Parallel curved lines using GIMP.
Posted 16 December 2008 - 05:58 PM
Posted 16 December 2008 - 06:00 PM
Posted 16 December 2008 - 07:24 PM
Identical curves offset from each other are not parallel (if they are in the same plane).
I would recommend creating a path to represent the center-line of your tracks. Create a new Channel and stroke the path in white with a width equal to the desired distance between the tracks. Now convert that channel into a selection (using the red square button next to the trash can at the bottom of the Channels Dialog), create a new transparent layer, and stroke the selection with the color and width of your tracks. (You may need to clean up the stroked selection at the edges of the image, or work on a slightly larger image and crop it afterwards.)
Posted 16 December 2008 - 10:15 PM
After that turn the selection into a path selection>to path, Then release the selection, create a new layer, and stroke the new path on the new layer, with about 5 pixels.
You could then just cut off the starting points from the final image.
Posted 17 December 2008 - 05:00 AM
Posted 18 December 2008 - 01:24 AM
I don't know what I'm doing wrong but this absolutely has me totally befuddled.
- [*:79g0t1su]I made a path
[*:79g0t1su]I created a new Channel
[*:79g0t1su]I stroked the path
[*:79g0t1su]Converting the channel into a selection would not work for me.
[*:79g0t1su]So nothing beyond this point happened.
I ended up doing everything from the Paths dialog which worked fine. Using GIMP 2.4.7 in Fedora 8
Posted 18 December 2008 - 04:42 AM
Posted 18 December 2008 - 07:42 AM
I would like to try and understand what the channels dialog does but it just baffles me.
Posted 18 December 2008 - 07:58 AM
Oh. I misread what you had written. In step #3, you're supposed to stroke the selection, not the path.
Perhaps it would be more understandable if you used the QuickMask instead.
- [*:1v9jo6hj]Create your path.
[*:1v9jo6hj]Set the FG color to white.
[*:1v9jo6hj]Active the Quickmask and stroke the path ("Edit->Stroke Path...") with a very large width.
[*:1v9jo6hj]Deactivate Quickmask, set the FG to the color you want your tracks, and stroke the selection ("Edit->Stroke Selection...") with a narrow width.
The QuickMask is just a channel which is created from the selection when you activate it; and when deactivated, the channel replaces the selection and is deleted automatically (you can see this if your Channels Dialog is open).
Posted 18 December 2008 - 04:26 PM
OK, I clicked the red button in the Channels dialog and the thick white line is selected. I have the selection now and I don't know where to go to stroke the selection. I can't find an option anywhere to do that.
Going to Edit > Stroke Selection ... I changed the fg color to red and the width of the stroke to 5 ... it doesn't stroke the selection. I get nothing with that step.
OK, I uploaded the xcf file with the selection still in place.
LATER: After closing the xcf file, I reopened it and it stroked with the red just fine. Sometimes things quit working in GIMP for me. Don't know why. It's not a memory problem I'm sure. I have 2gb of RAM.
I would certainly like to understand Channels better. The Paths dialog I love and use it a lot.
Posted 18 December 2008 - 07:30 PM
I will surmise that you did not create a new transparent layer as indicated in my original instructions, but instead were attempting to stroke the red lines onto an existing layer. If so, then you need to make that layer active before stroking the selection, otherwise the channel is the active drawable and your red stroke will be painted on the channel (creating a new layer automatically makes that new layer the active drawable so I failed to state that as an explicit step).
What is occurring here is that when your XCF file is loaded, all of the channels, layers, paths, and selections are restored; however, the active drawable at the time of saving is NOT restored and instead GIMP sets the top layer in the layerstack active. Therefore, you have effectively activated the appropriate layer.
Channels are indeed useful. One must be careful about whether a channel or a layer (or a layermask) is active whenever one does any drawing (painting, filling, stroking, etc). It is often necessary to re-activate your layer after, for example, saving your selection to a channel because this sets the created channel active (I wonder if it would not be more useful if the original layer remained active when this is done, maybe I will submit a patch :) ).
Posted 18 December 2008 - 07:43 PM
I think what I did was make the new layer first. That probably explains a lot.
LATER: Well will ya look at that! AFTER clicking the red button in the Channels dialog, went back to Layers, made a new layer, Stroked the selection and Voila! Woooooo Hoooooooo!!!
Takes me awhile.
Posted 22 December 2008 - 06:32 PM
There is another forum at http://www.cartographersguild.com that focuses on cartography and mapping. There are a fair number of gimp users (myself included) that may be able to provide tips specific to mapping!
The simplest way is to stoke the path once with your colour then stroke again with a narrower brush either with the eraser or with the paintbrush in the background colour.
Also, if you want to make ties on the track, create an angular gih brush and stroke the path a third timewith that:
Posted 22 December 2008 - 07:41 PM
Or I could provide a way of doing it using the GAP's Move Path command which only entails about 20 steps, requires 2gig of RAM, and produces a less favorable result. :lol:
Posted 22 December 2008 - 08:50 PM
ROFL!! Good one!