Merge rasters by GDAL

at National Taiwan University

Year:2021

ArcMap

Python

Description

This is short python script for mergin multiple raster together.

Problem statment:

If we need to merge multiple rasters together we normally use Mosaic To New Raster tool.

This function doesn't work well with a large number of datasets or if the final GeoTIFF is too large.

Therefore, it's better to use a python script to do the hard work for us.

eg. In Taiwan, the DEM raster comes in multiple grid files together with a shapefile which includes the grid filenames

Figure 1: Raster grids

How I did it:

First I used the selected area shapefile to clip the grid shapefile.

Second, I exported an attribute table, where each polygon has a grid field.

In the last step, I built this small script which is based on the osgeo.gdal library.

Python script:

from osgeo import gdal
import pandas as pd
import os

#read csv table 
files = pd.read_csv("table_from_shapefile.csv")
#take only grid column as it contains the name of files
filenames = files["grids"]

#make a list of filenames
demnames = []
for names in filenames:
    name = "Grid/"+str(names)+"DEM.tif"
    #check if file exists, if so, append to list
    if os.path.exists(name) == True:
         demnames.append(name)

#copy demnames
files_to_mosaic = demnames
g = gdal.Warp("output.tif", files_to_mosaic, format="GTiff",
              options=["COMPRESS=LZW", "TILED=YES"]) 

# Close file and flush to disk
g = None 

Results: