However they are totally differently obtained features, with absolutely no relationgship whatsoever in the firmware. The only thing that '3D Building and Landmarks' and '3D Terrain' have in common is the '3D' in the descriptions. My layman's understanding:
- "3D Terrain" is DEM [Digital Elevation Modelling], a generic term applied to several methods of representing relative elevation on a screen or printed on paper. Garmin's DEM is done with colour shading to give the impression of hills and valleys etc., the visual effect being much like the printed colour shading in a child's school atlas. A much lower resolution scaled form of it is included in modern basemaps which show when zoomed out.
- "3D Buildings and Landmarks" are not '3D' in the sense that objects don't appear to project from the screen like a 3D movie or TV, rather they are a semi-transparent overlay constantly updated on a moving map and are best thought of as a moving sketch of the objects where our own brain supplies the sense of three-dimentional shape and depth perception in the exact same way as when we look at a perspective image drawn on paper. That constant redrawing and updating of the image does take a fair amount of processor power, sometimes to the detriment of other tasks causing a general 'slow-down' or lagging in the unit. The nuvi 7x5 is an older series which i've found sometimes struggles when using gmap3d.img navigating in a big city [Interestingly, it's the other way around. It hasn't got the ability in fw to display 3D Terrain]. Maybe the CPU power/clock speed in the nuvicam is quite borderline so Garmin dropped the feature. Or maybe as suggested they'll release an update model with 3D buildings in the firmware. One thing, afaik, writing it into the firmware at the time would have been no big effort as it would have been a simple 'pinch' from other existing fw. I'm not a programmer and perhaps that's a too simplistic view, but i don't think so. My conclusion is that it was left out on purpose, either for marketing purposes ongoing or because the unit might choke on it. Either way again 'Garmin is being so Garmin' by describing the nuvicam as a 'prestige model' imo or it's all just a bit of a con.