how do I draw tapering latitudinal lines on a globe ?

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solo
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how do I draw tapering latitudinal lines on a globe ?

Post by solo » Sat Feb 03, 2018 1:11 am

Hi I am using windows 7 and Qcad 3.17 and I am trying to draw a globe with tapering latitudinal and longitudinal lines. The longitudinal (pole to pole arch's with decreasing spacing between the pairs as they move away from the center, then fill in the pairs to make tapered lines ) was not too difficult , but the latitudinal ellipse pairs have me stopped , also the globe is made from closely (but random ) spaced lines .
Any thoughts on the matter would be appreciated

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Husky
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by Husky » Sat Feb 03, 2018 2:22 am

Hello solo - welcome to the QCAD forum.
solo wrote:... but the latitudinal ellipse pairs have me stopped
There are a ton of different styles out there to draw a globe. To help you efficient we need to see an example, drawing or screenshot. My first idea would be to use a spline but again - we need more info. Thanks.
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solo
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by solo » Sat Feb 03, 2018 7:35 pm

The longitudinal lines look like this ( before filling )
2018-02-03_12-21-01.png
the latitudinal lines would be like on a globe of the earth . the last reply was deleted for too few words but I have no idea how many is enough and I don't want to do this a third time , marry had a little lamb his fleece was wight as snow ..............................................................................................................................

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Husky
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by Husky » Sat Feb 03, 2018 8:26 pm

Hello solo,

unfortunately your png isn't uploaded. Please follow this steps to attach a pic. Thanks.

viewtopic.php?f=47&t=3760
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Husky
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by Husky » Sun Feb 04, 2018 5:43 am

Comes this close to that what you are looking for?
Husky-2018.02.03-01.png
Husky-2018.02.03-01.png (49.09 KiB) Viewed 1145 times
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solo
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by solo » Mon Feb 05, 2018 3:02 pm

Thank you for the reply but those are longitudinal lines not latitudinal and your latitudinal lines are just straight horizontal lines
I need elliptical "Horizontal" lines in tapered pairs .
2018-02-03_12-21-01.png
2018-02-03_12-21-01.png (41.3 KiB) Viewed 1126 times
these are the vertical lines , BTW how many words are required in a post to not get it deleted and why delete peoples posts any way ?

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andrew
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by andrew » Mon Feb 05, 2018 3:53 pm

solo wrote:BTW how many words are required in a post to not get it deleted and why delete peoples posts any way ?
Not sure what happened to your post but there is no such word limit and your posts should never be deleted (unless they contain spam or other inappropriate content).

solo
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by solo » Mon Feb 05, 2018 9:13 pm

A pop up read your post has been deleted due to insufficient characters ..............................................................................................................................................................

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Husky
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by Husky » Mon Feb 05, 2018 11:19 pm

solo wrote:... and your latitudinal lines are just straight horizontal lines
Sure - till now I have no other information.
solo wrote:I need elliptical "Horizontal" lines in tapered pairs.
Why? Looks like your example globe is straight up under 90 degrees. Not tilted in any way.
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solo
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by solo » Tue Feb 06, 2018 1:23 am

It looks more 3D that way , they wrap around the globe and taper off into the distance .

solo
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by solo » Tue Feb 06, 2018 1:26 am

Like in this globe
2018-02-05_18-25-14.png
2018-02-05_18-25-14.png (34.15 KiB) Viewed 1109 times

solo
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by solo » Tue Feb 06, 2018 1:27 am

only with tapering

solo
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by solo » Tue Feb 06, 2018 1:31 am

Maybe it needs arcs like the longitudinal lines not sure I should do it both ways to see .

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Husky
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by Husky » Tue Feb 06, 2018 5:26 am

solo wrote:Like in this globe
2018-02-05_18-25-14.png
2018-02-05_18-25-14.png (34.15 KiB) Viewed 1103 times
solo wrote:It looks more 3D that way , they wrap around the globe and taper off into the distance .
Ok, understood. Unfortunately this image is plain wrong. Somebody tried to bend a 2D image into a 3D perspective image with just adding a few curved lines. That is not how perspective works and is not the purpose of a CAD Program.
Why is this image wrong?
If you see the latitudinal lines like those are drawn in the image the information is given that the globe is tilted. But it isn't. You can see that the center of the north pole and the center of the south pole is direct on the top and bottom of the perimeter circle of the globe = not tilted.

If you still like to accomplish this task with QCAD then I recommend to design a perspective globe slightly tilted. I think the real world axial tilt for our globe is somewhat around 23 degrees. I still think that a spline would work best for the latitudinal lines but one step at a time ...
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lphilpot
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Re: how do I draw tapering latitudinal lines on a globe ?

Post by lphilpot » Tue Feb 06, 2018 6:06 am

As a QCAD newbie, I hesitate to even ask and possibly add to the confusion, but...

solo, are you referring to arcs whose thickness tapers off toward each end, as if they recede into the distance? In other words, where nearest to the eye, the arc appears X units thick but tapers to a fraction of X before it disappears (in perspective) around the 'virtual' sphere? Your vertical lines drawing appears (to me) to be an incomplete attempt to accomplish that, albeit in the other direction.

If so, that would imply variable thickness/width along the length of the arc. Unless QCAD can do this (I'm not aware of a direct method), you'll have to manually draw each one from two or more arcs, trim appropriately and hatch between them. Otherwise, if you're looking for that kind of realistic rendering, a program such as Inkscape might be a better bet. You could possibly create the basic geometry in QCAD and import it into Inkscape via SVG (?), but rendering objects in 'viewpoint-perspective-accurate' 3-D is a bit beyond the scope of a 2-D CAD program.

But, if I'm misunderstanding your question, please ignore my interruption. :wink:
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