Thank you for contacting support. We can create a Mesh from scratch, assign this Mesh to the node of a new 3D scene, and then finally save a 3D scene in the STL format. Please refer to this help topic: Create a 3D Cube Mesh and Scene
In addition to the above reply, we have created a small project to generate a height map from the grayscale image. Please refer to this download link: HeightmapZip. Furthermore, we have logged a feature request to achieve this with a short API. We will include this feature in the next Aspose.3D for .NET API version 17.7.