Resizing or scaling a replacement background image
Hello everyone - I am not sure how this should be handled, or if it even CAN be handled ... A few weeks ago we went to a section of a cave where the original sketch has some problems. Rather than resketch the entire section, we took the original sketch and made corrections directly on it. Now I want to update the Therion map. Six months ago I used the original sketch as the background of a .th2 file, then drew as much as I could figure out. Since the update is on the same piece of paper, I figured I could just replace the original drawing background with a scanned image of the updated sketch. It did not work. The new scanned background comes in about 1/5 as big as it needs to be. The original elements I drew do not match up, so I cannot draw the new stuff on it. I think the reason is that the original background and the new background were scanned at different resolutions. I did not scan them. The old background image is 2550x3300 pixels and the new is 908x1200 pixels. What do you suggest? Is there a way to stretch the new background so it fits under the existing drawing? It might be easiest to ask for a rescan. The new scan might still not line up. Is there a way to shift the background? I think there is. I have managed to do it a few times by accident. No idea what keys I hit when that happens. I have to close the .th2 without saving, then open and start again. -- =============== Bill Gee
I have Inkscape but have never used it for cave cartography. I do not have the Therion plugin for it. The regular xTherion interface is familiar and generally suitable, so I have never felt the need to go through another learning curve. =============== Bill Gee On 4/4/26 00:54, Axel via Therion wrote:
Moin, scaling (multiple) backgrounds are no problem if u use Inkscape with the Therion plugin (one of the reasons I startet using it) I know it has other issues and misses some features u use, but it might be a solution here...
Axel *Gesendet: *Freitag, 3. April 2026 um 19:45 *Von: *"Bill Gee" <bgee@campercaver.net> *An: *"Therion Mail List" <therion@speleo.sk> *Betreff: *[Therion] Resizing or scaling a replacement background image Hello everyone -
I am not sure how this should be handled, or if it even CAN be handled ...
A few weeks ago we went to a section of a cave where the original sketch has some problems. Rather than resketch the entire section, we took the original sketch and made corrections directly on it.
Now I want to update the Therion map. Six months ago I used the original sketch as the background of a .th2 file, then drew as much as I could figure out. Since the update is on the same piece of paper, I figured I could just replace the original drawing background with a scanned image of the updated sketch. It did not work.
The new scanned background comes in about 1/5 as big as it needs to be. The original elements I drew do not match up, so I cannot draw the new stuff on it.
I think the reason is that the original background and the new background were scanned at different resolutions. I did not scan them. The old background image is 2550x3300 pixels and the new is 908x1200 pixels.
What do you suggest? Is there a way to stretch the new background so it fits under the existing drawing?
It might be easiest to ask for a rescan. The new scan might still not line up. Is there a way to shift the background? I think there is. I have managed to do it a few times by accident. No idea what keys I hit when that happens. I have to close the .th2 without saving, then open and start again.
-- =============== Bill Gee
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_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
On Saturday, April 4th, 2026 at 8:30 AM, Bill Gee <bgee@campercaver.net> wrote:
I have Inkscape but have never used it for cave cartography. I do not have the Therion plugin for it. The regular xTherion interface is familiar and generally suitable, so I have never felt the need to go through another learning curve.
I would love to say that resizing and moving of background images is available on Mapiah but that is not true yet. Just included it on the TODO list. I expect that next version will support these actions. Regards, Rodrigo
=============== Bill Gee
On 4/4/26 00:54, Axel via Therion wrote:
Moin, scaling (multiple) backgrounds are no problem if u use Inkscape with the Therion plugin (one of the reasons I startet using it) I know it has other issues and misses some features u use, but it might be a solution here...
Axel *Gesendet: *Freitag, 3. April 2026 um 19:45 *Von: *"Bill Gee" <bgee@campercaver.net> *An: *"Therion Mail List" <therion@speleo.sk> *Betreff: *[Therion] Resizing or scaling a replacement background image Hello everyone -
I am not sure how this should be handled, or if it even CAN be handled ...
A few weeks ago we went to a section of a cave where the original sketch has some problems. Rather than resketch the entire section, we took the original sketch and made corrections directly on it.
Now I want to update the Therion map. Six months ago I used the original sketch as the background of a .th2 file, then drew as much as I could figure out. Since the update is on the same piece of paper, I figured I could just replace the original drawing background with a scanned image of the updated sketch. It did not work.
The new scanned background comes in about 1/5 as big as it needs to be. The original elements I drew do not match up, so I cannot draw the new stuff on it.
I think the reason is that the original background and the new background were scanned at different resolutions. I did not scan them. The old background image is 2550x3300 pixels and the new is 908x1200 pixels.
What do you suggest? Is there a way to stretch the new background so it fits under the existing drawing?
It might be easiest to ask for a rescan. The new scan might still not line up. Is there a way to shift the background? I think there is. I have managed to do it a few times by accident. No idea what keys I hit when that happens. I have to close the .th2 without saving, then open and start again.
-- =============== Bill Gee
_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion <https://mailman.speleo.sk/ listinfo/therion>
_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
What about using imagemagick to resize the new image? magick new_sketch.jpg -resize 2550x3300! fixed_sketch.png Henry On Fri, 3 Apr 2026 at 18:53, Bill Gee <bgee@campercaver.net> wrote:
Hello everyone -
I am not sure how this should be handled, or if it even CAN be handled ...
A few weeks ago we went to a section of a cave where the original sketch has some problems. Rather than resketch the entire section, we took the original sketch and made corrections directly on it.
Now I want to update the Therion map. Six months ago I used the original sketch as the background of a .th2 file, then drew as much as I could figure out. Since the update is on the same piece of paper, I figured I could just replace the original drawing background with a scanned image of the updated sketch. It did not work.
The new scanned background comes in about 1/5 as big as it needs to be. The original elements I drew do not match up, so I cannot draw the new stuff on it.
I think the reason is that the original background and the new background were scanned at different resolutions. I did not scan them. The old background image is 2550x3300 pixels and the new is 908x1200 pixels.
What do you suggest? Is there a way to stretch the new background so it fits under the existing drawing?
It might be easiest to ask for a rescan. The new scan might still not line up. Is there a way to shift the background? I think there is. I have managed to do it a few times by accident. No idea what keys I hit when that happens. I have to close the .th2 without saving, then open and start again.
-- =============== Bill Gee
_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
I think the reason is that the original background and the new background were scanned at different resolutions. I did not scan them. The old background image is 2550x3300 pixels and the new is 908x1200 pixels.
What do you suggest? ... Rescan the original with the same settings originally used (preferred), else use a tool to resize the image, as suggested by others (likely to not be perfect).
The new scan might still not line up. Is there a way to shift the background? It likely will not. Double right-click and drag allows you to move the background image. Bruce
Hi Bruce - I got a rescanned image from the man who has the originals. It is not quite exactly the same pixel size as the first, but darn close. As predicted, the background does not line up with the objects I have already drawn. I tried your method - double-right-click and then drag. Does not work. Dragging moves both the background image and the drawn objects. Same for double-left-click and then drag. I am double-clicking on the background image. Is that the right place? It looks like I could get it aligned by adjusting the parameters on "Move To". It would take some fiddling. =============== Bill Gee On 4/5/26 23:33, bruce@tomo.co.nz wrote:
I think the reason is that the original background and the new background were scanned at different resolutions. I did not scan them. The old background image is 2550x3300 pixels and the new is 908x1200 pixels.
What do you suggest? ... Rescan the original with the same settings originally used (preferred), else use a tool to resize the image, as suggested by others (likely to not be perfect).
The new scan might still not line up. Is there a way to shift the background? It likely will not. Double right-click and drag allows you to move the background image.
Bruce
_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
It is not quite exactly the same pixel size as the first, but darn close. I find that to be the case sometimes. In which case I move the background image slightly depending on where exactly on the image I am drawing/tracing.
I am double-clicking on the background image. Is that the right place? Yes, you need to double right-click on a non-blank pixel that is part of that particular image (xvi or other bitmap type). It often takes me several attempts. When you have it, the cursor changes from a white cross (single right-click for panning) to a white four headed arrow.
I have tried to screen shot it, but Windows 11 has broken the delay on the snipping tool in the last few days/weeks it seems. Bruce -----Original Message----- From: Therion <therion-bounces@speleo.sk> On Behalf Of Bill Gee Sent: Tuesday, 7 April 2026 23:33 To: therion@speleo.sk Subject: Re: [Therion] Resizing or scaling a replacement background image Hi Bruce - I got a rescanned image from the man who has the originals. It is not quite exactly the same pixel size as the first, but darn close. As predicted, the background does not line up with the objects I have already drawn. I tried your method - double-right-click and then drag. Does not work. Dragging moves both the background image and the drawn objects. Same for double-left-click and then drag. I am double-clicking on the background image. Is that the right place? It looks like I could get it aligned by adjusting the parameters on "Move To". It would take some fiddling. =============== Bill Gee On 4/5/26 23:33, bruce@tomo.co.nz wrote:
I think the reason is that the original background and the new background were scanned at different resolutions. I did not scan them. The old background image is 2550x3300 pixels and the new is 908x1200 pixels.
What do you suggest? ... Rescan the original with the same settings originally used (preferred), else use a tool to resize the image, as suggested by others (likely to not be perfect).
The new scan might still not line up. Is there a way to shift the background? It likely will not. Double right-click and drag allows you to move the background image.
Bruce
_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
_______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
participants (5)
-
Axel -
Bill Gee -
bruce＠tomo.co.nz -
Henry Bennett -
Rodrigo Severo