[GIS] Convert land-based camera image pixel x,y to ground lat/long or x,y,z

coordinate systemimagejava

I have a number of cameras at various known locations (x,y,z) and directions that are above ground about 20 feet pointed at different ground locations about 100 feet away from each camera, and whose furthest fields of view (FOV) are about 300 feet. None of the cameras are pointing directly N-S or E-W. Because of the relatively short distance, I don't need to take into consideration the curvature of the Earth.

I am detecting moving objects within the camera FOV and obtaining their image pixel x,y contours and centroids. How can I convert the pixel x,y locations into (initially 'flat') lat long coordinates or relative ground x,y locations? I am obtaining elevation data, so will be adding the ground height (z).

Am trying to do this in Java as much as possible, so any pointers (e.g., algorithms, code libraries, etc) are welcome

Best Answer

This is something I'm working on as well and I need to improve the accuracy of the run. One thing to do is use the opencv library. For instance in Python:

import numpy as np
import cv2
twoD = np.array([[   0.      ,    0.      ],
       [3840.      ,    0.      ],
       [3840.      , 3240.      ],
       [   0.      , 3240.      ]])
threeD = np.array([[-1.9292996 , 94.3841359 ],
       [-2.1339714 , 92.7364367 ],
       [-0.7249805 , 92.5754107 ],
       [-0.568487  , 94.2150297 ]])
pixelcoords = (1051.311157, 3167.13916, 1) # pixel coordinates
H = cv2.findHomography(twoD, threeD, cv2.RANSAC, 5.0)
latlon = H @ pixelcoords
latlon /= latlon[-1]
# latlon = np.array([-0.64319293, 93.78276724,  1.        ])

Related Solutions

[GIS] How to convert MGRS to Lat/Long or UTM

I had to write code to convert MGRS to LL last year, however I am unable to post the code. What I can post though are the two main resources I utilized while writing the code:

US Military Grid Reference System description, published by NGA and the related Appendix and an Online MGRS to LL Converter to check your results as you are coding.

edit: There is also GeographicLib, an open source library that has code for MGRS conversions, and is licensed under MIT. You'll need to look at the GeographicLib::MGRS class, and the MGRS.hpp and MGRS.cpp files if you need to look at the code.

edit #2: If you can elaborate more on whether you are looking for code, a library, or a utility to convert one or more coordinates, you'll get better answers.

[GIS] GeoToolKit conversion from lat/long to UTM

I figured it out. Here is the solution in case anyone else is interested. UTM is not a single projection, but actually a set of 120 different UTM zones. The zones are divided in 6 deg increments starting at -180 deg longitude, continuing to 180 deg longitude. This creates 60 zones, and since there is a northern and southern zone for each range, the total becomes 120.

Update: As mentioned below, this is a simplification of the UTM standard, and will not be accurate for a few unique regions around Norway.

The next hurdle is then converting the UTM zone to the EPSG database code, so it can be retrieved using the geotoolkit API. The code makes it clear how the EPSG code can be reached, once you've figured out the UTM zone.

private static int utm_zone( double _long ){
  assert _long > -180.0 && _long < 180.0;
  return (int)(Math.ceil((180 + _long)/6.0));
}

public void asUTMCoordinates( double longitude, double latitude) throws
     MismatchedDimensionException, TransformException {

  Point p = FactoryFinder.getPrimitiveFactory(null).createPoint( new double[] {longitude,latitude} );

  // define base EPSG code value of all UTM zones;
  int epsg_code = 32600;
  // add 100 for all zones in southern hemisphere
  if (this.getLatitudeInDeg() < 0) {
     epsg_code += 100;
  }
  // finally, add zone number to code
  final int zone = utm_zone( longitutde );
  epsg_code += zone;

  MathTransform crs_transform;
  try {
     CoordinateReferenceSystem wgs84  = DefaultGeographicCRS.WGS84; // EPSG:4326
     CoordinateReferenceSystem utm    = CRS.decode("EPSG:"+epsg_code);
     crs_transform = CRS.findMathTransform(wgs84,utm);
  } catch (NoSuchAuthorityCodeException e) {
     throw new RuntimeException(e);
  } catch (FactoryException e) {
     throw new RuntimeException(e);
  }
  DirectPosition p2 = crs_transform.transform( p.getDirectPosition(), null );
  double[] c = p2.getCoordinate();
  System.out.println( String.format("%d, %f, %f", zone, c[0], c[1]) );
}

Best Answer

Related Solutions

[GIS] How to convert MGRS to Lat/Long or UTM

[GIS] GeoToolKit conversion from lat/long to UTM

Related Question