使用二进制数据点生成 XML VTK 文件

Question

我要生成二进制 vtk 文件。

我写了一个代码，可以先生成正确的ascii vtk文件，然后对其进行一些修改，让它可以生成正确的二进制vtk文件。

我在将第一个 acsii 转换为二进制时遇到了问题，请参阅以下代码中的 if 开关。

#include <fstream>
int main()
{
    std::ofstream fout;
    bool is_binary = true;
    fout.open("new.vtu");
    fout << "<?xml version=\"1.0\"?>\n";
    fout << "<VTKFile type=\"UnstructuredGrid\" version=\"0.1\" byte_order=\"LittleEndian\" compressor=\"vtkZLibDataCompressor\">\n";
    fout << "<UnstructuredGrid>\n";
    fout << "<Piece NumberOfPoints=\"4\" NumberOfCells=\"2\">\n";
    fout << "<PointData Scalars=\"\" Vectors=\"\">\n";

    if (is_binary)
    {
        fout << "<DataArray type=\"Float64\" Name=\"solution\" NumberOfComponents=\"3\" format=\"binary\">\n";
        double x[] = {56.25, 6.25, 0, 100, 6.25, 0, 56.25, 0, 0, 100, 0, 0};
        for (int i = 0; i < 12; i++)
        {
            double value = x[i];
            fout.write((char *)(&value), sizeof(double));
        }
        fout << "\n";
    }
    else
    {
        fout << "<DataArray type=\"Float64\" Name=\"solution\" NumberOfComponents=\"3\" format=\"ascii\">\n";
        fout << "56.25 6.25 0\n";
        fout << "100 6.25 0\n";
        fout << "56.25 0 0\n";
        fout << "100 0 0\n";
    }

    fout << "</DataArray>\n";
    fout << "</PointData>\n";
    fout << "<Points>\n";
    fout << "<DataArray type=\"Float64\" NumberOfComponents=\"3\" format=\"ascii\">\n";
    fout << "7.5 2.5 0\n";
    fout << "10 2.5 0\n";
    fout << "7.5 0 0\n";
    fout << "10 0 0\n";
    fout << "</DataArray>\n";
    fout << "</Points>\n";
    fout << "<Cells>\n";
    fout << "<DataArray type=\"Int32\" Name = \"connectivity\" format=\"ascii\">\n";
    fout << "0 2 1\n";
    fout << "1 2 3\n";
    fout << "</DataArray>\n";
    fout << "<DataArray type=\"Int32\" Name = \"offsets\" format=\"ascii\">\n";
    fout << "3\n";
    fout << "6\n";
    fout << "</DataArray>\n";
    fout << "<DataArray type=\"Int8\" Name = \"types\" format=\"ascii\">\n";
    fout << "5\n";
    fout << "5\n";
    fout << "5\n";
    fout << "5\n";
    fout << "</DataArray>\n";
    fout << "</Cells>\n";
    fout << "</Piece>\n";
    fout << "</UnstructuredGrid>\n";
    fout << "</VTKFile>\n";
    fout.close();
    return 0;
}

如果is_binary = false，代码可以生成正确的vtk文件，但是如果is_binary = true，代码不能生成正确的vtk文件。

如果我用paraview 打开 vtk 文件，它会抱怨：

Error parsing the XMKL in stream at line 7, column 0, bute index 311: not well-formed(invalid token)

Visit也打不开我的文件。

代码是用g++ main.cpp编译的，我的机器是little endian。

我已经看过很多话题了

• Error writing binary VTK files
• Write vtk file in binary format
• How to write ASCII and BINARY data to the same file at the same time

谁能帮帮我？但我仍然无法弄清楚我做错了什么。

感谢您的宝贵时间。

追加

感谢 Botje 先生提出应该使用 base64 编码的建议。

现在我已经使用base64编码了，但是bug还是存在的。

base64.h 复制自 https://github.com/superwills/NibbleAndAHalf/blob/master/NibbleAndAHalf/base64.h

#include <fstream>
#include <iostream>
#include "base64.h"
int main()
{
    std::ofstream fout;
    bool is_binary = true;
    fout.open("new.vtu",  std::ios::binary);
    fout << "<?xml version=\"1.0\"?>\n";
    fout << "<VTKFile type=\"UnstructuredGrid\" version=\"0.1\" byte_order=\"LittleEndian\" compressor=\"vtkZLibDataCompressor\">\n";
    fout << "<UnstructuredGrid>\n";
    fout << "<Piece NumberOfPoints=\"4\" NumberOfCells=\"2\">\n";
    fout << "<PointData Scalars=\"\" Vectors=\"\">\n";

    if (is_binary)
    {
        fout << "<DataArray type=\"Float64\" Name=\"solution\" NumberOfComponents=\"3\" format=\"binary\">\n";
        double x[] = {56.25, 6.25, 0, 100, 6.25, 0, 56.25, 0, 0, 100, 0, 0};
        int result_size;
        char *encoding = base64((char *)x, sizeof(double) * 12, &result_size);
        std::cout << result_size << std::endl;
        fout.write(encoding, result_size);
        free(encoding);
    }
    else
    {
        fout << "<DataArray type=\"Float64\" Name=\"solution\" NumberOfComponents=\"3\" format=\"ascii\">\n";
        fout << "56.25 6.25 0\n";
        fout << "100 6.25 0\n";
        fout << "56.25 0 0\n";
        fout << "100 0 0\n";
    }

    fout << "</DataArray>\n";
    fout << "</PointData>\n";
    fout << "<Points>\n";
    fout << "<DataArray type=\"Float64\" NumberOfComponents=\"3\" format=\"ascii\">\n";
    fout << "7.5 2.5 0\n";
    fout << "10 2.5 0\n";
    fout << "7.5 0 0\n";
    fout << "10 0 0\n";
    fout << "</DataArray>\n";
    fout << "</Points>\n";
    fout << "<Cells>\n";
    fout << "<DataArray type=\"Int32\" Name = \"connectivity\" format=\"ascii\">\n";
    fout << "0 2 1\n";
    fout << "1 2 3\n";
    fout << "</DataArray>\n";
    fout << "<DataArray type=\"Int32\" Name = \"offsets\" format=\"ascii\">\n";
    fout << "3\n";
    fout << "6\n";
    fout << "</DataArray>\n";
    fout << "<DataArray type=\"Int8\" Name = \"types\" format=\"ascii\">\n";
    fout << "5\n";
    fout << "5\n";
    fout << "5\n";
    fout << "5\n";
    fout << "</DataArray>\n";
    fout << "</Cells>\n";
    fout << "</Piece>\n";
    fout << "</UnstructuredGrid>\n";
    fout << "</VTKFile>\n";
    fout.close();
    return 0;
}

Answer 1

您不能在 XML 文件中转储二进制垃圾并期望它能够正常工作！

在 vtk file format 上的快速 Google 搜索告诉我，您需要先将您的浮点数 base64 编码为 XML 安全字符，以用于 format="binary"。

您可以在 Internet 上找到许多（仅标头）base64 库，我确信 StackOverflow 有几个现成的实现。