Example C# code to directly change existing LiDAR LAS file field values

For more efficient manipulation of LiDAR LAS files, C# can be used to directly change values in binary LAS files. Here is a simple example code snippet for locating and changing the Z bounding range fields of an existing LiDAR LAS file.

Essentially, the LAS file has to be opened as a binary file stream first. Then the file stream pointer has to be moved to the correct starting offset of a field before you can change the field values of the existing LAS file using the binary writer's write method. You have to ensure the C# data types match the LAS file fields though. In this case, the starting offsets for the Max Z and Min Z fields (doubles at 8 bytes each) are at  211 and 219 bytes respectively.

For more details about the LAS fields and the byte offsets, click on this link http://liblas.org/development/specifications.html.

double maxz, minz;
//....etc....
//Somewhere here the Z bounding range (minz and maxz) is calculated

//Open a file stream to the LAS file
FileStream fs = File.Open(@"C:\Temp\file.las", FileMode.Open);
if (fs.CanSeek)
{
    BinaryWriter binWriter = new BinaryWriter(fs);
    //move to the location of the maxz field in the LAS file
    fs.Seek(211, SeekOrigin.Begin); 
    //Write the maxz double value to the LAS file
    binWriter.Write(maxz);
    //move to the location of the minz field in the LAS file
    fs.Seek(219, SeekOrigin.Begin); 
    //Write the minz double value to the LAS file
    binWriter.Write(minz);
    //Close the writer
    binWriter.Close();
}
//Close the LAS file
fs.Close();
}