C#获取全景图片中xmp的陀螺仪数据

现在的全景相机，厂商会写入一些全景图片的拍摄参数，一般会遵从google出的标准。比如理光相机，重要的信息都存在了Exif和Photo Sphere XMP里了（这些链接都是google的，请科学上网），这对后期用于进一步的图形处理来说非常重要。

这里我需要的是全景相机的陀螺仪数据PoseHeadingDegrees，PosePitchDegrees，PoseRollDegrees，这样即使用户歪着拍摄的全景照片，后期依然能正确方向显示出来，避免用户看着头晕。

这里我用了些非主流的方式来获取，简单粗暴而又不失”优雅”，直接上代码。

using System;
using System.IO;
using System.Text;
using System.Xml;

public class PanoXmpReader
{
    public int FullPanoWidthPixels;
    public int FullPanoHeightPixels;
    public float PoseHeadingDegrees;
    public float PosePitchDegrees;
    public float PoseRollDegrees;

    public static PanoXmpReader Read(byte[] xmpBytes)
    {
        var xmlDocument = ExtractXmp(xmpBytes);

        PanoXmpReader panoXmp = new PanoXmpReader();
        panoXmp.FullPanoWidthPixels = GetIntValue(xmlDocument, "GPano:FullPanoWidthPixels");
        panoXmp.FullPanoHeightPixels = GetIntValue(xmlDocument, "GPano:FullPanoHeightPixels");
        panoXmp.PoseHeadingDegrees = GetFloatValue(xmlDocument, "GPano:PoseHeadingDegrees");
        panoXmp.PosePitchDegrees = GetFloatValue(xmlDocument, "GPano:PosePitchDegrees");
        panoXmp.PoseRollDegrees = GetFloatValue(xmlDocument, "GPano:PoseRollDegrees");

        return panoXmp;
    }

    public static PanoXmpReader Read(string imagePath)
    {
        PanoXmpReader panoXmp = new PanoXmpReader();
        FileStream stream = null;
        int xmpBytesLength = 1024 * 100;

        try
        {
            stream = File.OpenRead(imagePath);

            byte[] xmpBytes = new byte[xmpBytesLength];

            stream.Read(xmpBytes, 0, xmpBytesLength);

            panoXmp = Read(xmpBytes);
        }
        catch (Exception)
        {
            // Nothing
        }
        finally
        {
            if (stream != null)
            {
                stream.Close();
            }
        }

        return panoXmp;
    }

    private static int GetIntValue(XmlDocument xmlDocument, string tagName, int defaultValue = 0)
    {
        int value = defaultValue;

        var node = xmlDocument.GetElementsByTagName(tagName)[0];

        if (node != null)
        {
            int result;

            if (int.TryParse(node.InnerText, out result))
            {
                value = result;
            }
        }

        return value;
    }

    private static float GetFloatValue(XmlDocument xmlDocument, string tagName, float defaultValue = 0)
    {
        float value = defaultValue;

        var node = xmlDocument.GetElementsByTagName(tagName)[0];

        if (node != null)
        {
            float result;

            if (float.TryParse(node.InnerText, out result))
            {
                value = result;
            }
        }

        return value;
    }

    private static XmlDocument ExtractXmp(byte[] xmpBytes)
    {
        var xmpString = Encoding.UTF8.GetString(xmpBytes);
        var start = xmpString.IndexOf("<x:xmpmeta");
        var end = xmpString.IndexOf("</x:xmpmeta>") + 12;

        if (start == -1 || end == -1)
        {
            return null;
        }

        var metaData = xmpString.Substring(start, end - start);
        var xmlDocument = new XmlDocument();
        xmlDocument.LoadXml(metaData);

        return xmlDocument;
    }
}

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using System;

using System.IO;

using System.Text;

using System.Xml;

public class PanoXmpReader

{

public int FullPanoWidthPixels;

public int FullPanoHeightPixels;

public float PoseHeadingDegrees;

public float PosePitchDegrees;

public float PoseRollDegrees;

public static PanoXmpReader Read(byte[] xmpBytes)

{

var xmlDocument = ExtractXmp(xmpBytes);

PanoXmpReader panoXmp = new PanoXmpReader();

panoXmp.FullPanoWidthPixels = GetIntValue(xmlDocument, "GPano:FullPanoWidthPixels");

panoXmp.FullPanoHeightPixels = GetIntValue(xmlDocument, "GPano:FullPanoHeightPixels");

panoXmp.PoseHeadingDegrees = GetFloatValue(xmlDocument, "GPano:PoseHeadingDegrees");

panoXmp.PosePitchDegrees = GetFloatValue(xmlDocument, "GPano:PosePitchDegrees");

panoXmp.PoseRollDegrees = GetFloatValue(xmlDocument, "GPano:PoseRollDegrees");

return panoXmp;

}

public static PanoXmpReader Read(string imagePath)

{

PanoXmpReader panoXmp = new PanoXmpReader();

FileStream stream = null;

int xmpBytesLength = 1024 * 100;

try

{

stream = File.OpenRead(imagePath);

byte[] xmpBytes = new byte[xmpBytesLength];

stream.Read(xmpBytes, 0, xmpBytesLength);

panoXmp = Read(xmpBytes);

}

catch (Exception)

{

// Nothing

}

finally

{

if (stream != null)

{

stream.Close();

}

return panoXmp;

}

private static int GetIntValue(XmlDocument xmlDocument, string tagName, int defaultValue = 0)

{

int value = defaultValue;

var node = xmlDocument.GetElementsByTagName(tagName)[0];

if (node != null)

{

int result;

if (int.TryParse(node.InnerText, out result))

{

value = result;

}

return value;

}

private static float GetFloatValue(XmlDocument xmlDocument, string tagName, float defaultValue = 0)

{

float value = defaultValue;

var node = xmlDocument.GetElementsByTagName(tagName)[0];

if (node != null)

{

float result;

if (float.TryParse(node.InnerText, out result))

{

value = result;

}

return value;

}

private static XmlDocument ExtractXmp(byte[] xmpBytes)

{

var xmpString = Encoding.UTF8.GetString(xmpBytes);

var start = xmpString.IndexOf("<x:xmpmeta");

var end = xmpString.IndexOf("</x:xmpmeta>") + 12;

if (start == -1 || end == -1)

{

return null;

}

var metaData = xmpString.Substring(start, end - start);

var xmlDocument = new XmlDocument();

xmlDocument.LoadXml(metaData);

return xmlDocument;

}

测试：我读取的是理光景达拍摄的5k JPEG图片，用ExtractXmp获取到的xml文件是下面这样的，用时18ms，凑活着用吧。

<?xml version="1.0" encoding="utf-8"?>

<x:xmpmeta xmlns:x="adobe:ns:meta/" xmptk="RICOH THETA S Ver1.82">
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <rdf:Description xmlns:GPano="http://ns.google.com/photos/1.0/panorama/" rdf:about="">
      <GPano:ProjectionType>equirectangular</GPano:ProjectionType>
      <GPano:UsePanoramaViewer>True</GPano:UsePanoramaViewer>
      <GPano:CroppedAreaImageWidthPixels>5376</GPano:CroppedAreaImageWidthPixels>
      <GPano:CroppedAreaImageHeightPixels>2688</GPano:CroppedAreaImageHeightPixels>
      <GPano:FullPanoWidthPixels>5376</GPano:FullPanoWidthPixels>
      <GPano:FullPanoHeightPixels>2688</GPano:FullPanoHeightPixels>
      <GPano:CroppedAreaLeftPixels>0</GPano:CroppedAreaLeftPixels>
      <GPano:CroppedAreaTopPixels>0</GPano:CroppedAreaTopPixels>
      <GPano:PoseHeadingDegrees>67.5</GPano:PoseHeadingDegrees>
      <GPano:PosePitchDegrees>1.2</GPano:PosePitchDegrees>
      <GPano:PoseRollDegrees>-1.0</GPano:PoseRollDegrees>
    </rdf:Description>
  </rdf:RDF>
</x:xmpmeta>

<?xml version="1.0" encoding="utf-8"?>

<x:xmpmeta xmlns:x="adobe:ns:meta/" xmptk="RICOH THETA S Ver1.82">

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">

<rdf:Description xmlns:GPano="http://ns.google.com/photos/1.0/panorama/" rdf:about="">

<GPano:ProjectionType>equirectangular</GPano:ProjectionType>

<GPano:UsePanoramaViewer>True</GPano:UsePanoramaViewer>

<GPano:CroppedAreaImageWidthPixels>5376</GPano:CroppedAreaImageWidthPixels>

<GPano:CroppedAreaImageHeightPixels>2688</GPano:CroppedAreaImageHeightPixels>

<GPano:FullPanoWidthPixels>5376</GPano:FullPanoWidthPixels>

<GPano:FullPanoHeightPixels>2688</GPano:FullPanoHeightPixels>

<GPano:CroppedAreaLeftPixels>0</GPano:CroppedAreaLeftPixels>

<GPano:CroppedAreaTopPixels>0</GPano:CroppedAreaTopPixels>

<GPano:PoseHeadingDegrees>67.5</GPano:PoseHeadingDegrees>

<GPano:PosePitchDegrees>1.2</GPano:PosePitchDegrees>

<GPano:PoseRollDegrees>-1.0</GPano:PoseRollDegrees>

</rdf:Description>

</rdf:RDF>

</x:xmpmeta>

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