[gdal-dev] Extract CGM from a NITF file

[Livneh Yehiyam]

Hi
You can use the GDAL unescape function like this:

/// <summary>
        /// Remove "backslash quotable" escape characters from the string and convert it to byte array.
        /// </summary>
        public static byte[] RemoveEscapeCharacters(this string value)
        {
            if(String.IsNullOrEmpty(value))
            {
                return new byte[0];
            }
            int length = value.Length;
            IntPtr escapedString = CPLUnescapeString(value, ref length, 0);
            byte[] escapedBytes = new byte[length];
            Marshal.Copy(escapedString, escapedBytes, 0, length);
            VSIFree(escapedString);
            return escapedBytes;
        }

        [DllImport("gdal18.dll", EntryPoint = "CPLUnescapeString", CallingConvention = CallingConvention.Cdecl)]
        private static extern IntPtr CPLUnescapeString(string input, ref int length, int scheme);

        [DllImport("gdal18.dll", EntryPoint = "VSIFree", CallingConvention = CallingConvention.Cdecl)]
        private static extern void VSIFree(IntPtr input);


Yehiyam


From: gdal-dev-bounces at lists.osgeo.org [mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of xavier lhomme
Sent: Wednesday, June 19, 2013 11:50 PM
To: gdal-dev
Subject: [gdal-dev] Extract CGM from a NITF file

Hi

  I'm trying to extract CGM files from a NITF but the CGM are corrupt.

  First I Unescape the CGM Data and I obtain something like
   "\0,\vCreated CGM \"\0 f\0 ÿÿ\0 ...
  Then write the text file.

  I compared this string with a CGM obtained from NITRO NITF (nitro_extract_cgm.exe).
  The new CGM file start with
    "\0,\vCreated CGM \"\0 f\0 ��\0
 I succeed to read this CGM file with a CGM viewer.

One of the difference come from caracter like ÿ (from GDAL) � from NITRO

Then It's probably something I missed in the Escaping/Unescaping function

Because UnescapeScring wasn't exposed in C# I wrote a function :
static public string UnescapeString(string pszInput)
        {
             string pszOutput="";
            int iIn = 0;
            for (iIn = 0; iIn<pszInput.Length; iIn++)
            {
                if (pszInput[iIn] == '\\')
                {
                    iIn++;
                    if (pszInput[iIn] == 'n')
                        pszOutput += '\n';
                    else if (pszInput[iIn] == '0')
                        pszOutput += '\0';
                    else
                        pszOutput += pszInput[iIn];
                }
                else
                {
                    pszOutput += pszInput[iIn];
                }
            }
            return pszOutput;
        }

thanks in advance!
Best regards

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