Utilizing low-cost unmanned aerial vehicles (UAV) to build orthophotos and Digital Surface Models (DSM)

Britta Ricker, PhD

USGS Brown bag Seminar Dec. 16, 2015

About my research

Outline

  • Harnessing the hype
  • Brief History
  • Planning a project
  • Mapping products
  • Additional Considerations
  • Future

How can we

harness the hype

of accessible technology

to make maps!

image processing

photogrammetry science of making measurements from photographs, especially for recovering the exact positions of surface points.

http://www.cs.columbia.edu/~jebara/htmlpapers/SFM/node4.html

 

and http://www.cs.columbia.edu/~jebara/htmlpapers/SFM/sfm.html

 

 

Photogrammetry 

stability

accuracy

implementation

Structure from Motion

Evolved out of computer vision

Ties images together

More images = more tie points

 

scale of image

tied by metadata

tied by pixel values

// C++
#include <math.h>
#include <sstream>
#include <fstream>

// This
#include "OdmOrthoPhoto.hpp"

std::ostream & operator<< (std::ostream &os, const WorldPoint &worldPoint)
{
    return os << worldPoint.eastInteger_ + worldPoint.eastFractional_ << " " << worldPoint.northInteger_ + worldPoint.northFractional_;
}

std::istream & operator>> (std::istream &is,  WorldPoint &worldPoint)
{
    is >> worldPoint.eastInteger_;
    // Check if east coordinate is given as rational.
    if('.' == is.peek())
    {
        is >> worldPoint.eastFractional_;
    }
    else
    {
        worldPoint.eastFractional_ = 0.0f;
    }
    
    is >> worldPoint.northInteger_;
    // Check if north coordinate is given as rational.
    if('.' == is.peek())
    {
        is >> worldPoint.northFractional_;
    }
    else
    {
        worldPoint.northFractional_ = 0.0f;
    }

    return is;
}

OdmOrthoPhoto::OdmOrthoPhoto()
    :log_(false)
{
    inputFile_ = "";
    inputGeoRefFile_ = "";
    outputFile_ = "ortho.jpg";
    logFile_    = "log.txt";
    outputCornerFile_ = "";

    resolution_ = 0.0f;

    boundaryDefined_ = false;
    boundaryPoint1_[0] = 0.0f; boundaryPoint1_[1] = 0.0f;
    boundaryPoint2_[0] = 0.0f; boundaryPoint2_[1] = 0.0f;
    boundaryPoint3_[0] = 0.0f; boundaryPoint3_[1] = 0.0f;
    boundaryPoint4_[0] = 0.0f; boundaryPoint4_[1] = 0.0f;
}

OdmOrthoPhoto::~OdmOrthoPhoto()
{
}

int OdmOrthoPhoto::run(int argc, char *argv[])
{
    try
    {
        parseArguments(argc, argv);
        createOrthoPhoto();
    }
    catch (const OdmOrthoPhotoException& e)
    {
        log_.setIsPrintingInCout(true);
        log_ << e.what() << "\n";
        log_.print(logFile_);
        return EXIT_FAILURE;
    }
    catch (const std::exception& e)
    {
        log_.setIsPrintingInCout(true);
        log_ << "Error in OdmOrthoPhoto:\n";
        log_ << e.what() << "\n";
        log_.print(logFile_);
        return EXIT_FAILURE;
    }
    catch (...)
    {
        log_.setIsPrintingInCout(true);
        log_ << "Unknown error, terminating:\n";
        log_.print(logFile_);
        return EXIT_FAILURE;
    }
    
    log_.print(logFile_);
    
    return EXIT_SUCCESS;
}

void OdmOrthoPhoto::parseArguments(int argc, char *argv[])
{
    logFile_ = std::string(argv[0]) + "_log.txt";
    log_ << logFile_ << "\n\n";
    
    // If no arguments were passed, print help.
    if (argc == 1)
    {
        printHelp();
    }
    
    log_ << "Arguments given\n";
    for(int argIndex = 1; argIndex < argc; ++argIndex)
    {
        log_ << argv[argIndex] << '\n';
    }
    
    log_ << '\n';
    for(int argIndex = 1; argIndex < argc; ++argIndex)
    {
        // The argument to be parsed.
        std::string argument = std::string(argv[argIndex]);
        
        if(argument == "-help")
        {
            printHelp();
        }
        else if(argument == "-resolution")
        {
            ++argIndex;
            if (argIndex >= argc)
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' expects 1 more input following it, but no more inputs were provided.");
            }
            std::stringstream ss(argv[argIndex]);
            ss >> resolution_;
            log_ << "Resolution count was set to: " << resolution_ << "pixels/meter\n";
        }
        else if(argument == "-boundary")
        {
            if(argIndex+8 >= argc)
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' expects 8 more input following it, but no more inputs were provided.");
            }

            std::stringstream ss;
            ss << argv[argIndex+1] << " " << argv[argIndex+2] << " " << argv[argIndex+3] << " " << argv[argIndex+4] << " " << argv[argIndex+5] << " " << argv[argIndex+6] << " " << argv[argIndex+7] << " " << argv[argIndex+8];
            ss >> worldPoint1_ >> worldPoint2_ >> worldPoint3_ >> worldPoint4_;
            boundaryDefined_ = true;

            argIndex += 8;

            log_ << "Boundary point 1 was set to: " << worldPoint1_ << '\n';
            log_ << "Boundary point 2 was set to: " << worldPoint2_ << '\n';
            log_ << "Boundary point 3 was set to: " << worldPoint3_ << '\n';
            log_ << "Boundary point 4 was set to: " << worldPoint4_ << '\n';
        }
        else if(argument == "-boundaryMinMax")
        {
            if(argIndex+4 >= argc)
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' expects 4 more input following it, but no more inputs were provided.");
            }

            std::stringstream ss;
            ss << argv[argIndex+1] << " " << argv[argIndex+2] << " " << argv[argIndex+3] << " " << argv[argIndex+4];
            ss >> worldPoint1_ >> worldPoint3_;
            boundaryDefined_ = true;

            // Set the other world points as the other two corners.
            worldPoint2_.eastFractional_  = worldPoint1_.eastFractional_;
            worldPoint2_.eastInteger_     = worldPoint1_.eastInteger_;
            worldPoint2_.northFractional_ = worldPoint3_.northFractional_;
            worldPoint2_.northInteger_    = worldPoint3_.northInteger_;
            
            worldPoint4_.eastFractional_  = worldPoint3_.eastFractional_;
            worldPoint4_.eastInteger_     = worldPoint3_.eastInteger_;
            worldPoint4_.northFractional_ = worldPoint1_.northFractional_;
            worldPoint4_.northInteger_    = worldPoint1_.northInteger_;

            argIndex += 4;

            log_ << "Boundary point 1 was set to: " << worldPoint1_ << '\n';
            log_ << "Boundary point 2 was set to: " << worldPoint2_ << '\n';
            log_ << "Boundary point 3 was set to: " << worldPoint3_ << '\n';
            log_ << "Boundary point 4 was set to: " << worldPoint4_ << '\n';
        }
        else if(argument == "-verbose")
        {
            log_.setIsPrintingInCout(true);
        }
        else if (argument == "-logFile")
        {
            ++argIndex;
            if (argIndex >= argc)
            {
                throw OdmOrthoPhotoException("Missing argument for '" + argument + "'.");
            }
            logFile_ = std::string(argv[argIndex]);
            std::ofstream testFile(logFile_.c_str());
            if (!testFile.is_open())
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' has a bad value.");
            }
            log_ << "Log file path was set to: " << logFile_ << "\n";
        }
        else if(argument == "-inputFile")
        {
            argIndex++;
            if (argIndex >= argc)
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' expects 1 more input following it, but no more inputs were provided.");
            }
            inputFile_ = std::string(argv[argIndex]);
            log_ << "Reading textured mesh from: " << inputFile_ << "\n";
        }
        else if(argument == "-inputGeoRefFile")
        {
            argIndex++;
            if (argIndex >= argc)
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' expects 1 more input following it, but no more inputs were provided.");
            }
            inputGeoRefFile_ = std::string(argv[argIndex]);
            log_ << "Reading georef from: " << inputGeoRefFile_ << "\n";
        }
        else if(argument == "-outputFile")
        {
            argIndex++;
            if (argIndex >= argc)
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' expects 1 more input following it, but no more inputs were provided.");
            }
            outputFile_ = std::string(argv[argIndex]);
            log_ << "Writing output to: " << outputFile_ << "\n";
        }
        else if(argument == "-outputCornerFile")
        {
            argIndex++;
            if (argIndex >= argc)
            {
                throw OdmOrthoPhotoException("Argument '" + argument + "' expects 1 more input following it, but no more inputs were provided.");
            }
            outputCornerFile_ = std::string(argv[argIndex]);
            log_ << "Writing corners to: " << outputCornerFile_ << "\n";
        }
        else
        {
            printHelp();
            throw OdmOrthoPhotoException("Unrecognised argument '" + argument + "'");
        }
    }
    log_ << "\n";
}

void OdmOrthoPhoto::printHelp()
{
    log_.setIsPrintingInCout(true);

    log_ << "OpenDroneMapOrthoPhoto.exe\n\n";

    log_ << "Purpose\n";
    log_ << "Create an orthograpical photo from an oriented textured mesh.\n\n";

    log_ << "Usage:\n";
    log_ << "The program requires a path to an input OBJ mesh file and a resolution, as pixels/m. All other input parameters are optional.\n\n";

    log_ << "The following flags are available\n";
    log_ << "Call the program with flag \"-help\", or without parameters to print this message, or check any generated log file.\n";
    log_ << "Call the program with flag \"-verbose\", to print log messages in the standard output stream as well as in the log file.\n\n";

    log_ << "Parameters are specified as: \"-<argument name> <argument>\", (without <>), and the following parameters are configureable:n";
    log_ << "\"-inputFile <path>\" (mandatory)\n";
    log_ << "\"Input obj file that must contain a textured mesh.\n\n";

    log_ << "\"-inputGeoRefFile <path>\" (optional, if specified boundary points are assumed to be given as world coordinates. If not specified, the boundary points are assumed to be local coordinates)\n";
    log_ << "\"Input geograpical reference system file that describes the world position of the model's origin.\n\n";

    log_ << "\"-outputFile <path>\" (optional, default: ortho.jpg)\n";
    log_ << "\"Target file in which the orthophoto is saved.\n\n";

    log_ << "\"-outputCornerFile <path>\" (optional)\n";
    log_ << "\"Target text file for boundary corner points, written as \"xmin ymin xmax ymax\".\n\n";

    log_ << "\"-resolution <pixels/m>\" (mandatory)\n";
    log_ << "\"The number of pixels used per meter.\n\n";

    log_ << "\"-boundary <Point1x Point1y Point2x Point2y Point3x Point3y Point4x Point4y>\" (optional, if not specified the entire model will be rendered)\n";
    log_ << "\"Describes the area which should be covered in the ortho photo. The area will be a bounding box containing all four points. The points should be given in the same georeference system as the model.\n\n";

    log_ << "\"-boundaryMinMax <MinX MinY MaxX MaxY>\" (optional, if not specified the entire model will be rendered.)\n";
    log_ << "\"Describes the area which should be covered in the ortho photo. The area will be a bounding box with corners at MinX, MinY and MaxX, MaxY. The points should be given in the same georeference system as the model.\n\n";

    log_.setIsPrintingInCout(false);
}

void OdmOrthoPhoto::createOrthoPhoto()
{
    if(inputFile_.empty())
    {
        throw OdmOrthoPhotoException("Failed to create ortho photo, no texture mesh given.");
    }

    if(boundaryDefined_)
    {
        if(inputGeoRefFile_.empty())
        {
            // Points are assumed to be given in as local points.
            adjustBoundsForLocal();
        }
        else
        {
            // Points are assumed to be given in as world points.
            adjustBoundsForGeoRef();
        }
    }
    else if(!inputGeoRefFile_.empty())
    {
        // No boundary points specified, but georeference system file was given.
        log_ << "Warning:\n";
        log_ << "\tSpecified -inputGeoRefFile, but no boundary points. The georeference system will be ignored.\n";
    }

    log_ << "Reading mesh file...\n";
    // The textureds mesh.
    pcl::TextureMesh mesh;
    pcl::io::loadOBJFile(inputFile_, mesh);
    log_ << ".. mesh file read.\n\n";

    // Does the model have more than one material?
    multiMaterial_ = 1 < mesh.tex_materials.size();

    if(multiMaterial_)
    {
        // Need to check relationship between texture coordinates and faces.
        if(!isModelOk(mesh))
        {
            throw OdmOrthoPhotoException("Could not generate ortho photo: The given mesh has multiple textures, but the number of texture coordinates is NOT equal to 3 times the number of faces.");
        }
    }

    if(!boundaryDefined_)
    {
        // Determine boundary from model.
        adjustBoundsForEntireModel(mesh);
    }

    // The minimum and maximum boundary values.
    float xMax, xMin, yMax, yMin;
    xMin = std::min(std::min(boundaryPoint1_[0], boundaryPoint2_[0]), std::min(boundaryPoint3_[0], boundaryPoint4_[0]));
    xMax = std::max(std::max(boundaryPoint1_[0], boundaryPoint2_[0]), std::max(boundaryPoint3_[0], boundaryPoint4_[0]));
    yMin = std::min(std::min(boundaryPoint1_[1], boundaryPoint2_[1]), std::min(boundaryPoint3_[1], boundaryPoint4_[1]));
    yMax = std::max(std::max(boundaryPoint1_[1], boundaryPoint2_[1]), std::max(boundaryPoint3_[1], boundaryPoint4_[1]));

    log_ << "Ortho photo bounds x : " << xMin << " -> " << xMax << '\n';
    log_ << "Ortho photo bounds y : " << yMin << " -> " << yMax << '\n';

    // The size of the area.
    float xDiff = xMax - xMin;
    float yDiff = yMax - yMin;
    log_ << "Ortho photo area : " << xDiff*yDiff << "m2\n";

    // The resolution neccesary to fit the area with the given resolution.
    int rowRes = static_cast<int>(std::ceil(resolution_*yDiff));
    int colRes = static_cast<int>(std::ceil(resolution_*xDiff));
    log_ << "Ortho photo resolution, width x height : " << colRes << "x" << rowRes << '\n';

    // Check size of photo.
    if(0 >= rowRes*colRes)
    {
        if(0 >= rowRes)
        {
            log_ << "Warning: ortho photo has zero area, height = " << rowRes << ". Forcing height = 1.\n";
            rowRes = 1;
        }
        if(0 >= colRes)
        {
            log_ << "Warning: ortho photo has zero area, width = " << colRes << ". Forcing width = 1.\n";
            colRes = 1;
        }
        log_ << "New ortho photo resolution, width x height : " << colRes << "x" << rowRes << '\n';
    }

    // Init ortho photo
    photo_ = cv::Mat::zeros(rowRes, colRes, CV_8UC4) + cv::Scalar(255, 255, 255, 0);
    depth_ = cv::Mat::zeros(rowRes, colRes, CV_32F) - std::numeric_limits<float>::infinity();

    // Contains the vertices of the mesh.
    pcl::PointCloud<pcl::PointXYZ>::Ptr meshCloud (new pcl::PointCloud<pcl::PointXYZ>);
    pcl::fromPCLPointCloud2 (mesh.cloud, *meshCloud);

    // Creates a transformation which aligns the area for the ortho photo.
    Eigen::Transform<float, 3, Eigen::Affine> transform = getROITransform(xMin, -yMax);

    log_ << "Translating and scaling mesh...\n";

    // Move the mesh into position.
    pcl::transformPointCloud(*meshCloud, *meshCloud, transform);
    log_ << ".. mesh translated and scaled.\n\n";

    // Flatten texture coordiantes.
    std::vector<Eigen::Vector2f> uvs;
    for(size_t t = 0; t < mesh.tex_coordinates.size(); ++t)
    {
        uvs.insert(uvs.end(), mesh.tex_coordinates[t].begin(), mesh.tex_coordinates[t].end());
    }

    // The current material texture
    cv::Mat texture;

    // Used to keep track of the global face index.
    size_t faceOff = 0;

    log_ << "Rendering the ortho photo...\n";

    // Iterate over each part of the mesh (one per material).
    for(size_t t = 0; t < mesh.tex_materials.size(); ++t)
    {
        // The material of the current submesh.
        pcl::TexMaterial material = mesh.tex_materials[t];
        texture = cv::imread(material.tex_file);
        
        // Check for missing files.
        if(texture.empty())
        {
            log_ << "Material texture could not be read:\n";
            log_ << material.tex_file << '\n';
            log_ << "Could not be read as image, does the file exist?\n";
            continue; // Skip to next material.
        }

        // The faces of the current submesh.
        std::vector<pcl::Vertices> faces = mesh.tex_polygons[t];

        // Iterate over each face...
        for(size_t faceIndex = 0; faceIndex < faces.size(); ++faceIndex)
        {
            // The current polygon.
            pcl::Vertices polygon = faces[faceIndex];

            // ... and draw it into the ortho photo.
            drawTexturedTriangle(texture, polygon, meshCloud, uvs, faceIndex+faceOff);
        }
        faceOff += faces.size();
        log_ << "Material " << t << " rendered.\n";
    }
    log_ << "...ortho photo rendered\n";

    log_ << '\n';
    log_ << "Writing ortho photo to " << outputFile_ << "\n";
    cv::imwrite(outputFile_, photo_);

    if (!outputCornerFile_.empty())
    {
        log_ << "Writing corner coordinates to " << outputCornerFile_ << "\n";
        std::ofstream cornerStream(outputCornerFile_.c_str());
        if (!cornerStream.is_open())
        {
            throw OdmOrthoPhotoException("Failed opening output corner file " + outputCornerFile_ + ".");
        }
        cornerStream.setf(std::ios::scientific, std::ios::floatfield);
        cornerStream.precision(17);
        cornerStream << xMin << " " << yMin << " " << xMax << " " << yMax;
        cornerStream.close();
    }

    log_ << "Orthophoto generation done.\n";
}

void OdmOrthoPhoto::adjustBoundsForGeoRef()
{
    log_ << "Adjusting bounds for world coordinates\n";

    // A stream of the georef system.
    std::ifstream geoRefStream(inputGeoRefFile_.c_str());

    // The system name
    std::string system;
    // The east and north offsets
    int eastOffset, northOffset;

    // Parse file
    std::getline(geoRefStream, system);
    if(!(geoRefStream >> eastOffset))
    {
            throw OdmOrthoPhotoException("Could not extract geographical reference system from \n" + inputGeoRefFile_ + "\nCould not extract east offset.");
    }
    if(!(geoRefStream >> northOffset))
    {
            throw OdmOrthoPhotoException("Could not extract geographical reference system from \n" + inputGeoRefFile_ + "\nCould not extract north offset.");
    }

    log_ << "Georeference system:\n";
    log_ << system << "\n";
    log_ << "East offset: " << eastOffset << "\n";
    log_ << "North offset: " << northOffset << "\n";

    // Adjust boundary points.
    boundaryPoint1_[0] = static_cast<float>(worldPoint1_.eastInteger_  - eastOffset)  + worldPoint1_.eastFractional_;
    boundaryPoint1_[1] = static_cast<float>(worldPoint1_.northInteger_ - northOffset) + worldPoint1_.northFractional_;
    boundaryPoint2_[0] = static_cast<float>(worldPoint2_.eastInteger_  - eastOffset)  + worldPoint2_.eastFractional_;
    boundaryPoint2_[1] = static_cast<float>(worldPoint2_.northInteger_ - northOffset) + worldPoint2_.northFractional_;
    boundaryPoint3_[0] = static_cast<float>(worldPoint3_.eastInteger_  - eastOffset)  + worldPoint3_.eastFractional_;
    boundaryPoint3_[1] = static_cast<float>(worldPoint3_.northInteger_ - northOffset) + worldPoint3_.northFractional_;
    boundaryPoint4_[0] = static_cast<float>(worldPoint4_.eastInteger_  - eastOffset)  + worldPoint4_.eastFractional_;
    boundaryPoint4_[1] = static_cast<float>(worldPoint4_.northInteger_ - northOffset) + worldPoint4_.northFractional_;

    log_ << "Local boundary points:\n";
    log_ << "Point 1: " << boundaryPoint1_[0] << " " << boundaryPoint1_[1] << "\n";
    log_ << "Point 2: " << boundaryPoint2_[0] << " " << boundaryPoint2_[1] << "\n";
    log_ << "Point 3: " << boundaryPoint3_[0] << " " << boundaryPoint3_[1] << "\n";
    log_ << "Point 4: " << boundaryPoint4_[0] << " " << boundaryPoint4_[1] << "\n";
}

void OdmOrthoPhoto::adjustBoundsForLocal()
{
    log_ << "Adjusting bounds for local coordinates\n";

    // Set boundary points from world points.
    boundaryPoint1_[0] = static_cast<float>(worldPoint1_.eastInteger_ )  + worldPoint1_.eastFractional_;
    boundaryPoint1_[1] = static_cast<float>(worldPoint1_.northInteger_) + worldPoint1_.northFractional_;
    boundaryPoint2_[0] = static_cast<float>(worldPoint2_.eastInteger_ )  + worldPoint2_.eastFractional_;
    boundaryPoint2_[1] = static_cast<float>(worldPoint2_.northInteger_) + worldPoint2_.northFractional_;
    boundaryPoint3_[0] = static_cast<float>(worldPoint3_.eastInteger_ )  + worldPoint3_.eastFractional_;
    boundaryPoint3_[1] = static_cast<float>(worldPoint3_.northInteger_) + worldPoint3_.northFractional_;
    boundaryPoint4_[0] = static_cast<float>(worldPoint4_.eastInteger_ )  + worldPoint4_.eastFractional_;
    boundaryPoint4_[1] = static_cast<float>(worldPoint4_.northInteger_) + worldPoint4_.northFractional_;

    log_ << "Local boundary points:\n";
    log_ << "Point 1: " << boundaryPoint1_[0] << " " << boundaryPoint1_[1] << "\n";
    log_ << "Point 2: " << boundaryPoint2_[0] << " " << boundaryPoint2_[1] << "\n";
    log_ << "Point 3: " << boundaryPoint3_[0] << " " << boundaryPoint3_[1] << "\n";
    log_ << "Point 4: " << boundaryPoint4_[0] << " " << boundaryPoint4_[1] << "\n";
    log_ << "\n";
}

void OdmOrthoPhoto::adjustBoundsForEntireModel(const pcl::TextureMesh &mesh)
{
    log_ << "Set boundary to contain entire model.\n";

    // The boundary of the model.
    float xMin, xMax, yMin, yMax;

    xMin = std::numeric_limits<float>::infinity();
    xMax = -std::numeric_limits<float>::infinity();
    yMin = std::numeric_limits<float>::infinity();
    yMax = -std::numeric_limits<float>::infinity();

    // Contains the vertices of the mesh.
    pcl::PointCloud<pcl::PointXYZ>::Ptr meshCloud (new pcl::PointCloud<pcl::PointXYZ>);
    pcl::fromPCLPointCloud2 (mesh.cloud, *meshCloud);

    for(size_t t = 0; t < mesh.tex_materials.size(); ++t)
    {
        // The faces of the current submesh.
        std::vector<pcl::Vertices> faces = mesh.tex_polygons[t];

        // Iterate over each face...
        for(size_t faceIndex = 0; faceIndex < faces.size(); ++faceIndex)
        {
            // The current polygon.
            pcl::Vertices polygon = faces[faceIndex];

            // The index to the vertices of the polygon.
            size_t v1i = polygon.vertices[0];
            size_t v2i = polygon.vertices[1];
            size_t v3i = polygon.vertices[2];

            // The polygon's points.
            pcl::PointXYZ v1 = meshCloud->points[v1i];
            pcl::PointXYZ v2 = meshCloud->points[v2i];
            pcl::PointXYZ v3 = meshCloud->points[v3i];

            xMin = std::min(std::min(xMin, v1.x), std::min(v2.x, v3.x));
            xMax = std::max(std::max(xMax, v1.x), std::max(v2.x, v3.x));
            yMin = std::min(std::min(yMin, v1.y), std::min(v2.y, v3.y));
            yMax = std::max(std::max(yMax, v1.y), std::max(v2.y, v3.y));
        }
    }

    // Create dummy boundary points.
    boundaryPoint1_[0] = xMin; boundaryPoint1_[1] = yMin;
    boundaryPoint2_[0] = xMin; boundaryPoint2_[1] = yMax;
    boundaryPoint3_[0] = xMax; boundaryPoint3_[1] = yMax;
    boundaryPoint4_[0] = xMax; boundaryPoint4_[1] = yMin;

    log_ << "Local boundary points:\n";
    log_ << "Point 1: " << boundaryPoint1_[0] << " " << boundaryPoint1_[1] << "\n";
    log_ << "Point 2: " << boundaryPoint2_[0] << " " << boundaryPoint2_[1] << "\n";
    log_ << "Point 3: " << boundaryPoint3_[0] << " " << boundaryPoint3_[1] << "\n";
    log_ << "Point 4: " << boundaryPoint4_[0] << " " << boundaryPoint4_[1] << "\n";
    log_ << "\n";
}

Eigen::Transform<float, 3, Eigen::Affine> OdmOrthoPhoto::getROITransform(float xMin, float yMin) const
{
    // The tranform used to move the chosen area into the ortho photo.
    Eigen::Transform<float, 3, Eigen::Affine> transform;

    transform(0, 0) = resolution_;     // x Scaling.
    transform(1, 0) = 0.0f;
    transform(2, 0) = 0.0f;
    transform(3, 0) = 0.0f;

    transform(0, 1) = 0.0f;
    transform(1, 1) = -resolution_;     // y Scaling, mirrored for easier rendering.
    transform(2, 1) = 0.0f;
    transform(3, 1) = 0.0f;

    transform(0, 2) = 0.0f;
    transform(1, 2) = 0.0f;
    transform(2, 2) = 1.0f;
    transform(3, 2) = 0.0f;

    transform(0, 3) = -xMin*resolution_;    // x Translation
    transform(1, 3) = -yMin*resolution_;    // y Translation
    transform(2, 3) = 0.0f;
    transform(3, 3) = 1.0f;

    return transform;
}

void OdmOrthoPhoto::drawTexturedTriangle(const cv::Mat &texture, const pcl::Vertices &polygon, const pcl::PointCloud<pcl::PointXYZ>::Ptr &meshCloud, const std::vector<Eigen::Vector2f> &uvs, size_t faceIndex)
{
    // The index to the vertices of the polygon.
    size_t v1i = polygon.vertices[0];
    size_t v2i = polygon.vertices[1];
    size_t v3i = polygon.vertices[2];

    // The polygon's points.
    pcl::PointXYZ v1 = meshCloud->points[v1i];
    pcl::PointXYZ v2 = meshCloud->points[v2i];
    pcl::PointXYZ v3 = meshCloud->points[v3i];

    if(isSliverPolygon(v1, v2, v3))
    {
        log_ << "Warning: Sliver polygon found at face index " << faceIndex << '\n';
        return;
    }

    // The face data. Position v*{x,y,z}. Texture coordinate v*{u,v}. * is the vertex number in the polygon.
    float v1x, v1y, v1z, v1u, v1v;
    float v2x, v2y, v2z, v2u, v2v;
    float v3x, v3y, v3z, v3u, v3v;

    // Barycentric coordinates of the currently rendered point.
    float l1, l2, l3;

    // The size of the photo, as float.
    float fRows, fCols;
    fRows = static_cast<float>(texture.rows);
    fCols = static_cast<float>(texture.cols);

    // Get vertex position.
    v1x = v1.x; v1y = v1.y; v1z = v1.z;
    v2x = v2.x; v2y = v2.y; v2z = v2.z;
    v3x = v3.x; v3y = v3.y; v3z = v3.z;

    // Get texture coorinates. (Special cases for PCL when using multiple materials vs one material)
    if(multiMaterial_)
    {
        v1u = uvs[3*faceIndex][0]; v1v = uvs[3*faceIndex][1];
        v2u = uvs[3*faceIndex+1][0]; v2v = uvs[3*faceIndex+1][1];
        v3u = uvs[3*faceIndex+2][0]; v3v = uvs[3*faceIndex+2][1];
    }
    else
    {
        v1u = uvs[v1i][0]; v1v = uvs[v1i][1];
        v2u = uvs[v2i][0]; v2v = uvs[v2i][1];
        v3u = uvs[v3i][0]; v3v = uvs[v3i][1];
    }

    // Check bounding box overlap.
    int xMin = static_cast<int>(std::min(std::min(v1x, v2x), v3x));
    if(xMin > photo_.cols)
    {
        return; // Completly outside to the right.
    }
    int xMax = static_cast<int>(std::max(std::max(v1x, v2x), v3x));
    if(xMax < 0)
    {
        return; // Completly outside to the left.
    }
    int yMin = static_cast<int>(std::min(std::min(v1y, v2y), v3y));
    if(yMin > photo_.rows)
    {
        return; // Completly outside to the top.
    }
    int yMax = static_cast<int>(std::max(std::max(v1y, v2y), v3y));
    if(yMax < 0)
    {
        return; // Completly outside to the bottom.
    }

    // Top point row and column positions
    float topR, topC;
    // Middle point row and column positions
    float midR, midC;
    // Bottom point row and column positions
    float botR, botC;

    // Find top, middle and bottom points.
    if(v1y < v2y)
    {
        if(v1y < v3y)
        {
            if(v2y < v3y)
            {
                // 1 -> 2 -> 3
                topR = v1y; topC = v1x;
                midR = v2y; midC = v2x;
                botR = v3y; botC = v3x;
            }
            else
            {
                // 1 -> 3 -> 2
                topR = v1y; topC = v1x;
                midR = v3y; midC = v3x;
                botR = v2y; botC = v2x;
            }
        }
        else
        {
            // 3 -> 1 -> 2
            topR = v3y; topC = v3x;
            midR = v1y; midC = v1x;
            botR = v2y; botC = v2x;
        }        
    }
    else // v2y <= v1y
    {
        if(v2y < v3y)
        {
            if(v1y < v3y)
            {
                // 2 -> 1 -> 3
                topR = v2y; topC = v2x;
                midR = v1y; midC = v1x;
                botR = v3y; botC = v3x;
            }
            else
            {
                // 2 -> 3 -> 1
                topR = v2y; topC = v2x;
                midR = v3y; midC = v3x;
                botR = v1y; botC = v1x;
            }
        }
        else
        {
            // 3 -> 2 -> 1
            topR = v3y; topC = v3x;
            midR = v2y; midC = v2x;
            botR = v1y; botC = v1x;
        }
    }

    // General appreviations:
    // ---------------------
    // tm : Top(to)Middle.
    // mb : Middle(to)Bottom.
    // tb : Top(to)Bottom.
    // c  : column.
    // r  : row.
    // dr : DeltaRow, step value per row.

    // The step along column for every step along r. Top to middle.
    float ctmdr;
    // The step along column for every step along r. Top to bottom.
    float ctbdr;
    // The step along column for every step along r. Middle to bottom.
    float cmbdr;

    ctbdr = (botC-topC)/(botR-topR);

    // The current column position, from top to middle.
    float ctm = topC;
    // The current column position, from top to bottom.
    float ctb = topC;

    // Check for vertical line between middle and top.
    if(FLT_EPSILON < midR-topR)
    {
        ctmdr = (midC-topC)/(midR-topR);

        // The first pixel row for the bottom part of the triangle.
        int rqStart = std::max(static_cast<int>(std::floor(topR+0.5f)), 0);
        // The last pixel row for the top part of the triangle.
        int rqEnd = std::min(static_cast<int>(std::floor(midR+0.5f)), photo_.rows);

        // Travers along row from top to middle.
        for(int rq = rqStart; rq < rqEnd; ++rq)
        {
            // Set the current column positions.
            ctm = topC + ctmdr*(static_cast<float>(rq)+0.5f-topR);
            ctb = topC + ctbdr*(static_cast<float>(rq)+0.5f-topR);

            // The first pixel column for the current row.
            int cqStart = std::max(static_cast<int>(std::floor(0.5f+std::min(ctm, ctb))), 0);
            // The last pixel column for the current row.
            int cqEnd = std::min(static_cast<int>(std::floor(0.5f+std::max(ctm, ctb))), photo_.cols);

            for(int cq = cqStart; cq < cqEnd; ++cq)
            {
                // Get barycentric coordinates for the current point.
                getBarycentricCoordiantes(v1, v2, v3, static_cast<float>(cq)+0.5f, static_cast<float>(rq)+0.5f, l1, l2, l3);
                
                if(0.f > l1 || 0.f > l2 || 0.f > l3)
                {
                    //continue;
                }
                
                // The z value for the point.
                float z = v1z*l1+v2z*l2+v3z*l3;

                // Check depth
                float depthValue = depth_.at<float>(rq, cq);
                if(z < depthValue)
                {
                    // Current is behind another, don't draw.
                    continue;
                }

                // The uv values of the point.
                float u, v;
                u = v1u*l1+v2u*l2+v3u*l3;
                v = v1v*l1+v2v*l2+v3v*l3;
                
                renderPixel(rq, cq, u*fCols, (1.0f-v)*fRows, texture);
                
                // Update depth buffer.
                depth_.at<float>(rq, cq) = z;
            }
        }
    }

    if(FLT_EPSILON < botR-midR)
    {
        cmbdr = (botC-midC)/(botR-midR);

        // The current column position, from middle to bottom.
        float cmb = midC;

        // The first pixel row for the bottom part of the triangle.
        int rqStart = std::max(static_cast<int>(std::floor(midR+0.5f)), 0);
        // The last pixel row for the bottom part of the triangle.
        int rqEnd = std::min(static_cast<int>(std::floor(botR+0.5f)), photo_.rows);

        // Travers along row from middle to bottom.
        for(int rq = rqStart; rq < rqEnd; ++rq)
        {
            // Set the current column positions.
            ctb = topC + ctbdr*(static_cast<float>(rq)+0.5f-topR);
            cmb = midC + cmbdr*(static_cast<float>(rq)+0.5f-midR);

            // The first pixel column for the current row.
            int cqStart = std::max(static_cast<int>(std::floor(0.5f+std::min(cmb, ctb))), 0);
            // The last pixel column for the current row.
            int cqEnd = std::min(static_cast<int>(std::floor(0.5f+std::max(cmb, ctb))), photo_.cols);

            for(int cq = cqStart; cq < cqEnd; ++cq)
            {
                // Get barycentric coordinates for the current point.
                getBarycentricCoordiantes(v1, v2, v3, static_cast<float>(cq)+0.5f, static_cast<float>(rq)+0.5f, l1, l2, l3);
                
                if(0.f > l1 || 0.f > l2 || 0.f > l3)
                {
                    //continue;
                }

                // The z value for the point.
                float z = v1z*l1+v2z*l2+v3z*l3;

                // Check depth
                float depthValue = depth_.at<float>(rq, cq);
                if(z < depthValue)
                {
                    // Current is behind another, don't draw.
                    continue;
                }

                // The uv values of the point.
                float u, v;
                u = v1u*l1+v2u*l2+v3u*l3;
                v = v1v*l1+v2v*l2+v3v*l3;

                renderPixel(rq, cq, u*fCols, (1.0f-v)*fRows, texture);

                // Update depth buffer.
                depth_.at<float>(rq, cq) = z;
            }
        }
    }
}

void OdmOrthoPhoto::renderPixel(int row, int col, float s, float t, const cv::Mat &texture)
{
    // The colors of the texture pixels. tl : top left, tr : top right, bl : bottom left, br : bottom right.
    cv::Vec3b tl, tr, bl, br;
    
    // The offset of the texture coordinate from its pixel positions.
    float leftF, topF;
    // The position of the top left pixel.
    int left, top;
    // The distance to the left and right pixel from the texture coordinate.
    float dl, dt;
    // The distance to the top and bottom pixel from the texture coordinate.
    float dr, db;
    
    dl = modff(s, &leftF);
    dr = 1.0f - dl;
    dt = modff(t, &topF);
    db = 1.0f - dt;
    
    left = static_cast<int>(leftF);
    top = static_cast<int>(topF);
    
    tl = texture.at<cv::Vec3b>(top, left);
    tr = texture.at<cv::Vec3b>(top, left+1);
    bl = texture.at<cv::Vec3b>(top+1, left);
    br = texture.at<cv::Vec3b>(top+1, left+1);
    
    // The interpolated color values.
    float r = 0.0f, g = 0.0f, b = 0.0f;
    
    // Red
    r += static_cast<float>(tl[2]) * dr * db;
    r += static_cast<float>(tr[2]) * dl * db;
    r += static_cast<float>(bl[2]) * dr * dt;
    r += static_cast<float>(br[2]) * dl * dt;
    
    // Green
    g += static_cast<float>(tl[1]) * dr * db;
    g += static_cast<float>(tr[1]) * dl * db;
    g += static_cast<float>(bl[1]) * dr * dt;
    g += static_cast<float>(br[1]) * dl * dt;
    
    // Blue
    b += static_cast<float>(tl[0]) * dr * db;
    b += static_cast<float>(tr[0]) * dl * db;
    b += static_cast<float>(bl[0]) * dr * dt;
    b += static_cast<float>(br[0]) * dl * dt;
    
    photo_.at<cv::Vec4b>(row,col) = cv::Vec4b(static_cast<unsigned char>(b), static_cast<unsigned char>(g), static_cast<unsigned char>(r), 255);
}

void OdmOrthoPhoto::getBarycentricCoordiantes(pcl::PointXYZ v1, pcl::PointXYZ v2, pcl::PointXYZ v3, float x, float y, float &l1, float &l2, float &l3) const
{
    // Diff along y.
    float y2y3 = v2.y-v3.y;
    float y1y3 = v1.y-v3.y;
    float y3y1 = v3.y-v1.y;
    float yy3  =  y  -v3.y;
    
    // Diff along x.
    float x3x2 = v3.x-v2.x;
    float x1x3 = v1.x-v3.x;
    float xx3  =  x  -v3.x;
    
    // Normalization factor.
    float norm = (y2y3*x1x3 + x3x2*y1y3);
    
    l1 = (y2y3*(xx3) + x3x2*(yy3)) / norm;
    l2 = (y3y1*(xx3) + x1x3*(yy3)) / norm;
    l3 = 1 - l1 - l2;
}

bool OdmOrthoPhoto::isSliverPolygon(pcl::PointXYZ v1, pcl::PointXYZ v2, pcl::PointXYZ v3) const
{
    // Calculations are made using doubles, to minize rounding errors.
    Eigen::Vector3d a = Eigen::Vector3d(static_cast<double>(v1.x), static_cast<double>(v1.y), static_cast<double>(v1.z));
    Eigen::Vector3d b = Eigen::Vector3d(static_cast<double>(v2.x), static_cast<double>(v2.y), static_cast<double>(v2.z));
    Eigen::Vector3d c = Eigen::Vector3d(static_cast<double>(v3.x), static_cast<double>(v3.y), static_cast<double>(v3.z));
    Eigen::Vector3d dummyVec = (a-b).cross(c-b);

    // Area smaller than, or equal to, floating-point epsilon.
    return std::numeric_limits<float>::epsilon() >= static_cast<float>(std::sqrt(dummyVec.dot(dummyVec))/2.0);
}

bool OdmOrthoPhoto::isModelOk(const pcl::TextureMesh &mesh)
{
    // The number of texture coordinates in the model.
    size_t nTextureCoordinates = 0;
    // The number of faces in the model.
    size_t nFaces = 0;
    
    for(size_t t = 0; t < mesh.tex_coordinates.size(); ++t)
    {
        nTextureCoordinates += mesh.tex_coordinates[t].size();
    }
    for(size_t t = 0; t < mesh.tex_polygons.size(); ++t)
    {
        nFaces += mesh.tex_polygons[t].size();
    }
    
    log_ << "Number of faces in the model " << nFaces << '\n';
    
    return 3*nFaces == nTextureCoordinates;
}

One of many scripts required to run OpenDroneMap on Linux via Command Line. See more at GitHub.

I use Pix4D

Other options include

  • OpenDroneMapper
  • Agisoft
  • Drone Deploy

Accuracy

Error

Relative Accuracy

(need ground control points)

Absolute Accuracy

 It is the accuracy that is defined by the difference between the location of features on a map / reconstructed model / orthomosaic and their true position on the Earth.

UAVs and Maps

By Britta Ricker

UAVs and Maps

Utilizing low-cost unmanned vehicle (UAV) to build orthophotos and Digital Surface Models Speaker: Britta Ricker, PhD When: Weds. Dec. 16, 2015 Noon – 1pm Where: USGS Water Science Center Office – Tacoma Columbia Conference room 934 Broadway, Suite 300 Tacoma, WA 98402 In this presentation, I will briefly contextualize this evolution by presenting how photogrammetry is reaching a confluence with structure for motion (SfM) software and why this is important. I will introduce methods of aerial imagery collection through the use of a low-cost and popular UAV systems. I will then focus on how to process the imagery to generate orthophotos and digital surface models (DSM) through the use of SfM software. I will conclude by presenting additional considerations including legal regulations, good flying practice, accuracy and precision and future research.

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