Python计算多幅图像栅格值的平均值

import os
import os.path
import gdal
import sys
from gdalconst import *
from osgeo import gdal
import osr
import numpy as np
#coding=utf-8

def writegtifffile(filename, nrows, ncols, data,geotrans,proj, nodatavalue, gdaltype):#向磁盘写入结果文件
    format = "gtiff"   
    driver = gdal.getdriverbyname(format)
    ds = driver.create(filename, ncols, nrows, 1, gdaltype)
    ds.setgeotransform(geotrans)
    ds.setprojection(proj)
    ds.getrasterband(1).setnodatavalue(nodatavalue)
    ds.getrasterband(1).writearray(data)    
    ds = none

def file():#遍历文件，读取数据，算出均值
    rows,cols,geotransform,projection,nodatavalue = readxy('e://work//evi_data_tif//20006.tif')
    #获取源文件的行，列，投影等信息，所有的源文件这些信息都是一致的
    print 'rows and cols is ',rows,cols
    filesum = [[0.0]*cols]*rows #栅格值和，二维数组
    average= [[0.0]*cols]*rows# 存放平均值，二维数组
    filesum=np.array(filesum)#转换类型为np.array
    average = np.array(average) 
    print 'the type of filesum',type(filesum)
    count=0
    rootdir = 'e:\work\evi_data_tif'
    for dirpath,filename,filenames in os.walk(rootdir):#遍历源文件
        for filename in filenames:
            if os.path.splitext(filename)[1] == '.tif':#判断是否为tif格式
                filepath = os.path.join(dirpath,filename)
                purename = filename.replace('.tif','') #获得除去扩展名的文件名，比如201013.tif，purename为201013               
                if purename[:4] == '2010':              #判断年份
                    filedata = [[0.0]*cols]*rows
                    filedata = np.array(filedata)
                    filedata = read(filepath)           #将2010年的13幅图像数据存入filedata中
                    count+=1
                    np.add(filesum,filedata,filesum)    #求13幅图像相应栅格值的和
                    #print str(count)+'this is filedata',filedata
    print 'count is ',count    
    for i in range(0,rows):
        for j in range(0,cols):
            if(filesum[i,j]==nodatavalue*count):        #处理图像中的nodata
                average[i,j]=-9999
            else: 
                average[i,j]=filesum[i,j]*1.0/count     #求平均
    writegtifffile("e:\\work\\result\\2010.tif", rows, cols, average,geotransform,projection, -9999, gdt_float32) #写入结果文件           

def readxy(rasterfile): #读取每个图像的信息     
    ds = gdal.open(rasterfile,ga_readonly)
    if ds is none:
        print 'cannot open ',rasterfile
        sys.exit(1)
    cols = ds.rasterxsize
    rows = ds.rasterysize
    band = ds.getrasterband(1)
    data = band.readasarray(0,0,cols,rows)
    nodatavalue = band.getnodatavalue()
    projection=ds.getprojection()
    geotransform = ds.getgeotransform()
    return rows,cols,geotransform,projection,nodatavalue

def read(rasterfile):#读取每个图像的信息
    ds = gdal.open(rasterfile,ga_readonly)    
    if ds is none:
        print 'cannot open ',rasterfile
        sys.exit(1)
    cols = ds.rasterxsize
    rows = ds.rasterysize
    band = ds.getrasterband(1)
    data = band.readasarray(0,0,cols,rows)  
    return data    
if __name__ == "__main__":
    print"ok1"
    file()   
    print"ok2"