You can dimension sketch elements from any predefined reference point. When you start a new part the origin is defined as the intersection of the three planes. Your first sketch will be on one of the planes and you can dimension from the origin.
I believe what he means is there a way to enter, for example a line from co-ordinate:
X=1.2, Y=12, Z=4.4
X=10.8, Y=7.6, Z=0
kind of like entering co-ordinates in AutoCAD 2D, for those familiar
it sure would be nice if you could go into 3D sketch, then when entering your point click in the status bar (that's the bar along the bottom) where the co-ordinates are, and enter your co-ordinates
or some other simple method, but you can't
you can do it after the fact though, draw any line
then click on its end points and enter the parameters
Kind of ironic that such a fine 3D modeling program is so weak (cumbersome) at 3D sketching
Welcome to the Forum. You can place your sketch element and then enter coordinates in the Parameters box in the PropertyManager, but the sketch element still won't be fully defined (locked in) unless you click Fix under Add Relations after entering the coordinates. I never use this method and I would be surprised if anyone else does, but it is possible. I believe the method described by Hardie is better.
the OP asked how to direct enter co-ordinates, not dimension from an entity
what if your sketch is not on a predefined plane, and further, is not defined from one of them?
by adding a point to the line I demonstrated (two points) you now have the definition of a plane , or just start with three points, you do not need a plane to enter a line or points, you can enter them directly, using them to define a plane, and then enter your entities on that plane
yes, using the pre-defined planes "is better" if you can use them, but knowing how to define any point, line, and plane is basic geometry you will need to know how to accomplish in SolidWorks 3D sketching
I'm with the other, I think after the fact is about as close as you'll get.
Draw a line from the origin and drag the other end into a (-,-) co-ordinate.
Click on the line and type the desired co-ordinates in, in this case 25,25.
With some effort you may be able to create an exercise for your students, starting with a pre defined sketch, and have them follow along, line upon line, changing the x,y, and see if they get the proper end result..
Doing this online by placing dimensions result in the same thing.
Just have them dimension everything for the origin.
This also works for a 3d sketch BTW.