Subversion Repositories public iLand

/********************************************************************************************

**    iLand - an individual based forest landscape and disturbance model

**    http://iland.boku.ac.at

**    Copyright (C) 2009-  Werner Rammer, Rupert Seidl

**

**    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 3 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, see <http://www.gnu.org/licenses/>.

********************************************************************************************/

#include "global.h"

#include "standloader.h"

#include "grid.h"

#include "model.h"

#include "resourceunit.h"

#include "speciesset.h"

#include "helper.h"

#include "random.h"

#include "expression.h"

#include "expressionwrapper.h"

#include "environment.h"

#include "csvfile.h"

#include "mapgrid.h"

#include "snapshot.h"

/** @class StandLoader

    @ingroup tools

    loads (initializes) trees for a "stand" from various sources.

    StandLoader initializes trees on the landscape. It reads (usually) from text files, creates the

    trees and distributes the trees on the landscape (on the ResoureceUnit or on a stand defined by a grid).

    See http://iland.boku.ac.at/initialize+trees

  */

// provide a mapping between "Picus"-style and "iLand"-style species Ids

QVector<int> picusSpeciesIds = QVector<int>() << 0 << 1 << 17;

QStringList iLandSpeciesIds = QStringList() << "piab" << "piab" << "fasy";

StandLoader::~StandLoader()

{

    if (mRandom)

        delete mRandom;

    if (mHeightGridResponse)

        delete mHeightGridResponse;

}

void StandLoader::copyTrees()

{

    // we assume that all stands are equal, so wie simply COPY the trees and modify them afterwards

    const Grid<ResourceUnit*> &ruGrid=mModel->RUgrid();

    ResourceUnit **p = ruGrid.begin();

    if (!p)

        throw IException("Standloader: invalid resource unit pointer!");

    ++p; // skip the first...

    const QVector<Tree> &tocopy = mModel->ru()->trees();

    for (; p!=ruGrid.end(); ++p) {

        QRectF rect = (*p)->boundingBox();

        foreach(const Tree& tree, tocopy) {

            Tree &newtree = (*p)->newTree();

            newtree = tree; // copy tree data...

            newtree.setPosition(tree.position()+rect.topLeft());

            newtree.setRU(*p);

            newtree.setNewId();

        }

    }

    if (logLevelInfo()) qDebug() << Tree::statCreated() << "trees loaded / copied.";

}

/** main routine of the stand setup.

*/

void StandLoader::processInit()

{

    GlobalSettings *g = GlobalSettings::instance();

    XmlHelper xml(g->settings().node("model.initialization"));

    QString copy_mode = xml.value("mode", "copy");

    QString type = xml.value("type", "");

    QString  fileName = xml.value("file", "");

    bool height_grid_enabled = xml.valueBool("heightGrid.enabled", false);

    mHeightGridTries = xml.valueDouble("heightGrid.maxTries", 10.);

    QScopedPointer<const MapGrid> height_grid; // use a QScopedPointer to guarantee that the resource is freed at the end of the processInit() function

    if (height_grid_enabled) {

        QString init_height_grid_file = GlobalSettings::instance()->path(xml.value("heightGrid.fileName"), "init");

        qDebug() << "initialization: using predefined tree heights map" << init_height_grid_file;

        QScopedPointer<const MapGrid> p(new MapGrid(init_height_grid_file, false));

        if (!p->isValid()) {

            throw IException(QString("Error when loading grid with tree heights for stand initalization: file %1 not found or not valid.").arg(init_height_grid_file));

        }

        height_grid.swap(p);

        mInitHeightGrid = height_grid.data();

        QString expr=xml.value("heightGrid.fitFormula", "polygon(x, 0,0, 0.8,1, 1.1, 1, 1.25,0)");

        mHeightGridResponse = new Expression(expr);

        mHeightGridResponse->setLinearizationEnabled(true);

    }

    Tree::resetStatistics();

    // one global init-file for the whole area:

    if (copy_mode=="single") {

        loadInitFile(fileName, type);

        evaluateDebugTrees();

        return;

    }

    // call a single tree init for each resource unit

    if (copy_mode=="unit") {

        foreach( const ResourceUnit *const_ru, g->model()->ruList()) {

            ResourceUnit *ru = const_cast<ResourceUnit*>(const_ru);

            // set environment

            g->model()->environment()->setPosition(ru->boundingBox().center());

            type = xml.value("type", "");

            fileName = xml.value("file", "");

            if (fileName.isEmpty())

                continue;

            loadInitFile(fileName, type, 0, ru);

            if (logLevelInfo()) qDebug() << "loaded" << fileName << "on" << ru->boundingBox() << "," << ru->trees().count() << "trees.";

        }

        evaluateDebugTrees();

        return;

    }

    // map-modus: load a init file for each "polygon" in the standgrid

    if (copy_mode=="map") {

        if (!g->model()->standGrid() || !g->model()->standGrid()->isValid())

            throw IException(QString("Stand-Initialization: model.initialization.mode is 'map' but there is no valid stand grid defined (model.world.standGrid)"));

        QString map_file_name = GlobalSettings::instance()->path(xml.value("mapFileName"), "init");

        CSVFile map_file(map_file_name);

        if (map_file.rowCount()==0)

            throw IException(QString("Stand-Initialization: the map file %1 is empty or missing!").arg(map_file_name));

        int ikey = map_file.columnIndex("id");

        int ivalue = map_file.columnIndex("filename");

        if (ikey<0 || ivalue<0)

            throw IException(QString("Stand-Initialization: the map file %1 does not contain the mandatory columns 'id' and 'filename'!").arg(map_file_name));

        QString file_name;

        for (int i=0;i<map_file.rowCount();i++) {

            int key = map_file.value(i, ikey).toInt();

            if (key>0) {

                file_name = map_file.value(i, ivalue).toString();

                if (logLevelInfo()) qDebug() << "loading" << file_name << "for grid id" << key;

                if (!file_name.isEmpty())

                    loadInitFile(file_name, type, key, NULL);

            }

        }

        mInitHeightGrid = 0;

        evaluateDebugTrees();

        return;

    }

    if (copy_mode=="snapshot") {

        // load a snapshot from a file

        Snapshot shot;

        QString input_db = GlobalSettings::instance()->path(fileName);

        shot.loadSnapshot(input_db);

        return;

    }

    throw IException("StandLoader::processInit: invalid initalization.mode!");

}

void StandLoader::evaluateDebugTrees()

{

    // evaluate debugging

    QString dbg_str = GlobalSettings::instance()->settings().paramValueString("debug_tree");

    int counter=0;

    if (!dbg_str.isEmpty()) {

        if (dbg_str == "debugstamp") {

            qDebug() << "debug_tree = debugstamp: try touching all trees...";

            // try to force an error if a stamp is invalid

            AllTreeIterator at(GlobalSettings::instance()->model());

            double total_offset=0.;

            while (Tree *t=at.next()) {

                total_offset += t->stamp()->offset();

                if (!GlobalSettings::instance()->model()->grid()->isIndexValid(t->positionIndex()))

                    qDebug() << "evaluateDebugTrees: debugstamp: invalid position found!";

            }

            qDebug() << "debug_tree = debugstamp: try touching all trees finished...";

            return;

        }

        TreeWrapper tw;

        Expression dexp(dbg_str, &tw); // load expression dbg_str and enable external model variables

        AllTreeIterator at(GlobalSettings::instance()->model());

        double result;

        while (Tree *t = at.next()) {

            tw.setTree(t);

            result = dexp.execute();

            if (result) {

                t->enableDebugging();

                counter++;

            }

        }

        qDebug() << "evaluateDebugTrees: enabled debugging for" << counter << "trees.";

    }

}

/// load a single init file. Calls loadPicusFile() or loadiLandFile()

/// @param fileName file to load

/// @param type init mode. allowed: "picus"/"single" or "iland"/"distribution"

int StandLoader::loadInitFile(const QString &fileName, const QString &type, int stand_id, ResourceUnit *ru)

{

    QString pathFileName = GlobalSettings::instance()->path(fileName, "init");

    if (!QFile::exists(pathFileName))

        throw IException(QString("StandLoader::loadInitFile: File %1 does not exist!").arg(pathFileName));

    if (type=="picus" || type=="single") {

        if (stand_id>0)

            throw IException(QLatin1String("StandLoader::loadInitFile: initialization type %1 currently not supported for stand initilization mode!")+type);

        return loadPicusFile(pathFileName, ru);

    }

    if (type=="iland" || type=="distribution")

        return loadiLandFile(pathFileName, ru, stand_id);

    throw IException(QLatin1String("StandLoader::loadInitFile: unknown initalization.type:")+type);

}

int StandLoader::loadPicusFile(const QString &fileName, ResourceUnit *ru)

{

    QString content = Helper::loadTextFile(fileName);

    if (content.isEmpty()) {

        qDebug() << "file not found: " + fileName;

        return 0;

    }

    return loadSingleTreeList(content, ru, fileName);

}

/** load a list of trees (given by content) to a resource unit. Param fileName is just for error reporting.

  returns the number of loaded trees.

  */

int StandLoader::loadSingleTreeList(const QString &content, ResourceUnit *ru, const QString &fileName)

{

    if (!ru)

        ru = mModel->ru();

    Q_ASSERT(ru!=0);

    QPointF offset = ru->boundingBox().topLeft();

    SpeciesSet *speciesSet = ru->speciesSet(); // of default RU

    QString my_content(content);

    // cut out the <trees> </trees> part if present

    if (content.contains("<trees>")) {

        QRegExp rx(".*<trees>(.*)</trees>.*");

        rx.indexIn(content, 0);

        if (rx.capturedTexts().count()<1)

            return 0;

        my_content = rx.cap(1).trimmed();

    }

    QStringList lines=my_content.split('\n');

    if (lines.count()<2)

        return 0;

    // drop comments

    while (!lines.isEmpty() && lines.front().startsWith('#') )

        lines.pop_front();

    while (!lines.isEmpty() && lines.last().isEmpty())

        lines.removeLast();

    char sep='\t';

    if (!lines[0].contains(sep))

        sep=';';

    QStringList headers = lines[0].trimmed().split(sep);

    int iID = headers.indexOf("id");

    int iX = headers.indexOf("x");

    int iY = headers.indexOf("y");

    int iBhd = headers.indexOf("bhdfrom");

    if (iBhd<0)

        iBhd = headers.indexOf("dbh");

    double height_conversion = 100.;

    int iHeight = headers.indexOf("treeheight");

    if (iHeight<0) {

        iHeight = headers.indexOf("height");

        height_conversion = 1.; // in meter

    }

    int iSpecies = headers.indexOf("species");

    int iAge = headers.indexOf("age");

    if (iX==-1 || iY==-1 || iBhd==-1 || iSpecies==-1 || iHeight==-1)

        throw IException(QString("Initfile %1 is not valid!\nObligatory columns are: x,y, bhdfrom or dbh, species, treeheight or height.").arg(fileName));

    double dbh;

    bool ok;

    int cnt=0;

    QString speciesid;

    for (int i=1;i<lines.count();i++) {

        QString &line = lines[i];

        dbh = line.section(sep, iBhd, iBhd).toDouble();

        if (dbh<5.)

            continue;

        QPointF f;

        if (iX>=0 && iY>=0) {

           f.setX( line.section(sep, iX, iX).toDouble() );

           f.setY( line.section(sep, iY, iY).toDouble() );

           f+=offset;

        }

        // position valid?

        if (!mModel->heightGrid()->valueAt(f).isValid())

            continue;

        Tree &tree = ru->newTree();

        tree.setPosition(f);

        if (iID>=0)

            tree.setId(line.section(sep, iID, iID).toInt() );

        tree.setDbh(dbh);

        tree.setHeight(line.section(sep, iHeight, iHeight).toDouble()/height_conversion); // convert from Picus-cm to m if necessary

        speciesid = line.section(sep, iSpecies, iSpecies).trimmed();

        int picusid = speciesid.toInt(&ok);

        if (ok) {

            int idx = picusSpeciesIds.indexOf(picusid);

            if (idx==-1)

                throw IException(QString("Loading init-file: invalid Picus-species-id. Species: %1").arg(picusid));

            speciesid = iLandSpeciesIds[idx];

        }

        Species *s = speciesSet->species(speciesid);

        if (!ru || !s)

            throw IException(QString("Loading init-file: either resource unit or species invalid. Species: %1").arg(speciesid));

        tree.setSpecies(s);

        ok = true;

        if (iAge>=0)

           tree.setAge(line.section(sep, iAge, iAge).toInt(&ok), tree.height()); // this is a *real* age

        if (iAge<0 || !ok || tree.age()==0)

           tree.setAge(0, tree.height()); // no real tree age available

        tree.setRU(ru);

        tree.setup();

        cnt++;

    }

    return cnt;

    //qDebug() << "loaded init-file contained" << lines.count() <<"lines.";

    //qDebug() << "lines: " << lines;

}

/** initialize trees on a resource unit based on dbh distributions.

  use a fairly clever algorithm to determine tree positions.

  see http://iland.boku.ac.at/initialize+trees

  @param content tree init file (including headers) in a string

  @param ru resource unit

  @param fileName source file name (for error reporting)

  @return number of trees added

  */

int StandLoader::loadDistributionList(const QString &content, ResourceUnit *ru, int stand_id, const QString &fileName)

{

    if (!ru)

        ru = mModel->ru();

    Q_ASSERT(ru!=0);

    SpeciesSet *speciesSet = ru->speciesSet(); // of default RU

    Q_ASSERT(speciesSet!=0);

    //DebugTimer t("StandLoader::loadiLandFile");

    CSVFile infile;

    infile.loadFromString(content);

    int icount = infile.columnIndex("count");

    int ispecies = infile.columnIndex("species");

    int idbh_from = infile.columnIndex("dbh_from");

    int idbh_to = infile.columnIndex("dbh_to");

    int ihd = infile.columnIndex("hd");

    int iage = infile.columnIndex("age");

    int idensity = infile.columnIndex("density");

    if (icount<0 || ispecies<0 || idbh_from<0 || idbh_to<0 || ihd<0 || iage<0)

        throw IException(QString("load-ini-file: file '%1' containts not all required fields (count, species, dbh_from, dbh_to, hd, age).").arg(fileName));

    mInitItems.clear();

    InitFileItem item;

    bool ok;

    int total_count = 0;

    for (int row=0;row<infile.rowCount();row++) {

        item.count = infile.value(row, icount).toInt();

        total_count += item.count;

        item.dbh_from = infile.value(row, idbh_from).toDouble();

        item.dbh_to = infile.value(row, idbh_to).toDouble();

        item.hd = infile.value(row, ihd).toDouble();

        if (item.hd==0. || item.dbh_from / 100. * item.hd < 4.)

            qWarning() << QString("load init file: file '%1' tries to init trees below 4m height. hd=%2, dbh=%3.").arg(fileName).arg(item.hd).arg(item.dbh_from) ;

            //throw IException(QString("load init file: file '%1' tries to init trees below 4m height. hd=%2, dbh=%3.").arg(fileName).arg(item.hd).arg(item.dbh_from) );

        ok = true;

        if (iage>=0)

            item.age = infile.value(row, iage).toInt(&ok);

        if (iage<0 || !ok)

            item.age = 0;

        item.species = speciesSet->species(infile.value(row, ispecies).toString());

        if (idensity>=0)

            item.density = infile.value(row, idensity).toDouble();

        else

            item.density = 0.;

        if (item.density<-1 || item.density>1)

            throw IException(QString("load-ini-file: invalid value for density. Allowed range is -1..1: '%1' in file '%2', line %3.")

                             .arg(item.density)

                             .arg(fileName)

                             .arg(row));

        if (!item.species) {

            throw IException(QString("load-ini-file: unknown speices '%1' in file '%2', line %3.")

                             .arg(infile.value(row, ispecies).toString())

                             .arg(fileName)

                             .arg(row));

        }

        mInitItems.push_back(item);

    }

    // setup the random distribution

    QString density_func = GlobalSettings::instance()->settings().value("model.initialization.randomFunction", "1-x^2");

    if (logLevelInfo())  qDebug() << "density function:" << density_func;

    if (!mRandom || (mRandom->densityFunction()!= density_func)) {

        if (mRandom)

            delete mRandom;

        mRandom=new RandomCustomPDF(density_func);

        if (logLevelInfo()) qDebug() << "new probabilty density function:" << density_func;

    }

    if (stand_id>0) {

        // execute stand based initialization

        executeiLandInitStand(stand_id);

    } else {

        // exeucte the initialization based on single resource units

        executeiLandInit(ru);

        ru->cleanTreeList();

    }

    return total_count;

}

int StandLoader::loadiLandFile(const QString &fileName, ResourceUnit *ru, int stand_id)

{

    if (!QFile::exists(fileName))

        throw IException(QString("load-ini-file: file '%1' does not exist.").arg(fileName));

    QString content = Helper::loadTextFile(fileName);

    return loadDistributionList(content, ru, stand_id, fileName);

}

// evenlist: tentative order of pixel-indices (within a 5x5 grid) used as tree positions.

// e.g. 12 = centerpixel, 0: upper left corner, ...

int evenlist[25] = { 12, 6, 18, 16, 8, 22, 2, 10, 14, 0, 24, 20, 4,

                     1, 13, 15, 19, 21, 3, 7, 11, 17, 23, 5, 9};

int unevenlist[25] = { 11,13,7,17, 1,19,5,21, 9,23,3,15,

                       6,18,2,10,4,24,12,0,8,14,20,22};

// sort function

bool sortPairLessThan(const QPair<int, double> &s1, const QPair<int, double> &s2)

{

    return s1.second < s2.second;

}

struct SInitPixel {

    double basal_area; // accumulated basal area

    QPoint pixelOffset; // location of the pixel

    ResourceUnit *resource_unit; // pointer to the resource unit the pixel belongs to

    double h_max; // predefined maximum height at given pixel (if available from LIDAR or so)

    SInitPixel(): basal_area(0.), resource_unit(0), h_max(-1.) {}

};

bool sortInitPixelLessThan(const SInitPixel &s1, const SInitPixel &s2)

{

    return s1.basal_area < s2.basal_area;

}

/**

*/

void StandLoader::executeiLandInit(ResourceUnit *ru)

{

    QPointF offset = ru->boundingBox().topLeft();

    QPoint offsetIdx = GlobalSettings::instance()->model()->grid()->indexAt(offset);

    // a multimap holds a list for all trees.

    // key is the index of a 10x10m pixel within the resource unit

    QMultiMap<int, int> tree_map;

    //QHash<int,SInitPixel> tcount;

    QVector<QPair<int, double> > tcount; // counts

    for (int i=0;i<100;i++)

        tcount.push_back(QPair<int,double>(i,0.));

    int key;

    double rand_val, rand_fraction;

    int total_count = 0;

    foreach(const InitFileItem &item, mInitItems) {

        rand_fraction = fabs(double(item.density));

        for (int i=0;i<item.count;i++) {

            // create trees

            int tree_idx = ru->newTreeIndex();

            Tree &tree = ru->trees()[tree_idx]; // get reference to modify tree

            tree.setDbh(nrandom(item.dbh_from, item.dbh_to));

            tree.setHeight(tree.dbh()/100. * item.hd); // dbh from cm->m, *hd-ratio -> meter height

            tree.setSpecies(item.species);

            if (item.age<=0)

                tree.setAge(0,tree.height());

            else

                tree.setAge(item.age, tree.height());

            tree.setRU(ru);

            tree.setup();

            total_count++;

            // calculate random value. "density" is from 1..-1.

            rand_val = mRandom->get();

            if (item.density<0)

                rand_val = 1. - rand_val;

            rand_val = rand_val * rand_fraction + drandom()*(1.-rand_fraction);

            // key: rank of target pixel

            // first: index of target pixel

            // second: sum of target pixel

            key = limit(int(100*rand_val), 0, 99); // get from random number generator

            tree_map.insert(tcount[key].first, tree_idx); // store tree in map

            tcount[key].second+=tree.basalArea(); // aggregate the basal area for each 10m pixel

            if ( (total_count < 20 && i%2==0)

                || (total_count<100 && i%10==0 )

                || (i%30==0) ) {

                qSort(tcount.begin(), tcount.end(), sortPairLessThan);

            }

        }

        qSort(tcount.begin(), tcount.end(), sortPairLessThan);

    }

    int bits, index, pos;

    int c;

    QList<int> trees;

    QPoint tree_pos;

    for (int i=0;i<100;i++) {

        trees = tree_map.values(i);

        c = trees.count();

        QPointF pixel_center = ru->boundingBox().topLeft() + QPointF((i/10)*10. + 5., (i%10)*10. + 5.);

        if (!mModel->heightGrid()->valueAt(pixel_center).isValid()) {

            // no trees on that pixel: let trees die

            foreach(int tree_idx, trees) {

                ru->trees()[tree_idx].die();

            }

            continue;

        }

        bits = 0;

        index = -1;

        double r;

        foreach(int tree_idx, trees) {

            if (c>18) {

                index = (index + 1)%25;

            } else {

                int stop=1000;

                index = 0;

                do {

                    //r = drandom();

                    //if (r<0.5)  // skip position with a prob. of 50% -> adds a little "noise"

                    //    index++;

                    //index = (index + 1)%25; // increase and roll over

                    // search a random position

                    r = drandom();

                    index = limit(int(25 *  r*r), 0, 24); // use rnd()^2 to search for locations -> higher number of low indices (i.e. 50% of lookups in first 25% of locations)

                } while (isBitSet(bits, index)==true && stop--);

                if (!stop)

                    qDebug() << "executeiLandInit: found no free bit.";

                setBit(bits, index, true); // mark position as used

            }

            // get position from fixed lists (one for even, one for uneven resource units)

            pos = ru->index()%2?evenlist[index]:unevenlist[index];

            tree_pos = offsetIdx  // position of resource unit

                       + QPoint(5*(i/10), 5*(i%10)) // relative position of 10x10m pixel

                       + QPoint(pos/5, pos%5); // relative position within 10x10m pixel

            //qDebug() << tree_no++ << "to" << index;

            ru->trees()[tree_idx].setPosition(tree_pos);

        }

    }

}

// provide a hashing function for the QPoint type (needed from stand init function below)

inline uint qHash(const QPoint &key)

 {

     return qHash(key.x()) ^ qHash(key.y());

 }

// Initialization routine based on a stand map.

// Basically a list of 10m pixels for a given stand is retrieved

// and the filled with the same procedure as the resource unit based init

// see http://iland.boku.ac.at/initialize+trees

void StandLoader::executeiLandInitStand(int stand_id)

{

    const MapGrid *grid = GlobalSettings::instance()->model()->standGrid();

    // get a list of positions of all pixels that belong to our stand

    QList<int> indices = grid->gridIndices(stand_id);

    if (indices.isEmpty()) {

        qDebug() << "stand" << stand_id << "not in project area. No init performed.";

        return;

    }

    // a multiHash holds a list for all trees.

    // key is the location of the 10x10m pixel

    QMultiHash<QPoint, int> tree_map;

    QList<SInitPixel> pixel_list; // working list of all 10m pixels

    pixel_list.reserve(indices.size());

    foreach (int i, indices) {

       SInitPixel p;

       p.pixelOffset = grid->grid().indexOf(i); // index in the 10m grid

       p.resource_unit = GlobalSettings::instance()->model()->ru( grid->grid().cellCenterPoint(p.pixelOffset));

       if (mInitHeightGrid)

           p.h_max = mInitHeightGrid->grid().constValueAtIndex(p.pixelOffset);

       pixel_list.append(p);

    }

    double area_factor = grid->area(stand_id) / 10000.;

    int key=0;

    double rand_val, rand_fraction;

    int total_count = 0;

    int total_tries = 0;

    int total_misses = 0;

    if (mInitHeightGrid && !mHeightGridResponse)

        throw IException("executeiLandInitStand: trying to initialize with height grid but without response function.");

    foreach(const InitFileItem &item, mInitItems) {

        rand_fraction = fabs(double(item.density));

        int count = item.count * area_factor + 0.5; // round

        double init_max_height = item.dbh_to/100. * item.hd;

        for (int i=0;i<count;i++) {

            bool found = false;

            int tries = mHeightGridTries;

            while (!found &&--tries) {

                // calculate random value. "density" is from 1..-1.

                rand_val = mRandom->get();

                if (item.density<0)

                    rand_val = 1. - rand_val;

                rand_val = rand_val * rand_fraction + drandom()*(1.-rand_fraction);

                ++total_tries;

                // key: rank of target pixel

                key = limit(int(pixel_list.count()*rand_val), 0, pixel_list.count()-1); // get from random number generator

                if (mInitHeightGrid) {

                    // calculate how good the selected pixel fits w.r.t. the predefined height

                    double p_value = pixel_list[key].h_max>0.?mHeightGridResponse->calculate(init_max_height/pixel_list[key].h_max):0.;

                    if (drandom() < p_value)

                        found = true;