How to change values in a gridded matrix

I am struggling to change the values of a DEM (Dig. Elev. Map.) for a specific area limited by a polygon.

I have the following data: The grid coordinates X Y and the data Z(grided with griddata) and a polygon coordinates x y where i want to change the Z inside that polygon. I want to add elevation over a loop (its a tidal cycle) only inside that polygon. Currently i was trying to separate the interpolation into two separated areas, so i would griddata the area inside the polygon and the area outside separately (using inpolygon).

But this solution is not very elegant and it is time consuming. Also the final result is messy.

Another option is to repeat the inpolygon and griddata for every loop step, but this will consume a huge amount of time.

I wonder if there is something out there that would allow me to select the area inside a polygon for a grided matrix.

Thank you very much Rod

[Walter Roberson]

Is the grid equi-spaced? If so then you could poly2mask and use the mask.

[Coastal_Eng]

Hey Walter,

Great advise. Just solved the problem. Thank you so much !

Cheers