Details
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Type:
Task
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Status: Closed
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Priority:
Major
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Resolution: Won't Fix
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Fix Version/s: None
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Component/s: None
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Description
opengis is very nice, but we don't have a CIRCLE (ok it's mercator and blablabla), maybe we could use a circle->polygon converter.... example:
polygonfromtext("CIRCLE(10 20 30)")
could return a circle with radius 10, center point(20,30)
we could add a variable (a variable that should be placed in query cache flags or a global variable that should be used in replications) @@opengis_circle_points=360
we will do something like... (cos and sin are degree not radian)
for(i=0;i<360;i+=360/@@opengis_circle_points)
poligon point to (x=center+cos(i)*radius, y=center+sin(i)*radius)
poligon point to (x=center+cos(360)*radius, y=center+sin(360)*radius)
with this we create a poligon in each circle point
it's a nice feature since many code is done at client side and we could put it in server side
this function could return something like:
polygon(x0 y0, x1 y1, x2 y2 ... x360 y360) where 0=0degree,1=1degree..360=360degree)
i didn't read the mariadb gis source yet, but i think it's a easy function
we will not save circle, just polygons
javascript (using gmaps)
function drawCircle(lng,lat,kmRadius) {
var Cradius = 1; // km radius
var Ccolor = '#0000ff'; // color blue
var Cwidth = 3; // width pixels
var d2r = Math.PI/180; // degrees to radians
var r2d = 180/Math.PI; // radians to degrees
var Clat = (kmRadius/6378.8)*r2d; // using 6378.8 as earth's radius
var Clng = Clat/Math.cos(lat*d2r);
var Cpoints = [];
var i, theta, Cx, Cy;
var npoints=33;
for (i=0; i < npoints; i++){
theta = Math.PI * (i/Math.floor(npoints/2));
Cx = lng + (Clng * Math.cos(theta));
Cy = lat + (Clat * Math.sin(theta));
Cpoints.push(new GLatLng(Cy,Cx));
}
map.addOverlay(new GPolyline(Cpoints,Ccolor,Cwidth));
}
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ST_BUFFER(POINT(10,20), 30) returns just the polygon-from-circle centered in the POINT.
Example:
SELECT ASWKT(GEOMFROMTEXT("CIRCLE(10 10 20)"))
should return something like:
POLYGON((x0 y0),(x1 y1),(x2 y2), ... ,(x0 y0))
at spatial.cc (mariadb 10.0.3 - line 181)
Geometry *Geometry::create_from_wkt(Geometry_buffer *buffer,
Gis_read_stream *trs, String *wkt,
bool init_stream)
{
LEX_STRING name;
Class_info *ci;
char next_sym;
if (trs->get_next_word(&name))
{ trs->set_error_msg("Geometry name expected"); return NULL; }if (!(ci= find_class(name.str, name.length)) ||
wkt->reserve(1 + 4, 512))
return NULL;
>===< here we could put the circle feature and rewrite the WKT, or maybe create a new class just to circle and save it as polygon
Geometry *result= (*ci->m_create_func)(buffer->data);