The Triplanar Map node and the Triplanar projection node are being used to map a Check texture and an imported texture to different projection planes of an object.
The Triplanar Projection node is used in conjunction with a Triplanar Map Node. It takes the coordinates in world or object space and will pick the projection axis depending on the active axis of the Triplanar Map Node. This gives a quick way to map a texture on any object and presents the possibility for texture transforms local to each projection axis. The Triplanar Map node has six input pins representing the positive and negative X, Y, and Z planes. The same or different texture nodes can be mapped to each of these input pins).
The Triplanar Map node and the Triplanar projection node are being used to map a Check texture and an imported texture to different projection planes of an object.
This texture is used for mapping the samples of multiple textures along three planes, x, y and z in world space or object space coordinates and blending them to create one seamless texture. In most cases and depending on the complexity of the model, it generally allow users to map textures without necessarily having a UV-mapped mesh.
The Triplanar Map Node divides a material map into six areas corresponding to the x,-x,y,-y,z and -z axis. Initially, a texture would cover the entire surface of the object but the triplanar mapping confines visibility of the texture map onto the corresponding axes that are active for that texture. The illustration below shows a comparison of an image without the triplanar mapping versus one that is plugged into the Positive X and Positive Y axis pins of a Triplanar Map Node:
The Triplanar Map Node may further depend on a Triplanar Projection Node which localizes the projection of the texture to a corresponding plane and allows texture UV transforms relative to that projection axis:
The Triplanar Texture has the blend angle and blend cube transform parameters which can be adjusted to soften the seams.