The RenderToTexture Blueprint works by using a bare-bones GameMode setup. There is a companion asset called the RenderToTexture_Game which references the RenderToTexture_Pawn. The Pawn is a very basic blueprint that has a Camera Component set to orthographic and a few event graph nodes to setup the rendering console commands.
The basic setup for using the Render to Texture tools is as follows:
Create a new blank level.
Place a Player Start from the Modes panel, Basic category, at location 0,0,0. Make sure the rotation on the Player Start is set to 0,0,0.
In the Content Browser View Options, enable Show Engine Content.
Browse to Engine -> ArtTools -> RenderToTexture -> Blueprints in the Content Browser.
Place a RenderToTexture_LevelBP Blueprint at location 0,0,0 in the world
Click the World Settings button. The World Settings panel will open where the Details panel is docked (by default).
Assign the *enderToTexture_GameMode Blueprint (found in RenderToTexture/Blueprints/) as the GameMode in the World Settings
You must enable the ability to export buffer visualization targets in the editor. To do this, click the upper-left Down-Arrow button in the perspective viewport and select High Resolution Screenshot, then enable Include Buffer Visualization Targets.
Leave this window open! This window will move behind the editor and should not interfere. If you accidentally close the window, the buffer images will not render.
Leave the High Resolution Screenshot dialog open.
Adjust the New Window Size property in Editor -> Preferences -> Play to a size that is a power of 2. A size of 512x512 is suggested and will not affect the quality of the output images.
The setting to choose which type of basic function will be performed is located under the Default category:
Below this you will find categories that correspond to the values in the Render Type property.
The only Property category besides Default that is relevant to all functions is the Capture Settings category. This category enables you to select which buffer targets you wish to save. For most cases, Base Color and Normal are sufficient. To render out opacity masks the Decal Mask option works well.
The resolution multiplier will multiply the settings you entered into the New Window Size in the Editor Preferences. So if you entered 512x512, a multiplier of 2 would result in a 1024x1024 texture size. A multiplier of 4 would result in a 2048x2048 texture size. Depending on the desired results, you may want to render textures as high as 4096 or 8192 in order to down-sample them in Adobe Photoshop. In those cases, it is usually suggested that you add a post process volume and set the Anti Aliasing setting to "none" to get a more crisp result.
This method currently saves .bmp format images. It is currently necessary to open and resave as .tga using an image processing tool. In practice, that is not a big deal since in most cases you will want to render at a large res and down-sample using an image processing pass later.
Finally, you can add a light to the scene if you like, it has no effect on the visualization buffers that are rendered out.