geogem

Basic spatial functions - bit of a learning for myself

Simple start to a spatial library in Ruby to practice my coding and learn some maths.

Wanted to make some simple spatial functions to calculate the distance between two points, find the area of a polygon etc. Just uses ruby and maths so far but might have to add in other libraries - proj4 most likely if I want to add in the ability to use multiple projection systems.

Only works in British national grid.

So far no conversion from or to geometries, the fucntions take in coordinates as strings using the WKT format - you can either add the brackets or without i.e. "x y,x y,x y"

The gem has been split into 2 seperate class objects Polygon and Point, with Polygon objects comprising of list of points. Both classes have a variety of functions that can be used to perform various gis functions.

Rspecs are in place to ensure the functions work for basic cases. More detailed test will need to be conducted to further devlop the functions and ensure all special cases work correctly i.e. insection of 2 parallel lines might casue it error.

1. distance - the distance between two points - using Euclidean distance.
2. point_buffer- creates a circle - takes in a point, the radius and the distance between each node - smoothness of circle - must be >0 smaller number means less nodes and less detail returned
3. centre_point - feed in polygon and returns its centre point
4. bound_box- feed in site and this will return the min and the max of the polygon
5. Generalization - both radial thinning, perpendicular distance and douglas Puecker
6. to_wkt - returns the class object nodes as a wkt
7. Area - will return the area of the polygon
8. intersects? - returns true if the 2 polygons intersect with each other or 1 polygon sites on top of the other
9. Dissolve - Takes 2 intersecting polygons and returns a single larger polygon
10. cleaner - Removes self-intersections from a polygon

To do:

1. refactor- pretty dirty
2. BUffer lines
3. buffer polygons
4. clipping of polygons
5. Fix generalization algorithms (radil and perpendicular distance) both work but some strange behaviour
6. Validation - syntax errors of WKT, UK bounds check, etc

Function explination - because the code is getting very dirty!

to_wkt

Returns the polygon's nodes in Well Known Text format i.e. "x y, x y, x y". Nice and simple!

bbox

Returns 2 points in the form "x_min y_min, x_max y_max".

dissolve

Returns outline of 2 overlapping polyons. It first checks the 2 polygons are overlapping by calling the intersects? method. It then retrives the minimum of the 2 bounding boxes, it uses this point to calculate which point is closest to that point and therefore likey to be in the resultant outside edge. The lines of both polygons are then re-ordered to start at the point closest to the minium and if the polygons are in anti-clockwise they are reversed to be clockwise. The 2 lines are then passed to a switch method, which decides which line point to use next.

With minor sweaks such making 1 polygon clockwise and the other anti-clockwise this can be used to do clipping instead of joining or an inner join where only the over lapping parts are returned (although in it's current state that would only work for polygons where they had a single area of overlap)