photogrammetry

i do not really know how this works but hi I am Philemon. for a school assignment I need to program a app I have 2 years for this and it is for people that are interested in coding. I want to make a iOS app that can make 3d models from pictures (photogrammetry) and I know that there are already apps for this but I want to code this myself. I have a little bit of experience coding c# in unity but I really don't know where to start can someone help me? and I know that apple has reality kit but I want that people without a LiDAR Scanner can use this too. so where do I start witch language do I need to learn? every comment is welcome!!! kind regards Philemon