mapping dry land under sea level

jeanro

Hi Global Mapper users,

thanks for accepting me in the forum.

I am using Global Mapper for a while and most of the time, I have found the answers to my questions on the forum or elsewhere. My actual GM version is 21.1.0.

But this time, I have a particular question for a particular situation: I have a DEM representing a coastal area. In this coastal area there is a former wetland which has been dried for farming. The particularity of this place is that it's under sea level. So, I would like it to stay dry as well as I want the sea to keep its water. My question is: how can I represent my map with water in the sea at the normal level and no water in my dry land, which is under sea level ? I know that it is eventually possible to define a polygon and apply a different positive water in it for moutainous lake for example, but this option does not allow the user to define a negative water level.

Any ideas ?

Thanks,

J.

CraigA

I have this problem too, but I note no solution provided. Do the staff at Global Mapper not have any idea how to deal with land below sea level?

bmg_mike

The fast water level display in GM just displays water at a fixed elevation, with no concern for flow. We do have a Water Rise tool until the Terrain Analysis that can do a full flow analysis and do something like raise water from an ocean polygon to simulate something like sea level rise or storm surge.

However, the flow analysis is a very compute intensive operation and not something that can be easily done in real-time like a simple water level plane surface display at a fixed height. We could perhaps add an option to the water level display to only do it within a certain area or something though, but if you already have the water polygon then you don't really need the water level display anyway.

To auto-generate a water level polygon, you can try using the Contour Generator tool and create a fixed area above and below 0 (or whatever water level you want). Then just delete the areas for below 0 that are actually on land and just render the water polygons that are truly water.

Thanks,

Mike

Global Mapper Guru