Cau, does anybody know the (best) way to add rivers to the fractal hills generated with using random midpoint displacement method? Have I use L-systems for it?How? thanks

You may find some clues at Pandromeda''s website. They have a river generator for their MojoWorld Generator product, which generates fractal terrains:

www.pandromeda.com

Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.

Something I''ve thought about a bit (and will hopefully eventually get round to doing one day in the not too distant future.)

1) Select the highest point (vertex) on the terrain ( or any high point you deem suitable ).
2) Displace away from the point a bit (so you''re not directly above the vertex), and find out which polygon you''re above.
3) Find the downslope (tangent) vector for this polygon.
4) Follow this direction until you hit another polygon and find the downslope on that polygon and change direction

and so on, until the slope vectors reach some threshold (e.g. where the''re close to being level.

This will give you a possible route for your river. A bit rough and ready perhaps, but subdividing the path and adding a bit of noise will make it a bit more realistic, and perhaps modifying the terrain along the course of the river, letting it cut into the landscape. Depends how complex you want to go, maybe taking into account the hardness of the terrain you''re crossing (is it granite or sandstone?). Could get quite complex, but complex isn''t always realistic.

At pandromeda i saw exactly what i want to do,but i didn''t find HOW(i don''t wanna be mojonaut).In their SDK are only *.h files,no *.cpp ...
paulc:When i want add rivers(river bed)then those paths must fulfil some conditions(for example they must result in the same point).i think it could be good way how to do it.

thank you for replies

A little bit off topic:
I created a program that generates and edits height maps, so you can add rivers, etc. manually.
The program is free, GPL, and can be found at: http://hme.sourceforge.net

Regarding the Pandromeda site...what you really need is the SIGGRAPH proceedings for Kent Musgrave''s presentation on fractal terrain. Kent is the founder and genious behind Pandromeda/MojoWorld. He studied with Mandelbrot. And in his presentation he goes into some real technical algorithm details. (Though he doesn''t give away everything.)

The general SIGGRAPH course title is "Simulating Nature: From Theory to Application". He''s presented in that course for the past few years. Do a search in google, or go to citeseer.com which is a GREAT place to search for technical articles of every sort. (Don''t ignore the cached PDF capability which stores versions of docs that aren''t at the original link location anymore.) If you have money, you could purchase a set of "course notes" from SIGGRAPH 2000-2002 (safe to say Kent would have presented his fractal work during those years) from www.acm.org. But the proceedings for a given year may set you back a $hundred or $two.

Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.

what you need is perlin noise and nothing else. Just do a search on it.

Anonymous,

Your answer is quite naive. First of all, while useful for some cases, Perlin noise cannot generate realistic looking terrain with interesting features in general. Second of all, AlexanderCZ was asking about how to add rivers to fractal terrain. Your approach certainly is not an approach to adding rivers. Please try to plan your replies to be more on-topic.

Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.

Graham is right,citeseer.com is great place,i found there VERY GOOD documents - eroded fractal terrains,thermal weathering.I hope that i will get right...
Raduprv:i will try it and then i will let you know.
thank you