I have to compare geometries anywhere in the world; mainly between 65N and 40S but also in the Arctic latitudes. I need "commercial accuracy" - not military or navigational. For example does a line intersect with a polygon and - if so - so they intersect for 50 km rather than 55 km. I store the lat and lng of these geometries.
Can anyone please tell me how to select the most suitable cartesian projection (from spatial_ref_sys) to transform the coordinates into before compare any line with any polygon ?
I have tried to use the lng of the centre of the line to select one of the SRIDs between 32601-32660 and 32701-32760. As many of you will know, these are based on the equator every 6 degrees and the 601-660 are for northern hemisphere while the 701-760 are for the southern hemisphere.
To test whether this works, I check whether the ST_Intersects() function detects that a point in Asia at 36.9417, 75.4083 intersects with a polygon of Asia after both are transformed with SRID 32643 whose central_meridian is 75 degrees. Sadly the ST_Intersects() function doesn't detect that the point is right in the middle of Asia, but when I use SRID 32644 whose central_meridian is 81 degrees, ST_Intersects() function detects an intersection between point and polygon.
There are many other examples of my "calculated" SRID being the wrong one. Maybe I'm overcomplicating ? I originally used SRID 4326 anywhere worldwide before testing with ST_Intersects(), and things seem fairly accurate except in high northern latitudes, so I was hoping to minimize inaccuracies by using different cartesian SRIDs at different longitudes.
Perhaps I need to find SRIDs which centre on the latitude of the geometries - not just the longitude ? Maybe I'm overcomplicating ?
Many thanks for your initial welcoming response. I hope that gives good information.