UMS/InterpolationTutorial

Unreal Movie Studio Advanced Tutorial

by Hugh Macdonald

[UnFramed Productions]

Main UMS Page

Introduction

This tutorial aims to give you the understanding of how interpolation points work, and how to set them up

How Interpolation Points work

1. Interpolation is a way of getting a smooth path (in this case for a camera) from a series of points. It is not the same as splining, as I will explain.
2. A spline is a smoothed line that goes through all of the points in the path. This is commonly used for smooth paths, but not in Unreal.
3. An interpolated curve doesn't actually touch the points at all. It is pulled towards the points, but without actually going through them. This is the way Unreal uses Interpolation Points.

Adding Interpolation Points to your map

1. InterpolationPoints (hereafter called IP's) can be found under Keypoint >> InterpolationPoint in the Actor Classes Browser. The first thing to do is to add one to your level where you want the camera to start.
2. It will have an arrow on, and can either be rotated in the 2D views, or in the InterpolationPoint Properties → Movement → Rotation. This will define (funnily enough) the direction that the camera will be pointing.
3. In InterpolationPoint Properties → InterpolationPoint → Position, you should put the number that defines what point in the path this IP is at. This should start at 0, and I have been informed that the upper limit is 127 (thanks to TheMapper for that).
4. I think the best thing to do, is to first add the IP's to your level, in aproximately the right places. Then you can get the path set up correctly, before changing the speed.
5. Once you have got all your IP's in, there are two more that you have to put in. At the last point, you need to have two IP's. Then, put another one in the same position as the first, and give it the next Position after the last one. This is because IP paths actually loop, and the only way to get the path to go through a point is to put two IP's on top of each other. The reason the highest number IP is at the beginning of the path is because the camera will start half way between the first and last IP's.

Making your camera follow your Interpolation Point path

1. Once you have youe IP path in, select all the IP's (right click on one, and select Select all InterpolationPoint actors). Change the tag on all of them to the same thing. This could be something like CamPath1.
2. Now, in your Director, put the following two lines: Camera Camera1 CutTo and Camera Camera1 Interpolate CamPath1
3. You will need to make sure that you have a camera called Camera1 somewhere in the level. I would recommend that it can't see anything before it goes to the IP path.

Tweaking your Interpolation Point path

1. Now, if you followed my instructions for the Director in the first tutorial, you should have ChangeHUD and SetSpeed at the beginning. Change the ScriptVals on the command with SetSpeed in to 0.2. This will make the whole thing go in slow motion, which makes it much easier to write down stuff as you watch it.
2. Now, run the scene. Watch the camera go round the IP path, and write down something that will remind you every time the camera goes somewhere you don't want it to, either through a wall, or just out of line. If this is your first time using IP's, then you will find that you will probably have quite a lot of dodgy points.
3. Back in UnrealEd, find the offending points, and try to tweak them. There is not much I can do to tell you what to do here, as it is really just trial and error.

Setting the speed of the Interpolation Points

1. Once you have your path correct, you may want to play around with the speed. You will find that it looks a lot nicer if the speed does vary. Knowing when to vary the speed isn't something that I can teach you.
2. To change the speed, go to InterpolationPoint Properties → InterpolationPoint → RateModifier. Again, it is a matter of trial and error to find a series of values which you like. On each IP, the rate will be at that point, and it will change between the two points. If you want to change the rate very quickly, have two IPs very close to each other with different rate values
3. You can, if you want, change the speed of the game with the GameSpeedModifier, but this works seperately from SetSpeed. If you do use GameSpeedModifier, then make sure that it is reset back to 1 for the end of the IP path.
4. That is about it for Interpolation Points. Again, if you have any questions, do e-mail me at hugh@unframed.org.

What's next

In the [next tutorial]?, I will cover setting up effects, like explosions and breaking glass. This is the sort of thing that, if you have used UnrealEd extensively before, you will already know about

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Tarquin: Hugh, I've taken the liberty of copying the section on IPs in general to InterpolationPoint.

Tarquin: It's moved again to Making An Interpolation Path. Hugh, I suggest we move anything on creating the path to that page & point to it here.