(size, size, 1.0f)
                * osg::Matrixf::translate(trans) * centerTrans);
        addQuad(vertices, texCoords, m, texBase);
        SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: drawing TACAN"
                << " dist" << dist
                << " view_heading " << view_heading / SG_DEGREES_TO_RADIANS
                << " heading " << _tacan_bearing_node->getDoubleValue()
                << " angle " << angle / SG_DEGREES_TO_RADIANS
                << " size " << size);
    }

    //draw aircraft symbol
    const osg::Vec2f texBase(2 * symbolSize, 3 * symbolSize);
    size = symbolSize * 750;
    view_heading = get_heading() * SG_DEGREES_TO_RADIANS;
    osg::Matrixf m(osg::Matrixf::scale(size, size, 1.0f)
            * wxRotate(view_heading));

    if (display_mode == "map") {
        //cout << "Map Mode " << range << endl;
        m *= osg::Matrixf::translate(range, range, 0.0f);
    }

    m *= centerTrans;

    addQuad(vertices, texCoords, m, texBase);
    osg::DrawArrays* quadPSet
            = static_cast<osg::DrawArrays*>(geom->getPrimitiveSet(0));
    quadPSet->set(osg::PrimitiveSet::QUADS, 0, vertices->size());
    quadPSet->dirty();
        // erase what is out of sight of antenna
        /*
            |\     /|
            | \   / |
            |  \ /  |
            ---------
            |       |
            |       |
            ---------
        */
    osg::DrawArrays* maskPSet
            = static_cast<osg::DrawArrays*>(geom->getPrimitiveSet(1));
    osg::DrawArrays* trimaskPSet
            = static_cast<osg::DrawArrays*>(geom->getPrimitiveSet(2));

    float xOffset = 256.0f, yOffset = 180.0f;
    SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: display mode " << display_mode);

#if 0
        if ( display_mode != "arc" ) {
            xOffset = 240.0f;
        yOffset = 40.0f;
    }
#endif

    if (display_mode == "arc" ) {
        int firstQuadVert = vertices->size();
        texCoords->push_back(osg::Vec2f(0.5f, 0.25f));
        vertices->push_back(osg::Vec2f(-xOffset, 0.0 + yOffset));
        texCoords->push_back(osg::Vec2f(1.0f, 0.25f));
        vertices->push_back(osg::Vec2f(xOffset, 0.0 + yOffset));
        texCoords->push_back(osg::Vec2f(1.0f, 0.5f));
        vertices->push_back(osg::Vec2f(xOffset, 256.0 + yOffset));
        texCoords->push_back(osg::Vec2f(0.5f, 0.5f));
        vertices->push_back(osg::Vec2f(-xOffset, 256.0 + yOffset));
        maskPSet->set(osg::PrimitiveSet::QUADS, firstQuadVert, 4);
        // The triangles aren't supposed to be textured, but there's
        // no need to set up a different Geometry, switch modes,
        // etc. I happen to know that there's a white pixel in the
        // texture at 1.0, 0.0 :)
        float centerY = tan(30 * SG_DEGREES_TO_RADIANS);
        const osg::Vec2f whiteSpot(1.0f, 0.0f);
        vertices->push_back(osg::Vec2f(0.0, 0.0));
        vertices->push_back(osg::Vec2f(-256.0, 0.0));
        vertices->push_back(osg::Vec2f(-256.0, 256.0 * centerY));

        vertices->push_back(osg::Vec2f(0.0, 0.0));
        vertices->push_back(osg::Vec2f(256.0, 0.0));
        vertices->push_back(osg::Vec2f(256.0, 256.0 * centerY));

        vertices->push_back(osg::Vec2f(-256, 0.0));
        vertices->push_back(osg::Vec2f(256.0, 0.0));
        vertices->push_back(osg::Vec2f(-256.0, -256.0));

        vertices->push_back(osg::Vec2f(256, 0.0));
        vertices->push_back(osg::Vec2f(256.0, -256.0));
        vertices->push_back(osg::Vec2f(-256.0, -256.0));

        for (int i = 0; i < 3 * 4; i++)
            texCoords->push_back(whiteSpot);

        trimaskPSet->set(osg::PrimitiveSet::TRIANGLES, firstQuadVert + 4,
                3 * 4);

    } else {
        maskPSet->set(osg::PrimitiveSet::QUADS, 0, 0);
        trimaskPSet->set(osg::PrimitiveSet::TRIANGLES, 0, 0);
    }
    maskPSet->dirty();
    trimaskPSet->dirty();
}

void
wxRadarBg::updateRadar()
{
    bool ai_enabled = _ai_enabled_node->getBoolValue();

    if (!ai_enabled)
        return;

    double radius[] = {0, 1, 1.5, 1.5, 0.001, 0.1, 1.5, 2, 1.5, 1.5};
    bool isDetected = false;

    SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: Loading AI submodels ");
    _radar_list = _ai->get_ai_list();

    if (_radar_list.empty()) {
        SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: Unable to read AI submodel list");
        return;
    }

    SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: AI submodel list size" << _radar_list.size());

    double user_alt = _user_alt_node->getDoubleValue();
    double user_lat = _user_lat_node->getDoubleValue();
    double user_lon = _user_lon_node->getDoubleValue();

    radar_list_iterator radar_list_itr = _radar_list.begin();
    radar_list_iterator end = _radar_list.end();

    while (radar_list_itr != end) {
        double range   = (*radar_list_itr)->_getRange();
        double bearing = (*radar_list_itr)->_getBearing();
        double lat     = (*radar_list_itr)->_getLatitude();
        double lon     = (*radar_list_itr)->_getLongitude();
        double alt     = (*radar_list_itr)->_getAltitude();
        double heading = (*radar_list_itr)->_getHeading();
        int id         = (*radar_list_itr)->getID();
        int type       = (*radar_list_itr)->getType();

        calcRngBrg(user_lat, user_lon, lat, lon, range, bearing);

        SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: AI list size" << _radar_list.size()
                << " type " << type
                << " ID " << id
                << " radar range " << range
                << " bearing " << bearing
                << " alt " << alt);

        bool isVisible = calcRadarHorizon(user_alt, alt, range);
        SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: visible " << isVisible);

        if (isVisible)
            isDetected = calcMaxRange(type, range);

        //(float _heading, float _alt, float _radius, float _dist, double _LWC, bool _lightning,
        // int _cloudId, bool _aircraft)
        if (isDetected)
            _radarEchoBuffer.push_back(SGWxRadarEcho (
                    bearing * SG_DEGREES_TO_RADIANS,
                    alt,
                    radius[type] * 120,
                    range * SG_NM_TO_METER,
                    heading * SG_DEGREES_TO_RADIANS,
                    1,
                    false,
                    id,
                    true));

        ++radar_list_itr;
    }
}

bool
wxRadarBg::calcRadarHorizon(double user_alt, double alt, double range)
{
    // Radar Horizon  = 1.23(ht^1/2 + hr^1/2),

    //don't allow negative altitudes (an approximation - yes altitudes can be negative)

    if (user_alt < 0)
        user_alt = 0;

    if (alt < 0)
        alt = 0;

    double radarhorizon = 1.23 * (sqrt(alt) + sqrt(user_alt));
    SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: horizon " << radarhorizon);

    return radarhorizon >= range;
}

bool
wxRadarBg::calcMaxRange(int type, double range)
{
    //The Radar Equation:
    //
    // MaxRange^4 = (TxPower * AntGain^2 * lambda^2 * sigma)/((constant) * MDS)
    //
    // Where (constant) = (4*pi)3 and MDS is the Minimum Detectable Signal power.
    //
    // For a given radar we can assume that the only variable is sigma,
    // the target radar cross section.
    //
    // Here, we will use a normalised rcs (sigma) for a standard target and assume that this
    // will provide a maximum range of 35nm;
    //
    // The reference range is adjustable at runtime

    double sigma[] = {0, 1, 100, 100, 0.001, 0.1, 100, 100, 1, 1};
    double constant = _radar_ref_rng_node->getDoubleValue();

    if (constant <= 0)
        constant = 35;

    double maxrange = constant * pow(sigma[type], 0.25);

    SG_LOG(SG_GENERAL, SG_DEBUG, "Radar: max range " << maxrange);

    return maxrange >= range;
}

void
wxRadarBg::calcRngBrg(double lat, double lon, double lat2, double lon2, double &range,
                       double &bearing ) const
{
    double az2, distance;

    // calculate the bearing and range of the second pos from the first
    geo_inverse_wgs_84(lat, lon, lat2, lon2, &bearing, &az2, &distance);

    range = distance *= SG_METER_TO_NM;
}

float
wxRadarBg::calcRelBearing(float bearing, float heading)
{
    float angle = bearing - heading;

    if (angle > SG_PI)
        angle -= 2.0*SG_PI;

    if (angle < -SG_PI)
        angle += 2.0*SG_PI;

    return angle;
}