One problem perhaps eternal for the beginners: how to create and annotate an image like this one. The image contains hidden lines specific to a 3D body represented in the plan. If the software is easy to use, and possibly free, the better.
Well that image isn't very hard to draw*. But that seems to me a bit premature. I would first start by answering following questions:
Would you know how to draw that by hand. If yes then use a vector drawing application. Like Inkscape or Illustrator, or even something like vectorpaint. This is not much beyond lesson 3 into isometric drawing.
Do you know how to use TEX? If so consider using something like TIX. Or consider pylab/Matlab/Mathematica/R/etc. Again not a big deal.
Maybe a cad application? But most likely you may need 2 apps.
What do you consider easy? I mean there is no application that can just magically do that image with no training whatsoever.
Where do you intend to use the image?
* I could do the same in illustrator in less than 10 minutes.
My option regarding the free software is pretty simple.
For a real 3D model Blender https://www.blender.org/
For the anotations Inkscape https://inkscape.org/
You also could use for example Sketchup* https://www.sketchup.com to generate a 3D model to be used as a reference, (and then manually drawn in Inkscape), but Blender have some options to export to SVG (2D vector format)
But I would use Blender on more complex scenes, and probably if you want some kind of diferent perspectives, or you have some crazy slicing on the model.
The specific Image as joojaa pointed out is pretty simple to do as an isometric image, so the cuts on the sphere for example are simple elipses. In that case, Inkscape alone will do.
- Sketchup aditionally has something called "Face Me" components. This would be handly for example to put some labels that stay in the 3D space when rotating and moving the camera arround. The problem is that you need to render as raster images, not vector. But if the images are small inclusive a screen capture would be a fast way to get them from screen.
A low cost and easy to use option = Use a freeware 3D CAD for the base drawing and add the annotations in a drawing program
Here is sample screenshots (=bitmaps) from Design Spark Mechanical. That program is a free version of SpaceClaim Engineer 3D modeler. DSM's professional usage is prohibited by disabling a carefully selected part of the functionality - for example the text annotations.
Drawing colored extras is left possible.
The pictures are bitmap screenshots (=BMP). From left to right:
- hidden line (=wireframe without removing hidden lines, which are shown a little lighter
- hidden line, but some parts are selected
- In Photoshop enhanced version; line widths are doubled and hidden lines are spliced by the eraser
Unfortunately the output is not a vector drawing, only a bitmap. But it's resolution is full computer screen. So, the screenshots are useful in vector drawing programs.
If you need the images as vectors, do not expect good automatic tracing results from Inkscape's Trace Bitmap or Illustrator's Live Trace. I have not found even nearly usable settings in Inkscape. In Illustrator the big arcs and long lines get traced quite well (trace only strokes), but the dense central part must be redrawn manually. See the result:
DesignSpark Mechanical does not allow to edit imported non-native 3D files. That's a part of the "no freeware for professional users" policy.
An easy way to get mathematical symbols is copying and pasting from an equation editor. I have relatively new MS Powerpoint. From there one can launch (by Insert an equation) MS Equation 3. It's not a high quality math typesetter, but usable in many cases. The equations can even be pasted as vector images to Adobe Illustrator. Unfortunately Inkscape ignores them.
MS Visio is much more capable drawing program than Powerpoint for technical illustrations. It also has MS Equation.
About Open Office:
It has everything to add rich annotations. But its user interface needs serious studies. It's so different when compared to Inkscape or Adobe's and Microsoft's stuff. For example tracing manually some curves is very difficult until one succeeds to forget, how the curves were drawn in Illustrator or Inkscape.