[Gwyddion-users] Mutual crop and cross correlation for VSI data

[Erika Callagon]

I want to do a Mutual Crop on my VSI .dat images to remove lateral shifts
between the two images. I have successfully done this with other data, but
I don't know why it I can't do it for the two new images that I have. When
I go to 'cross-correlation', the 'Correlate with' drop down option is
disabled (the other options are active). The images are taken with the same
setup, and should have the same dimension of pixels. Do you have any
advice? Thank you!

-Erika

[Erika Callagon]

I'd also like to add that I get this following messages when doing this:

GwyProcess-CRITICAL: gwy_data_field_get_val: assertion
'gwy_data_field_inside(data_field, col, row)' failed
GwyProcess-CRITICAL: Last message repeated 13 times

Thanks again!

-Erika

Post by Erika Callagon
I want to do a Mutual Crop on my VSI .dat images to remove lateral shifts
between the two images. I have successfully done this with other data, but
I don't know why it I can't do it for the two new images that I have. When
I go to 'cross-correlation', the 'Correlate with' drop down option is
disabled (the other options are active). The images are taken with the same
setup, and should have the same dimension of pixels. Do you have any
advice? Thank you!
-Erika

[David Nečas (Yeti)]

Post by Erika Callagon
GwyProcess-CRITICAL: gwy_data_field_get_val: assertion
'gwy_data_field_inside(data_field, col, row)' failed
GwyProcess-CRITICAL: Last message repeated 13 times

This is odd. No correlation module should even use
gwy_data_field_get_val().

When does the message really appear? You can keep the Program Messages
window open to see immediately when it appears.

Regards,

Yeti


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[Erika Callagon]

Thank you very much. I can't reproduce the error message - it's probably
from something else.

-Erika

Post by David Nečas (Yeti)

Post by Erika Callagon
GwyProcess-CRITICAL: gwy_data_field_get_val: assertion
'gwy_data_field_inside(data_field, col, row)' failed
GwyProcess-CRITICAL: Last message repeated 13 times

This is odd. No correlation module should even use
gwy_data_field_get_val().
When does the message really appear? You can keep the Program Messages
window open to see immediately when it appears.
Regards,
Yeti
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[David Nečas (Yeti)]

Post by Erika Callagon
I want to do a Mutual Crop on my VSI .dat images to remove lateral shifts
between the two images. I have successfully done this with other data, but
I don't know why it I can't do it for the two new images that I have. When
I go to 'cross-correlation', the 'Correlate with' drop down option is
disabled (the other options are active). The images are taken with the same
setup, and should have the same dimension of pixels.

For correlation the images do not need the same pixel dimensions.
Instead one pixel must represent the same area in both (otherwise the
correlation makes no sense). In other words, the ratio of physical size
in metres and pixel resolution must be the same for both images.

You can make the images compatible by resampling one (presumably that
with larger pixels) using Scale. It only changes the pixel resolution,
leaving physical dimensions intact.

If you did that and the images still do not seem compatible you can use
Match pixel size in Dimensions and Units to enforce equal pixel sizes.
Only do this after you ensured the pixel sizes are equal, but some
minuscule differences possibly remain due to rounding.

Regards,

Yeti


P.S.: The other two compatility conditions for Mutual Crop are that the
dimensions and values have the same units for both images – but I
suppose you do not have problem with that.

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