I am using piexif library to modify the gps altitude of a tif file's EXIF data. This is my implementation:
import piexif
from PIL import Image
Image.MAX_IMAGE_PIXELS = 1000000000
fname_1='initial.tif'
fname_2='new_file.tif'
img = Image.open(fname_1)
exif_dict = piexif.load(fname_1)
new_exif_dict = exif_dict
new_exif_dict['GPS'][piexif.GPSIFD.GPSAltitude] = (140, 1)
del new_exif_dict['0th'][50714] # I delete this because it causes an error for class type for some reason. It happens even if I dump the original metadata as they are, to a new tif file
exif_bytes = piexif.dump(new_exif_dict)
im = Image.open(fname_1)
im.save(fname_2, exif=exif_bytes)
The code works, however the metadata are now a lot less on the new tif photo than the original one. Even the GPS coordinates are lost.
My question is how could I change the tif file's metadata about GPS without affecting the rest?
Using PIL and saving the image will recompress the data and rewrite or remove many tags. You can use a different library that alters less. For instance, if you are only working with tiff files, you can do this with the tifftools python package via the command line:
tifftools set --set GPSAltitude,0,GPSIFD:0 140,1 IMG_0036_1.tif new_file.tif
or via python:
import tifftools
# Load all tag information from the file
info = tifftools.read_tiff('IMG_0036_1.tif')
# Get a reference to the IFD with GPS tags. If the GPS data is in a different
# location, you might need to change this.
gpsifd = info['ifds'][0]['tags'][tifftools.Tag.GPSIFD.value]['ifds'][0][0]
# Set the altitude tag; this assumes it already exists and is stored as a rational
gpsifd['tags'][tifftools.constants.GPSTag.GPSAltitude.value]['data'] = [140, 1]
# Write the output; this copies all image data from the original file.
tifftools.write_tiff(info, 'new_file.tif')
Disclaimer: I'm the author of tifftools.