cdm/src/main/java/ucar/nc2/iosp/nids/Nidsheader.java
public boolean isValidFile( ucar.unidata.io.RandomAccessFile raf) {
        try
        {
            long t = raf.length();
            if(t == 0){
                throw new IOException("zero length file ");
            }
        }
        catch ( IOException e )
        {
            return( false );
        }

        try{
            int p = this.readWMO( raf );
            if( p == 0 ) return false; // not unidata radar mosiac gini file
        }
        catch ( IOException e )
        {
            return( false );
        }
        return true;
    }
public boolean isValidFile( ucar.unidata.io.RandomAccessFile raf) {
        try
        {
            long t = raf.length();
            if(t == 0){
                throw new IOException("zero length file ");
            }
        }
        catch ( IOException e )
        {
            return( false );
        }

        try{
            int p = this.readWMO( raf );
            if( p == 0 ) return false; // not unidata radar mosiac gini file
        }
        catch ( IOException e )
        {
            return( false );
        }
        return true;
    }
check if this file is a nids / tdwr file
@param raf    input file
@return  true  if valid