Ranking Elevation Software/Program

General talk
1

Hi OpenStreetMap Forum

I´m not really sure where to turn or who to ask. Do you know any map software/program that could automatically find the lowest point in a country and when you would like to find the second lowest, third lowest point and so on you could find it ? And on that same coin, a software that could find the highest point, second highest, third highest point etc ?

Would love to hear back from you with any suggestions you might have. :slight_smile:

Best Regards

Anders

2

You need a GIS programm + height data. This question isn’t related to OSM. I’d recommend to ask at http://gis.stackexchange.com/

3

Thank you 4rch , i´ll have look. I really appreciate the answer !

4

The problem also needs more careful definition. Given the fractal nature of real surfaces, once you have the highest point, the remaining ones wil be infinitessimally close to it.

Given that the data available is likely to be on a grid, the easiest algorithm is simply to scan the whole grid, updating the coordinates wheniver a higher point is found.

Of course, you could fit a two dimensional curve to the grid, in which case the maths gets a bit more interesting. You can probably speed things up, especially for finding subsequent peaks, by assuming a maxium slope on a scale of a few kilometres, and skipping areas that could never exceed the current maximum on that basis.

You probably also need to consider how the data was obtained, e.g. how well does it eliminate buildings (although buildings may not be a big problem for peaks).

5

Hi Hadw

How would it be done if we are talking about the lowest points ? A lot of the lowest points in a country seems to be where the sea starts or deepest lakes and rivers. I´m thinking more in turn of finding the lowest land area points. Thanks for your answer .

6

Pretty much the same,except that low is more common than high, so it may be less easy to exclude large areas from the search. Also you are more likely to have buildings or varyng water levels, so you need a clear understanding of how the measurements you are using were made.

7

Thanks Hadw