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Last update:
04 01 2011
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Fast, flexible and accurate technology
Equipment

Helimap System SA uses only its own equipment, designed in-house and protected under the Helimap System® name. The system is an evolution from joint research conducted at the laboratories of photogrammetry and geodetic engineering of the Swiss Federal Institute of Technology of Lausanne .
Helimap System® is based on the combination of airborne Laser scanner and high resolution digital camera with direct georeferencing technology (GPS-INS). Helimap System® integrates 4 high tech sensors into a single original handheld unit. The technical specifications are the following:
    Riegl Laser scanners permiting the measurements until 150'000 point/sec with a field of view (FOV) of 60°
    Hasselblad digital camera with 22 or 50Mpix with FOV of 57°
    Inertial measurement unit (IMU) iMAR
    Dual frequency GNSS receiver (GPS-GLONASS)

The combination of Laser and imagery brings several advantages on classical airborne technique:

    The multiple echoes permit to measure points trough vegetation
    Automated DSM/DTM measurement
    High density point clouds
    Imagery completes the information for orthoimages and interpretations
The manual operation of the system provides fundamental advantages on conventional airborne systems:
    Easy and affordable deployment, anywhere on the planet
    Independance from the helicopter type (usable with SA318, AS350, AS365, EC155, EC135, A109, MI-8)
    No calibration required
    Oblique or vertical mapping within the same flight, ensuring a constant accuracy whatever the slope
    Short setup time (30min) between the time the helicopter arrives and we take off


                  Vertical configuration                     Oblique configuration

Performance

The performance of the system can be described in terms of mapping accuracy (at the ground level) and the image sharpness. The following figures depict the accuracy for usual flying height of Helimap System® (300m above ground, 1:9'000 scale)

    Mapping accuracy

    The mapping accuracy is given by comparing the measurements with ground control points (GCP). Photogrammetric mapping accuracy refers to residuals to check points on ground illustrated in the chart 1, for the different Aerial-triangulation technique (AT: classic, AT-GPS: GPS aided AT, GPS-INS: direct georeferencing). Laser point cloud accuracy is divided into a relative and absolute component. The relative precision refers to the inner noise between crossing strips for example, while absolute refers to GCP's comparison. For each component, a precision value can be estimated depending on the ground surface. This is illustrated in the chart 2.

          
             Chart 1: Photogrammetric accuracy                       Chart 2: Lidar accuracy


    Image quality

    The image quality can be estimated with 2 components: the sharpness and the noise. The sharpness can be expressed by the number of pixels required to depict a brutal transition of radiometry (e.g. black-white). The smaller the number of transition pixels there is, the sharper the image. The noise characterizes the local radiometric variability on a color supposed uniform. It is now a known fact that the digital cameras are sharper and less noisy than the former analogue film cameras. The following graphics illustrates the differences between a Hasselblad H1D and an analogue handheld photogrammetric camera.

      Camera Digital H1, scale 1:9'000 Linhof + Film 200iso , scale 1:4'500
      Aspect
      Noise
      [gray scale value (gsv)]
      1.5 gsv
      6 gsv
      Sharpness
      [transition pixels]
      ½ pixel
      3-4 pixels

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