What are FreeCAD's coordinate systems?

in this video we're going to look at freecad's global and local coordinate systems stick around [Music] hi i'm jeff and i'm here to help you learn freecad so you can design the things that you've imagined if you're new here don't forget to hit the subscribe button so you can stay up to date with my videos freecad has two coordinate systems that work together but sometimes they seem a little bit strange i got asked a question about this a while ago and to be honest i bollocked up the answer so let's have a look at them freecad has a global coordinate system which defines the whole model it also has a local coordinate system which is based on the planes used in the part design workbench i'm going to give you an overview of the two coordinate systems and give you a demonstration of how you can use planes and the local coordinate system to override or adjust the attachment point of the plane if you'd like to support the channel you could buy me a coffee through the link in the description below now let's get started i'm using freecad version 0.19 for this demonstration and i'm running it on kubuntu linux version 20.04 lts as a general rule we don't use absolute coordinates in freecad we would normally design a part that was say a meter long 250mm wide and 50mm high rather than drawing a box starting at zero zero zero and going to one thousand comma zero zero et cetera et cetera it's just easier that way in a typical design session we would use both the global and the local coordinate systems without really paying too much attention to either of them freecad's global coordinate system is represented by a cube with its origin at the dead center of the cube typically speaking the x-axis moves left and right horizontally the z-axis moves up and down vertically and if i switch to isometric view you can see that the y-axis moves backwards and forwards in and out of the screen this coordinate system allows you to draw a line from any point to any point in 3d space assuming that your software supports it which as far as i can see freecad doesn't early on in my career i used a 3d cad system that did allow you to do that and whilst it gave you quite a bit of freedom it also made things a little bit more difficult and i think i prefer the pre-cad method of doing things where you work with objects not coordinate systems i'll concentrate mostly on freecad's part design workbench in this video precat's part design workbench uses a plane based system for defining geometry the planes are cartesian planes which we learned about at school they are a two-dimensional cartesian plane where the x-axis is horizontal and the y-axis is vertical the plane is anchored in 3-d space with an attachment point this may be confusing to some so let me step out of freecad for a moment and explain further one way to think about this is to consider a drawing on a piece of graph paper here's one i produced earlier as you can see it's just a simple sketch the origin point is about wall here and as i move it around my environment see the origin point moves but everything else stays relative to the origin point now consider this block of wood is the physical representation of that sketch origin point is still down here move that around again you can see that the origin point moves but everything else is relative to it this is how planes work in freecads part design workbench pre-cut has three basic planes but you can create other planes if you need them the three planes are the xy plane the xz plane and the yz plane each of these planes passes through the origin of the model i've recreated the paper example as a sketch to further explain how the planes work you can see that the sketch looks just like the one on the paper and if i extrude it out using the pad tool it will look like a block of wood the plane that i use to create the sketch passes through the origin of the model but what happens if i want to create a plane that doesn't pass through the origin well the easiest way to do that is to select a face on the existing model and then create a datum plane this creates a plane that is parallel to the original plane but is also offset from it so if i turn off the pad and turn on the origin should be able to see and rotate it that this is the original plane and this is the datum plane you see there are is an offset between them now when you select the datum plane and create a sketch on top of it you'll see that the items in the sketch are also offset from the original plane you need to be careful when you use this method because you run the risk of the topological naming problem raising its ugly head there is a link up above to my video which explains the topological naming problem now let's have a quick look at local coordinate systems before we try and move a plane in the global coordinate system using a local coordinate system as its name suggests a local coordinate system is specific to a feature in the model two examples of this are sketches and datum planes i'm going to use the datum plane that i created earlier just to illustrate the principles of the local coordinate system the local coordinate system works the same regardless of which plane or view that you're working with the x-coordinates are horizontal across the bottom of the datum plane and the y-coordinates are vertical up the screen the z-coordinates go in and out of the screen so it's much like using a piece of graph paper you can see this behavior whenever you are editing a sketch your sketch is in two dimensions you can place your sketch elements in the x and y coordinates but you can't change the z coordinates all geometry that you place in the sketch is relative to the sketches origin point or zero comma zero regardless of where the sketch actually lies within the 3d coordinate space precat automatically translates the coordinates in the sketch to the global coordinate system so that the model is created correctly after all that waffle let's have a look at how this actually works each feature in a freecad model has a placement point some features only have placement points but those features that are defined in the part design workbench also have an attachment point so if we have a look at this cube which was created in the part workbench you can see that in the data section it has a placement point which in this case is zero zero being the zero being the origin of the model itself if we click on the pad and then open the pad sketch you'll see that the sketch has a placement point and it also has an attachment point the placement point is the actual origin point of the feature in the 3d coordinate space the attachment point is the offset from the placement point in the global space of the plane in which the part design workbench feature was created now that's a bit of a mouthful so let's have a bit of a look at it so what i'm going to do is hide the cube turn on the pad get it to screen and then also turn on the datum plane now you can see as i said before in the sketch of the pad it's got an attachment point and a placement point and that's the same as with the datum plane now what i'm going to do is i'm going to adjust the attachment point of the datum plane so i can move it back or forward up or down left or right in the global coordinate space by changing the plane's local coordinates remember that the placement point is in the global space and the attachment point is in the local coordinate space also remembering that in the local coordinate space using this data and plane as an example the x and y coordinates increase and decrease along this axis at the bottom of the plane the y-coordinates increase or decrease along this axis in on the plane and the z-axis increases and decreases forwards and back of the plane so if i want to move the plane closer to me or forward in the model i click on the z coordinate in the attachment point and then i can simply move it forward or backwards when i do that anything attached to that plane will also go with it so if i turn on the sketch you'll see and then go back to the datum plane and manipulate the z coordinate and once i enter it you'll see the sketch followed as well so do it again so it leaves the sketch behind until such time as we confirm that that's where we want it and the sketch comes forward similarly if i push it backwards the sketch goes with it you might be saying to yourself hang on jeff the axis down the bottom here says that y is going in and out of the screen well that's because that is showing the global coordinate system not the local coordinate system it took me a little bit a while to wrap my head around that one because i kept doing dumb things getting back to it if i wanted to change move it up the screen i would manipulate the y coordinate as you can see here and the sketch follows similarly if i want to move it left or right i just manipulate the z x coordinate and it goes with it features created using the part workbench and the draft workbench are not attached to planes so they are called unattached features when you create a datum plane in the part design workbench you can either make it attached or unattached so let's have a look at that for a moment to demonstrate that i will create another datum plane and i will simply accept the default coordinates without attaching it to anything now when i have a look at the datum plane itself you can see that like the cube it only has a placement point which i can adjust in the global space but if i was to attach the datum plane to a surface on a feature you'll see that the datum plane has placement point and an attachment point this shows that it's an attached object now the only way you can change the placement of the datum plane is through its attachment point and this is where the local coordinate system comes into play in this particular instance because of the orientation of the plane the z-axis is vertical in the same way as the global coordinate system but if we have a look at the other datum plane activate that its local coordinate system is such that the z is going in and out of the screen like so it's really important that you understand the difference between the local and the coordinate system if you are planning on using planes and manipulating the location of the planes because once a plane is attached to an existing feature you need to change the attachment point in the local coordinate space but if you don't attach a plane to an existing feature you have to do it in the global coordinate space can do your head in a little bit as it did for me for a little while but now that i understand it it makes sense and i find that it works really well but your mileage may vary well i hope you enjoyed the video if you did please click the like button if you're new here subscribe to the channel and click the notification bell so you stay up to date with my videos i'm grateful for all the support that i've received on this channel and if you'd like to help me with my work please consider buying me a cup of coffee through the link in the description below thanks for watching and we'll see you in the next one

Channel: Glasson Design Studio

Views: 3,041

Keywords: freecad, freecad part design, freecad 19, part design, freecad 0.19, freecad part design workbench tutorial, freecad part design workbench, freecad 19 ubuntu, freecad part design tutorial, freecad 19 tutorial, freecad drawing, freecad tutorial, part design freecad tutorial, part design freecad, 3d modeling tutorial

Id: jJ9qviNaJkg

Length: 12min 47sec (767 seconds)

Published: Mon May 31 2021