#READ GRIDDED BINARY FILES


read_sint <- function(handle) {
    return(readBin(handle, "int", 1, size=4, signed = TRUE, endian = "big"));
}
read_uint <- function(handle) {
    return(readBin(handle, "int", 1, size=4, signed = FALSE, endian = "big"));
}
read_real <- function(handle) {
    return(readBin(handle, "numeric", 1, size=4, endian = "big"));
}
 
read_header <- function(handle) {
    len <- read_uint(handle);
    if( len < 8*4 ) {
        print("invalid file format");
        return(NA);
    }
        Mnow <- read_sint(handle);
    unk1 <- read_sint(handle);
    unk2 <- read_sint(handle);
    MONM <- read_sint(handle);
    unk3 <- read_sint(handle);
    IYRBEG <- read_sint(handle);
    BAD <- read_sint(handle);
    unk4 <- read_sint(handle);
    title <- rawToChar(readBin(handle, "raw", len-8*4));
    if( read_uint(handle) != len ) {
        print("invalid file format");
        return(NA);
    }
        return(pairlist(Mnow=Mnow, unk1=unk1, unk2=unk2, MONM=MONM, unk3=unk3, IYRBEG=IYRBEG, BAD=BAD, unk4=unk4, title=title));
}
read_record <- function(handle, Mnow) {
    len <- read_uint(handle);
    if( length(len) == 0 ) {
        # no more data
        return(NA);
    }
        if( len != (8+Mnow)*4 ) {
        print("invalid file format");
        return(NA);
    }
        Next <- read_sint(handle);
    LATS <- read_sint(handle);
    LATN <- read_sint(handle);
    LONW <- read_sint(handle);
    LONE <- read_sint(handle);
    NR1 <- read_sint(handle);
    NR2 <- read_sint(handle);
    DL <- read_sint(handle);
    temp_data <- readBin(handle, "numeric", Mnow, size=4, endian = "big");
    if( read_uint(handle) != len ) {
        print("invalid file format");
        return(NA);
    }
        return(pairlist(temp_data=temp_data, Next=Next, LATS=LATS, LATN=LATN, LONW=LONW, LONE=LONE, NR1=NR1, NR2=NR2, DL=DL));
}
 
read_GISS_data <- function(handle) {
    header_data <- read_header(handle);
    Mnow = header_data$Mnow;
    records <- vector("pairlist", 1);
    num <- 1;
    while(TRUE) {
        record <- read_record(handle, Mnow);
        if( length(record) == 1 ) {
            return(pairlist(header=header_data, records=records));
        } else {
                        records[[num]] = record;
                        num <- num+1;
            Mnow = record$Next;
        }
    }
}

##MAKE GRID INFO
 make.grid.info=function (Data){ 
	f=function(X) unlist(X[2:9])
	grid.info=sapply(Data[[2]],f)
	grid.info=t(grid.info)
	grid.info=data.frame(grid.info)
		#the params LATS, LATN, LONW,LONE define the four parameters of the box
		#decimal values appear to be used
	grid.info[,2:5]=grid.info[,2:5]/10
		#order1=order(-grid.info$LATS,grid.info$LONW)
		#grid.info[order1,][1:100,]
	make.grid.info=grid.info
	make.grid.info
	}

  hansenbox=function(lat,long) (1:8000)[(grid.info$LATS<=lat)&(grid.info$LATN>lat)&(grid.info$LONW<=long)&(grid.info$LONE>long)]