2

I have the following piece of rasterio Python code, to read in a tiffs with discrete integer classes, which I mask immediately upon loading. I need finegrained control over the nodata value, which needs to be the same regardless of the input data type.

import rasterio from rasterio.mask import mask #[...] with rasterio.open(Geotiff_path) as src: cropped_image, _ = mask(src, POL, nodata=128, crop=True, all_touched=True ) return cropped_image.squeeze()

The problem is that if print(src.dtypes) is int8, the nodata=128 overflows back to -128. Of course, one fix is to simply use nodata=127. However, I would prefer it if it were possible to return the cropped_image with a different dtype such as int16, wherein the nodata didn't overflow.

Note that doing cropped_image.squeeze().astype(np.uint16) does the transformation too late, i.e., the overflow of the nodata value to -128 already happened. So the question is: how can I read in the rasterio grid (or the masked version) with a different dtype than the original grid reports?

I'm using rasterio==1.2.10.

Improve this question
0

1 Answer 1

Reset to default
3

Don't specify nodata=128. If filled=False, mask returns a np.ma.MaskedArray which you can cast to np.uint16 then set all values to 128 where the mask is True:

import fiona import rasterio from rasterio.mask import mask with fiona.open("/tmp/mask.shp", "r") as shapefile: shapes = [feature["geometry"] for feature in shapefile] with rasterio.open("/tmp/test.tif") as src: out_image, out_transform = mask(src, shapes, crop=True, filled=False, all_touched=True) data = out_image.data.astype('uint16') data[out_image.mask] = 128

Alternatively, use a WarpedVRT to alter dtype on the fly:

import fiona import rasterio from rasterio.mask import mask from rasterio.vrt import WarpedVRT with fiona.open("/tmp/mask.shp", "r") as shapefile: shapes = [feature["geometry"] for feature in shapefile] with WarpedVRT(rasterio.open("/tmp/test.tif"), dtype='uint16') as vrt: out_image, out_transform = mask(vrt, shapes, nodata=128, crop=True, all_touched=True)
Improve this answer

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.