User:PieSchie
Contents |
Enhanced Mapping with DigiCam
Calculation of Distances
As I have no real access to the railway-stations rail-yard. It is very difficult to estimate locations of signals and switches. Therefore I took some geometrical help. As on some Digital cameras the focal length is well known and then sensor-size (the size of the projected image in the camera( is also well known following calculations are possible:
Calculating Distances with known Original-Size
I took the following Input-Values:
- Original Size of Object (Railway-gauge = 1435mm) om
- Horizontal Sensor-Size (22,2mm) = sm
- Real Focal Length of a image (eg. 108mm) (see below) = f
- Image-Size in pixel (3456px) = ip
- Image-Size of the object in Pixel (90px) = op
With these information a simple math-solution is possible to create in every spreadsheet-application:
- Object-Size on the sensor osm = sm * op / ip (22,2mm*92px/3456px)
- R = osm / om
- distance d in mm = f * R
Now anyone can say that the size of the sensor chip and this pixel-size of the object is very difficult to get. I agree with that, but getting a Pixel-Size of 88 to 92 Pixels the Distance of the example above varies between 223 and 233 meters.
Some Point-And-Shoot Cameras with an intergrated Photographic lens have a focal length given that equals the 35mm-format. For the real distance the real focal length is needed:
- real Focal Length = 35mm-format focal length * sensor-width in mm / 36mm
Calculating Distances from size-distance-change
Input-Values
- Object-Size in pixel from Distance 1 (s1) = l1
- Object-Size in pixel from Distance 2 (s2) = l2
- let there be s1 > s2 and so l1 < l2
- Changed distance in m (as precise as possible) s1-s2 = ds
With these information a simple math-solution is possible to create in every spreadsheet-application:
- size-difference in percent p = s2/s1 - 1
- s1 = ds / p
- s2 = ds+s1
Note: This only works with 2 pictures taken with the same focal length and the object well centered in each image.
Enhanced Mapping using a compass
Position, Distance, Bearing
Knowing an Object and its real Distance from the current location (e.g. with Photographic enhancement) it is posible to take a bearing with the compass and create the position in JOSM by using the measurement-tool in the status-bar. It is important to know the local magnetic declination to bear according to true north and not magnetic south.
cross-bearing a position
When there is no posibility to get a GPS-Position at an object like an electricity pylon in the middle of an acre it is possible to estimate the position through cross-bearing
Therefore three steps have to be done:
- mark current location A and note true bearing from A to Object
- mark current location B and note true bearing from B to Object
- Use JOSM and its measurement-tool and create a Way from A with the noted bearing A-Object and from B with the noted bearing B-Object.
The crossing of the two ways mark the Position of the Object. Optimal positions A and B are when the difference between A-Object and B-Object is aproximately 90°. For better Estimation more than 2 bearing-positions could be made.
