[GRASS-user] Rotating raster maps

GRASS GRASS user
1

   I have .tif images at 1:5000 or 1:6000 scale that are each slightly
rotated clockwise on their rectangular backgrounds. The imported raster maps
are also slightly torqued so edges do not properly align (see attached
screenshot).

   Is there an i.* module that can rotate them so when patched together there
are no gaps?

Rich

(attachments)

screenshot.png

2

On Wed, Jul 18, 2018 at 2:53 PM, Rich Shepard <rshepard@appl-ecosys.com> wrote:

  I have .tif images at 1:5000 or 1:6000 scale that are each slightly
rotated clockwise on their rectangular backgrounds. The imported raster maps
are also slightly torqued so edges do not properly align (see attached
screenshot).

  Is there an i.* module that can rotate them

Yes:
https://grass.osgeo.org/grass74/manuals/addons/#i
-> i.rotate

Markus

so when patched together there
are no gaps?

Rich
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3

But are those tif images? Or GeoTiff? Because, if those are geotiffs, with correct georeferencing, I believe rotating will mess things up.

On Wed, Jul 18, 2018 at 11:48 AM Markus Neteler <neteler@osgeo.org> wrote:

On Wed, Jul 18, 2018 at 2:53 PM, Rich Shepard <rshepard@appl-ecosys.com> wrote:

I have .tif images at 1:5000 or 1:6000 scale that are each slightly
rotated clockwise on their rectangular backgrounds. The imported raster maps
are also slightly torqued so edges do not properly align (see attached
screenshot).

Is there an i.* module that can rotate them

Yes:
https://grass.osgeo.org/grass74/manuals/addons/#i
→ i.rotate

Markus

so when patched together there
are no gaps?

Rich

grass-user mailing list
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4

On Wed, 18 Jul 2018, Markus Neteler wrote:

Yes:
https://grass.osgeo.org/grass74/manuals/addons/#i
-> i.rotate

Markus,

   Thanks. It's been a very long time since I worked with remotely acquired
imagery.

Much appreciated,

Rich

5

On Wed, 18 Jul 2018, Daniel Victoria wrote:

But are those tif images? Or GeoTiff? Because, if those are geotiffs, with
correct georeferencing, I believe rotating will mess things up.

Daniel,

   Probably GeoTIFF. If rotating is not the solution is there another way to
patch them together without thin wedges?

Regards,

Rich

6

Some satellite images comes rotated, with black borders. But if we rotate them prior to patching, we mess up the georeferencing. The process then is setting those borders to null and then patching.

If this is your case, then I’d try running r.null to set those borders as no-data and then use r.patch.

But again, not sure if this is your case

Cheers

On Wed, Jul 18, 2018 at 12:06 PM Rich Shepard <rshepard@appl-ecosys.com> wrote:

On Wed, 18 Jul 2018, Daniel Victoria wrote:

But are those tif images? Or GeoTiff? Because, if those are geotiffs, with
correct georeferencing, I believe rotating will mess things up.

Daniel,

Probably GeoTIFF. If rotating is not the solution is there another way to
patch them together without thin wedges?

Regards,

Rich

grass-user mailing list
grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

7

On Wed, 18 Jul 2018, Daniel Victoria wrote:

Some satellite images comes rotated, with black borders. But if we rotate
them prior to patching, we mess up the georeferencing. The process then is
setting those borders to null and then patching.

If this is your case, then I'd try running `r.null` to set those borders as
no-data and then use `r.patch`.

But again, not sure if this is your case

Daniel,

   Worth a try.

Thanks,

Rich