Maintaining raster grid when clipping

[Nathan Thomas]

Hi Dan/Pete,

I have two rasters Image1 and Image2. Image1 is a local country sized dataset and Image2 is a global dataset. I want to subset Image2 to where Image1 is valid - for example '(b1==1)?b2:0'. Although the same images are the same projection and resolution they are not the same extent and I can't guarantee that they are on the same grid. I would like to subset Image2 to get Image3, but I want Image3 to have the same grid as Image2. I ideally don't want to use the CreateCopyImageCommand as this will give me a lot of global sized rasters and I want the extent to be that of the smaller image. Do you know of a way that I could subset a larger image by a smaller image, whilst maintaining the grid (but not extent) of the larger image?

I know RIOS has a 'setReferenceImage' command but this also keeps the extent of the larger image.

Cheers, Nathan

[Peter Bunting]

Hi Nathan, 

Just use 

rsgislib.imageutils.subset2img(inputimage, inputROIimage, outputimage, gdalformat, type)

The grid of the output image will be the same as the input with just the extent from the ROI image. 

To use the two images together you’ll have to put them on the same grid, RSGISLib just does the nearest - to effectively nearest neighbour interpolation if you were to resample the second image.

Cheers, Pete

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[Nathan Thomas]

Hi Pete,

Thanks. This is useful for subsetting one image by another, but I was hoping to mask the image at the same time. I am looking for a way to keep the grid of the larger image but subset and mask it using the smaller image. Does that make sense?

Thanks, Nathan

On 3 July 2018 at 04:46, Peter Bunting <peteb...@gmail.com> wrote:

Hi Nathan, 

Just use 

rsgislib.imageutils.subset2img(inputimage, inputROIimage, outputimage, gdalformat, type)

The grid of the output image will be the same as the input with just the extent from the ROI image. 

To use the two images together you’ll have to put them on the same grid, RSGISLib just does the nearest - to effectively nearest neighbour interpolation if you were to resample the second image.

Cheers, Pete

On 2 Jul 2018, at 21:02, Nathan Thomas <nmtho...@gmail.com> wrote:

Hi Dan/Pete,

I have two rasters Image1 and Image2. Image1 is a local country sized dataset and Image2 is a global dataset. I want to subset Image2 to where Image1 is valid - for example '(b1==1)?b2:0'. Although the same images are the same projection and resolution they are not the same extent and I can't guarantee that they are on the same grid. I would like to subset Image2 to get Image3, but I want Image3 to have the same grid as Image2. I ideally don't want to use the CreateCopyImageCommand as this will give me a lot of global sized rasters and I want the extent to be that of the smaller image. Do you know of a way that I could subset a larger image by a smaller image, whilst maintaining the grid (but not extent) of the larger image?

I know RIOS has a 'setReferenceImage' command but this also keeps the extent of the larger image.

Cheers, Nathan

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[Peter Bunting]

HI Nathan, 

If you use the mask command then that will do what you want cutting to the common extent.

rsgislib.imageutils.maskImage(inputimage, imagemask, outputimage, gdalformat, datatype, outvalue, maskvalue)

Cheers, Pete

[Nathan Thomas]

Awesome, thanks Pete. I'll give it a go!

Nathan