Using Python GDAL Merge (gdal_merge.py)

Question

I am having a Merging issue with the GDAL python library. I am using gdal_merge.pylink

My issue is when I merge two rasters NoData value of one raster overlaps the other data resulting in not a proper raster image.

For example, in the raster images below (left images) if I merge these 4 images labeled as 1,2,3,4 I should get the merged raster image as the right-sided image.

enter image description here

enter image description here

But, the merged image I am getting looks like this (image below):

(Note: Image labeled 1,2 and 3 are merged properly. It's only when we merged them with image labeled 4, it's not properly merging.)

enter image description here

How do I resolve this issue?

Answer 1

If you are not using the -n parameter, nodata values will be included in your mosaic.

GDAL will ignore nodata values if you specify this and will mosaic data without overlapping nodata areas included.

Note (update from OP): np.nan may not work as a nodata value

For example:

gdal_merge.py -n 0 -o output.tif input1.tif input2.tif

You will need to know the nodata value and make sure it is the same in each image

• terraCoder: Hi @NathanThomas, I am using -n parameter. import gdal_merge as gm , gm.main(['', '-o', outPath, '-of', 'GTiff', '-init', 'np.nan', '-n', 'np.nan', '-a_nodata', 'np.nan', 'input1.tif', 'input2.tif', 'input3.tif', 'input4.tif'])
• GeoMonkey: Is the nodata value in each image a nan value?
• terraCoder: Yes, All the images have nodata as nan value.
• GeoMonkey: This is strange. Can you include more of your code in the question?
• terraCoder: Looks like I have found the problem. It was not working properly becasue of NaN values. gdal_merge.py doesn't support the NaN values. I have change nodata from NaN (np.nan) to -9999 and it workds. Thanks for the help.