In
geo-referenced flights, the accuracy of measurements made on the 3D model by
DatuBIM depends on the following parameters:
- The camera resolution and the distance between the
camera and the measured object. The accuracy of measurements made by DatuBIM is
a factor of the camera’s resolution and the proximity to the measured object.
Typically, a 20-megapixel camera provides a 1 to 2-centimeter (3 to 6 hundredth
of a foot) measurement accuracy at a distance of about 50 meters (150 feet).
- The precision with which measurements in the survey
area are done. This refers to the coordinates of the reference control points.
These should be as exact as possible as they set an accuracy baseline for all
the measurement and drafting related to the images. When you measure ground
control points, make sure you have several of them on a surface showing a very
clear feature, such as marks on the ground or marks on walls. Better yet, the
surveyors can paint their own marks, such as a cross of 60cm by 60cm (2 feet by
2 feet). This will assure that a very precise measurement is taken. It is very
strongly recommended to make two sessions of measurement, and take the
average. If the difference of
measurements of a specific point is more that 2-3 cm, consider disposing the
point or retaking the measurement.
- The scattering of the control points and the accuracy
of digitizing them in the images. For best measurement accuracy, control points
for image geo-referencing should be chosen on the perimeter of the surveyed
area so that measurements made on the 3D model by DatuBIM are interpolated,
rather than extrapolated. Moreover, control points should be well distributed
in 3D space, i.e., relative to both depth and height, and digitized as
accurately as possible in the geo-referenced images. For more details on
measuring control points in the field.
Various
quality control measures in DatuBIM provide the user with detailed information
about the accuracy of measurements. Firstly, after the images have been
geo-referenced, DatuBIM verifies the accuracy of the image geo-referencing by
comparing the relative orientation of the control points to the relative
orientation of the images. The Geo-Referencing Quality Indicator gives
an indication of the accuracy of the referencing of the photogrammetric model.
Furthermore, after calculating the coordinates of the new points measured from
the images, DatuBIM provides the accuracy of each measurement, i.e., the
(x,y,h) residuals for every point.