coordinate systemcoordinates
I have some coordinates from an old Oracle database (AMANDA) and I don't recognize the format.
For example, converting these coordinates: 3109020, 10114224
Should result in a point near latitude, longitude: 30.195855, -97.756467
Does anyone recognize this format and how to convert to lat/lon?
EPSG:24378 Kalianpur 1975 / India I should be the local CRS in the region you mentioned. The extent seems to fit to that:
To get this picture using QGIS, create these text files:
E N
73.4775 34.3629
and
Easting Northing
3250193.00 1115573.00
3249214.00 1111220.00
Load each into QGIS as Delimited Text File, with blank as delimiter and setting CRS to EPSG:4326 for the first and EPSG:24378 for the second. Project CRS is EPSG:3857 to add Openstreetmap background with the openlayers plugin.
If the data is older than 1975, you might as well look for Kalianpur 1962 or Kalianpur 1880.
You can use GDAL cs2cs or ogr2ogr to reproject the data to any other CRS. For Google Maps, EPSG.4326 would be best.
Assuming you know AB, AC, and BC, then the answer is yes. It requires trigonometry. The following assumes a flat plane and that points A anb B are not on the same line of latitude or longitude. To get the lat/long of C you need to figure out the ΔX and ΔY from a known point (let's use A).
You're going to need the value of the angle θ, which is 90-a-λ
Let ΔXB and ΔYB be the lat/long difference from A to B (both of which have known coordinates). From basic trigonometry we know that sin(λ) = ΔYB/AB. Therefore λ = arcsin(ΔYB/AB).
By the Law of Cosines cos(a) = (AB²+AC²-BC²)/(2*AB*AC), which means a = arccos((AB²+AC²-BC²)/(2×AB×AC))
Therefore θ = 90 - arccos((AB²+AC²-BC²)/(2×AB×AC)) - arcsin(ΔYB/AB)
With θ calculated, we're back to basic trigonometry again: sin(θ)= ΔX/AC and cos(θ) = ΔY/AC. Therefore ΔX = sin(θ)×AC and ΔY = cos(θ)×AC. Just add those values to the coordinates of A, and you have your answer.
TLDR version:
Best Answer
That looks like a projected Coordinate System, with units in either feet or meters.
You can figure out what coordinate system your points are in by trying out different coordinate conversions on this website.
Enter the lat/long of a coordinate, choose the target CRS, and click convert. Try out different target CRS's until the conversion gives you the known coordinates.
Given the location, start by testing CRS's with Texas in their name, eg:
It shouldn't take long to test all 10 Texas-specific CRS's. If none of them work, expand the search to US-specific CRS's, and North American-specific CRS's.
Remember that the US often uses US survey feet or (international) feet for the unit of measure. When you see large numbers like that, check the foot-based coordinate reference systems first. Austin falls into the Texas Central zone in the State Plane Coordinate System, maybe try that one first. You will find it difficult to determine which geographic CRS is being used. It's probably one of the NAD 83 ones, but there have been several re-adjustments and coordinate differ at the centimeter to decimeter-level.
An alternate approach is to figure out where the origin of the CRS is. Then you can limit your search to CRS's with that origin. Find the origin by measuring from the known point, 3109020 units to the west and 10114224 to the south. Since the data is in the US, you'll have to test it with both meters and feet. If the origin is on the equator you're probably looking at a UTM projection.