Ramer-Douglas-Peucker路径简化算法

Question

我在阅读这篇文章后实现了路径简化算法:

http://losingfight.com/blog/2011/05/30/how-to-implement-a-vector-brush/

它对我来说非常适合为我的游戏生成优化的关卡几何体.但是,我现在正在使用它来清理一个*寻路路径,它有一个奇怪的边缘情况,惨遭失败.

这是它工作的截图 - 优化从红色圆圈到蓝色圆圈的路径.淡绿色线是a*输出,浅白色线是优化路径.

这是一个失败的屏幕截图:

这是我的代码.我将文章中的ObjC代码改编为c ++

注意:vec2fvec是a std::vector< vec2<float> >,'real'只是一个typedef'd float.

       void rdpSimplify( const vec2fvec &in, vec2fvec &out, real threshold )
{
    if ( in.size() <= 2 )
    {
        out = in;
        return;
    }

    //
    //  Find the vertex farthest from the line defined by the start and and of the path
    //

    real maxDist = 0;
    size_t maxDistIndex = 0;      
    LineSegment line( in.front(), in.back() );

    for ( vec2fvec::const_iterator it(in.begin()),end(in.end()); it != end; ++it )
    {
        real dist = line.distance( *it );
        if ( dist > maxDist )
        {
            maxDist = dist;
            maxDistIndex = it - in.begin();
        }
    }

    //
    //  If the farhtest vertex is greater than our threshold, we need to
    //  partition and optimize left and right separately
    //

    if ( maxDist > threshold )
    {
        //
        //  Partition 'in' into left and right subvectors, and optimize them
        //

        vec2fvec left( maxDistIndex+1 ),
                 right( in.size() - maxDistIndex ),
                 leftSimplified,
                 rightSimplified;

        std::copy( in.begin(), in.begin() + maxDistIndex + 1, left.begin() );
        std::copy( in.begin() + maxDistIndex, in.end(), right.begin() );

        rdpSimplify(left, leftSimplified, threshold );
        rdpSimplify(right, rightSimplified, threshold );

        //
        //  Stitch optimized left and right into 'out'
        //

        out.resize( leftSimplified.size() + rightSimplified.size() - 1 );
        std::copy( leftSimplified.begin(), leftSimplified.end(), out.begin());
        std::copy( rightSimplified.begin() + 1, rightSimplified.end(), out.begin() + leftSimplified.size() );
    }
    else
    {
        out.push_back( line.a );
        out.push_back( line.b );
    }
}

我真的不知道出了什么问题.我的蜘蛛侠意识说它是在std :: copy调用中......我必须在某些情况下复制垃圾.

编辑:我已经重写了算法,删除任何使用迭代器和std :: copy等.它仍然以完全相同的方式失败.

       void rdpSimplify( const vec2fvec &in, vec2fvec &out, real threshold )
{
    if ( in.size() <= 2 )
    {
        out = in;
        return;
    }

    //
    //  Find the vertex farthest from the line defined by the start and and of the path
    //

    real maxDist = 0;
    size_t maxDistIndex = 0;      
    LineSegment line( in.front(), in.back() );

    for ( size_t i = 0, N = in.size(); i < N; i++ )
    {
        real dist = line.distance( in[i] );
        if ( dist > maxDist )
        {
            maxDist = dist;
            maxDistIndex = i;
        }
    }


    //
    //  If the farthest vertex is greater than our threshold, we need to
    //  partition and optimize left and right separately
    //

    if ( maxDist > threshold )
    {
        //
        //  Partition 'in' into left and right subvectors, and optimize them
        //


        vec2fvec left, right, leftSimplified, rightSimplified;
        for ( size_t i = 0; i < maxDistIndex + 1; i++ ) left.push_back( in[i] );
        for ( size_t i = maxDistIndex; i < in.size(); i++ ) right.push_back( in[i] );


        rdpSimplify(left, leftSimplified, threshold );
        rdpSimplify(right, rightSimplified, threshold );

        //
        //  Stitch optimized left and right into 'out'
        //

        out.clear();
        for ( size_t i = 0, N = leftSimplified.size(); i < N; i++ ) out.push_back(leftSimplified[i]);
        for ( size_t i = 1, N = rightSimplified.size(); i < N; i++ ) out.push_back( rightSimplified[i] );
    }
    else
    {
        out.push_back( line.a );
        out.push_back( line.b );
    }
}

Answer 1

我在你的代码中找不到任何错误。

一些值得尝试的事情：

• 添加一些调试打印语句来检查maxDist失败情况下的内容。它应该非常低，但如果它很高，那么您就知道您的线段距离代码有问题。
• 检查您看到的路径是否确实与算法返回的路径匹配。如果没有，那么您的路径渲染可能有问题？当路径只有两个点时可能是一个错误？
• 通过在算法开始时打印出所有坐标来检查您的输入路径是否符合您的预期。

只要稍微调查一下，应该不会花太长时间就能找到问题的原因。几分钟后，盯着代码进行调试是一种非常糟糕的方法。