SRTM Seafloor

Hi All,

I’m starting to clean up some SRTM data and wondered if anyone had a method or macro for applying a gradient from 0 to the coast (which I managed to raise to 140m in Photoshop - see image). I tried putting a gradient mask around in Photoshop but the results weren’t very satisfactory. I’d like to try and get a reasonably realistic seafloor.

Edit: I realise I could erode but I don’t want to change the existing land form.



Combine a “constant” with the terrain, set combiner to “max” mode. Then set preview to the combiner, and then raise the constant height until the land is level at the beach. Next you can select this area using a “Height selector” on the original unmodified terrain (use height=0), and the use it as a mask when you combine the previous terrain with your “seafloor” terrain “inverted”, use the “subtract” mode in this combiner.

Thanks, that raises the flat seafloor to the level of the coast unless I’m missing something.

What I’m trying to do is a apply a gradient/slope from the coast level (140m) down to the current seafloor (0m) at a distance from the coast (500m?

Perhaps there is something I could do with blur and a mask.

You are indeed missing the next step. What I did here is to raise the floor to a natural level, so the transition is smooth, and then subtract an inverted seafloor terrain from that flat plane, which will scoop out the excess mass from the flat box, making it look realistically dipping. Then you can tweak that inverted seafloor terrain to your heart’s content non-destructively.

Thanks for getting back to me, I’ve only just had the chance to start looking at this again.

And sadly, I’m still not getting it. I can raise the seafloor from anwhere between 0 and 150m but I can’t get a slope.

I’ve uploaded a diagram and the project in the hope that you can help me.

Thanks in advance.


Could you also send me the input heightmap? You can pm me instead of posting here.