Maps with sea floors as terrain?

[Wolverine@MSU]

Prompted by an inquiry from edbanger, I have been investigating the availability of bathymetry (ocean depth/terrain) data for making maps containing "below sea level" terrain. For instance, lets say sea level goes down (global cooling?).......what would the terrain be like? Turns out there are data sets available, covering most of the planet, and best of all, with a little data processing, they can be brought into Microdem and exported as a heightmap. I only have the dataset with 1 arc-minute resolution, but hope to retrieve and install the 30 arc-second dataset (equivalent resolution to GTOPO30 data).

Opens up a whole new region of the planet amenable to RT maps. I can envision a scenario where sea level is really low, and periodic "flooding" events gradually raise it.

[EPH]

I dimly remember a RRT2 game set in the US after the oceans rose. Don't remember anything about it except that the concept was cool.

[Hawk]

I remember that map too. It was one of Gwizz's brain-childs'. It was called Heartland Flood I believe.
It's not in the archive here but it is over at The Terminal.

I thought you couldn't do that in RT3?

[Gwizz]

With all the talent on this board, I won't be surprised to hear someone found a solution.

[Wolverine@MSU]

I was able to obtain the 30 arc-second data set (equivalent to GTOPO30). The coordinate files get to be pretty big, so there may be some limit to the size of a region I can turn into a DEM for use in MicroDem. For instance, a region covering 5 degrees of latitude and 11 degrees of longitude generates an XYZ file that's 18 Mb in size. I don't know if Excel will handle a file of this size for converting negative elevations to positive ones. I may have to write a Quickbasic program to do the conversion, but Microdem is able to handle the unconverted file and create a DEM from it. Problem is that anything below 0 meters is set to 0 meters because of the heightmap elevation database. Maybe the best way is to customize the heightmap database for each map to match the specific dataset. I'll keep you all updated. I can entertain a limited number of requests for these unique heightmaps.

[edbangor]

THanks for all the help with my idea - which is for a TM map BTW - and for Wolverine for coming up with a solution which I'm going to test out in a minute.

The idea is to have the English Channel drained (for some reason) and then populated. Naturally they'll need a rail network, to compete with the British and French companies on either side as well as the Chunnel running through the middle (now on the surface or perhaps under a ridge running across if that's possible?).

What I wanted was to have the sea bed lower than the land, to create an 'issue' of getting tracks up onto the land more of a challange.

[brunom]

Might sound very basic, but you know that in Microdem you can set max and min elevation and that that can have negative values, right?

If you change the height colouring to grayscale, the scale is defined based on the min and max, which can be default, equal to min and max of the map, or any set of values...

Reach this panel through menu -> modify -> elevation
There are options for bathymetry as well, so it looks like the program can handle what you need.

if not, at least it seemed like a valid idea to me..

B

[Wolverine@MSU]

I've seen that but haven't had a chance to try it yet. The problem with grayscale maps is that you are limited to only 256 levels of elevation, whereas with the 'ELEV_COLORS_0-9999.dbf" you get 1000 levels of elevation. I havent tried making a bigger DBF file yet, but have figured out how to rescale the 0-9999 DBF to cover any given range of elevations.

[EPH]

Geologically, both the Mediterranean and Black Seas have been cut off and (mostly) drained.

[brunom]

Will a map in RRT3 really need 1000 different heights instead of 256...

"Geologically" the Great Lakes could be drained too - that's another idea for a map/scenario...

I don't think the Black Sea was ever a dry sea bed, EPH. It was irrigated plains, which got flooded after the Mediterranean waters managed to pass the Bosphorus hills (now bosphorus straight)..

[Wolverine@MSU]

Will a map in RRT3 really need 1000 different heights instead of 256...

I don't know the answer to that one. I haven't made a direct comparison in what an imported map looks like under each condition. Looks like an experiment is in order.

"Geologically" the Great Lakes could be drained too - that's another idea for a map/scenario...

I already looked into this (being from the "Great Lakes" state). Unfortunately, the data set from GEBCO (http://www.gebco.net/) does not contain bathymetry data from the Great Lakes, although the data are probably available from somewhere.

[Gumboots]

Wolverine, did you ever look into how difficult to would be to raise sea level on a DEM dataset? I imagine that in principle it's easy enough (you'd just deduct the desired rise from the present elevations) but I'm wondering how hard it would be in practice if you wanted to get a finished .gmp out of the process.

[Wolverine@MSU]

Wolverine, did you ever look into how difficult to would be to raise sea level on a DEM dataset? I imagine that in principle it's easy enough (you'd just deduct the desired rise from the present elevations) but I'm wondering how hard it would be in practice if you wanted to get a finished .gmp out of the process.

Probably not that hard if one had some knowledge of manipulating the .dbf file used in Microdem to assign colors to elevations. All you would need to do is shift the entire color table values down, so that the color assigned to elevation "X" was now assigned to elevation "X + sea-level increase" and then filling in the elevations between "0" and the new sea level with RGB values of 255,0,0 (RED). That would be an interesting project to see how it would work. Of course the easier way is to use the Editor to "Paint" a new sea level by using the "Fill below" option of the paintbrush.

[Gumboots]

Well yes you can paint it on, but that won't do anything for the actual level of the terrain. Your blue paint will be going uphill and that is going to look mighty weird in some places.

IMO it'd have to be done properly by changing the colour assigned to each pixel. That would give an immediately useful and accurate result when imported into the RT3 editor.

Obviously you'd be wanting some sort of script to do the donkey work here, otherwise it'd take forever and you'd go mad in the process, but it should be possible.

What's the height resolution for each colour? Since it's called ELEV_COLORS_0-9999.dbf does that mean you get 10,000 levels at 1 metre intervals?

[Hawk]

Well yes you can paint it on, but that won't do anything for the actual level of the terrain. Your blue paint will be going uphill and that is going to look mighty weird in some places.

I'm pretty sure you can change the elevation when painting oceans, IIRC.

[Gumboots]

Not with oceans as such, but you can do it with the lake tool instead. The problem is that you have to do every cell manually, as well as painting them. Much better if the heights are already sorted before importing the TGA.

[Hawk]

That's right. It's the lake and river tools you change elevation with, but I think with the lake tool you can select a greater range than just one cell, right?
And I believe even after using the lake tool to lower elevation, then painting in the ocean, it's still not the same color as the ocean is when done in the DEM.

[Wolverine@MSU]

Making the heightmap to contain sea-level data is definitely the way to go. That way when you import the heightmap it will automatically be designated as sea-level (0 elevation) and have a uniform paint applied. It's pretty easy to do this, as stated above, by modifying the .dbf file used in Microdem to shift the color table down and filling in above with RGB values of (255,0,0). I tried it with a grayscale map by repainting the gray levels up to a certain value with red, but the result was escarpments all around the shores because the grayscale goes from sea-level (black or red) to the value of the elevation within a few pixels.

Here's an example of Central/South America with sea-level raised by 1000 meters in Microdem and imported into RT3

[OilCan]

That would be an interesting project to see how it would work. Of course the easier way is to use the Editor to "Paint" a new sea level by using the "Fill below" option of the paintbrush.

Actually, this is the easiest way to raise sea level. It is fun to do in the editor. Use lake height tool and fill (bucket) tool set to BELOW. The sea rises as you glide the marker inland from the ocean. Don't hold down control key - this allows inland depressions to fill only when the sea reaches them.

[Wolverine@MSU]

The only problem with that method is that the color under the newly created water is not changed to the blue that is under the original water. It's easy enough though to use the color-picker to select the right color blue and paint it manually.