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I'm currently using Inkscape to make some sketches as reference frames and simple drawings regarding space and orbital dynamics. But I've some difficulties when I have to draw an ellipse, its focus and its other geometric characteristics (I mean to individuate the focus by mathematic point of view). I don't know if in Inkscape I can draw an ellipse by assigning its geometrical characteristics as semimajor axis, focus, eccentricity and so on.

Can you tell me if Inkscape is able to perform this task or it is better to use other software? In addition to this, can you also tell me if Inkscape is good for drawings like these sample images? (Taken from some Space Dynamics books).

Can you point me to other software or online tools?

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    For complex shapes such as the exploded view of a rocket I will certainly create the CAD (or download it: you can find many on internet) then use a software like SolidWorks composer to create exploded view, export them into SVG, then import them into Inkscape for further modifications.
    – s.ouchene
    Commented Mar 23, 2022 at 9:53
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    Do you need mathematical accuracy? If so, then it's probably not as useful as some CAD software. I'd look elsewhere if that's the case. If not, then you can basically draw anything you want manually.
    – Billy Kerr
    Commented Mar 23, 2022 at 13:10

2 Answers 2

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You can continue in Inkscape. But the drawings of 3D models of the space rockets like fig 7_29 must be constructed in a proper 3D CAD software or they must be purchased. I skip that subject, because simple 3D programs generally do not generate exploded views nor export them as 2D vector drawing with perspective. You need a pro level 3D CAD program or at least something complex like Blender.

Ellipse problem

Construct the wanted ellipse so that you start from the focal points. In addition you must also define one point of the curve. In this example I take the extra point from the line which goes through the focal points.

Draw a horizontal line AB - It's 2 clicks with the Bezier tool (="the pen"). After the 1st click hold the Ctrl key to get it horizontal. The focal points are A and B. Draw a new horizontal line BC (green) to the wanted rightmost point of the forthcoming ellipse. Duplicate (=Ctrl+D) line BC and move the duplicate (red) starting from C to right. You need it for help soon. The right end of the duplicate is named to D.

Distance AD is one of the original geometric parameters of the ellipse. It's the sum of of the distances from a point to the focal points.

Have all point snaps ON for easy snapping, also snap to midpoints and to rotation centers.

enter image description here

Draw 2 different radius circles to A and D. Scale the rightmost circle so that it has one common point with the leftmost circle. Hold Ctrl+Shift for symmetric drawing and scaling from the center. The scaling snaps.

enter image description here

Move the rightmost circle to the focal point B.

enter image description here

Now you have got 3 points of your ellipse. You need 2 more. You get them by duplicating the circles and swapping the places of the duplicates (black)

enter image description here

Click with the Bezier tool a 5 point path (blue) through the crossings of the circles and C. It will be the marker path for path effect which draws the ellipse.

enter image description here

Insert path effect Ellipse by 5 points:

enter image description here.

Make the ellipse free for edits by applying Path > Object to path. Group it with line AB to keep the focal poins hanging around. You can make the line invisible in the Objects panel.

Effects of transformations: You may want to rotate and scale the group. The focal points are still OK after those transformations. Non-symmetric scaling and skewing the group makes the focal points wrong, but they are still OK if you consider the result as projection image of the straight on the face group.

Web service Geogebra allows you to draw directly an ellipse with given focal points. The image can be exported. As well you can define curves as equations. Check how useful the service is for your purposes.

ADD: A little thinking of your problem made clear that you probably have already drawn a good ellipse for your illustration Now you want to find its focal points. That's also possible in Inkscape with no numerical calculations. It's better to rotate a copy of the ellipse so that the major axis is horizontal. You can rotate it back after the focal points are found.

Drag a horizontal guide to the midpoint of the ellipse and rotate. To make it snap now and in the next steps have all point snaps ON, also snap to centers and rotation pivot points:

enter image description here

In the right the ellipse is rotated. The equation is the common relation between the half-axles (A, B) of the ellipse and the distance C from the midpoint to the focal point. It comes from the original definition of the ellipse and it's presented in elementary analytic geometry textbooks. One derives it with the Pythagorean theorem.

You want to find C when A and B can be found from the given ellipse. It can be drawn with a rectangular triangle:

enter image description here

The crossing of the blue and red circles is the wanted vertice of 90 degrees angle. One draws C (=black) from it to the rightmost point of the ellipse.

In the right the black line is rotated to horizontal with the guide, duplicated and the copies are placed to the right and left from the midpoint. The focal points are the endpoints of the black line.

DONE.

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    For 3D drawings (including exploded views), one can draw over a photo in Inkscape. The result won't be perfectly accurate in dimensions, but it's an easy way to get nice looking illustrations.
    – jpa
    Commented Mar 23, 2022 at 14:42
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    Good detailed photos of parts of rockets and space stations are not especially common. NASA has published some but I am not the right man to claim anything of their usefulness for the wanted purpose, licencing nor accuracy. A drawn copy of a photo is a coy of that photo. One cannot draw more than the photo shows nor isn't allowed to use it more freely than the license of the photo allows.
    – user82991
    Commented Mar 23, 2022 at 15:11
  • Most proper CAD applications do indeed export perspective images as vector drawinsg (atleast Creo, Solidworks, Catia and AutoCad do, probably NX too) most DCC apps also do this (or atleast Maya, Max and Blender do)
    – joojaa
    Commented Mar 23, 2022 at 21:07
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While its true you can use inkscape for this. Its not impossible after all any line drawing is possible to do in inkscape. though inkscape is not doing you many favors

Of your examples 2 were clearly made with something like tikz, one is made with a graphing application akin to matlab (but could be matplotlib or R too). Others are ambigious bout could be abything.

In reality i would consider something that answers the word dynamics. Personally i would probably use Mathematica. But you could try any number of constraint based tools (like CAD applications, geogebra, solvespace not sure it does ellipses, autocad solidworks etc). Graphing tools, tikz etc.

Benefit of above is that many of them can work in 3D so its easier to work in them. And they usually animate too.

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  • Inkscape is useful after plotting with such tools (I'd use python/matplotlib personally; TikZ has a pretty steep learning curve even if you already use LaTeX) . For example you can replace graph markers with icons, and add annotation and decoration
    – Chris H
    Commented Mar 23, 2022 at 15:20
  • @ChrisH maybe, i dont really remember what it was like when i didnt know how to use it. I mean i write postscript by hand all the time too and dont feel its in anyway complicated. So i will have to take your word on it. A lot of my peers and students also tells you inkscape has a steep learning curve too. And i know people who claim tikz is easier and others who claim the other way around. So i am unable tell anything about the learning curve steepness. But if you know nothing everything is hard i suppose. All i know inkscape isnt ideal for postscript or pdf roundtrips.
    – joojaa
    Commented Mar 23, 2022 at 16:18
  • I haven't tried postscript in Inkscape myself, and you're right: I've heard things about its learning curve too but I was lucky to not be under too much pressure. I suspect a strong coder might do more (up to all) in TikZ, someone more visual in Inkscape. Both are tools I use among others (including CAD), and all users need to strike a balance with what tools they use for what. Inkscape tends to be my finishing tool for posters etc. BTW you got a +1 (mainly for giving some appropriate tools for the job)
    – Chris H
    Commented Mar 23, 2022 at 17:20

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