The
"native" colours for an HDS (High Definition Survey) point cloud are
based on the reflectivity of the surface the measurement is made to and
are determined by the intensity of the received reflected laser beam.
Whilst this information is useful in its own right it is often desirable
to have the points with their “natural” (RGB) colours.
A method for adding the “natural” (RGB)
colours to the point cloud is to use 360° panoramic images created with
an external camera, usually fitted with a fisheye lens. This
method is particularly useful where the HDS Scanner does not have a
coincident fitted camera system, but can be useful even if there is one,
such as with the
Leica ScanStation C10, as it gives much
greater control over the photography and its manipulation and the images
can be recorded at one location whilst the Scanner is deployed at
another saving time in the field.
It
is imperative that the panoramic images are recorded with the
Entrance Pupil (Nodal Point) of the
camera lens at exactly the same location as the scanning centre of the
HDS equipment, although it is irrelevant a to whether the images are
recorded before of after the scan. To achieve this, Nodal Ninja
provide adaptors to be used with the
Nodal Ninja 3 manufactured by Fanotec.
The use of a Nodal Ninja 3 and
appropriate adaptor ensures that the
camera is at the correct height, but it is important to ensure that the
vertical axis of rotation of the camera system is coincident with
Entrance Pupil and the correct positions on the upper and lower arms of
the panoramic head will depend on the camera and lens being used.
Some lenses have a single
Entrance Pupil, but that for a fisheye
lens slides along the principal ray depending on the angle of incidence
and the gold ring is often considered to be the best location for
aligning the camera and lens with the axis of rotation, although this is
not always true as with the Samyang 8mm lens shown in the photograph, so
it is important to establish the correct point for the lens being used.
The next item to consider is the number of
images required for the panorama.
The greater the overlap between the images,
the better the chance of the stitching software (e.g.
PTGui) being able
to create good Control Points, but too great an overlap can cause
problems, so a good rule of thumb is to aim for 40% to 50%. The
perceived wisdom and general advice is to use six images at 60°
intervals with a
Sigma or
Samyang 8mm lens fitted to a camera with an APS-C sensor, which usually works, but can cause problems with both the
image matching algorithms when creating the Control Points and Blending
the images when creating the Equirectangular image. With this set
up, 8 images at 45° intervals provides a greater overlap giving the
stitching software (e.g. PTGui) a better chance of producing good
Control Points without any user intervention.
The
choice of letting the camera select the exposure or to set the exposure
manually will depend on the site conditions. Letting the camera
select the shutter speed and aperture will often produce good results,
but it is important to consider the point at which the camera is
measuring the exposure from. In poor lighting conditions, such as
in a room, the camera will usually select a wide aperture minimising the
“depth of field”, but it is likely that there is a large range in the
distances of the subject from the camera so a greater “depth of field”
is preferred, in which case setting the exposure manually or using
aperture priority with an aperture of
f8 or
f5.6
will give the best results. The photograph to the left shows the
camera exposing for the street whilst the one to the right has the
correct exposure for the subject of interest.
The same applies to focus. Using
autofocus can result in focusing on the wrong subject so using manual
focus, if available, is recommended. In this example the focus
will be on detail much further away than the subject of interest.
Also, lack of detail at the point the lens is attempting to autofocus on
will cause the lens to “hunt”, which could result in a “soft” (out of
focus) image or no image being recorded.
Using an aperture of
f8 or
f5.6
can result in slow shutter speeds, especially in poorly lit rooms, but
as the camera is mounted on the same tripod as used for the HDS Scanner
it is rock steady so this is not a problem. However, it is
recommended to use a remote release to avoid any camera movement during
long exposures.
As mentioned, the use of an external camera
solution provides maximum control over the photography. This does
not only apply to exposure, focus and white balance, but allows for HDR
(High Dynamic Range) photography to be used, which is a technique worthy
of investigation. This involves recording a set of images with
different exposure values (e.g. 7 images at 1 stop intervals giving a
range of -3 to +3 stops). Even if HDR is not going to be used it
is worth "bracketing" to ensure correctly exposed images as once the
tripod is moved it is not possible to replace the camera with the
Entrance Pupil at the same position as the Scanner centre.
The video shows the use
of an external camera to colour the point cloud
measured with a Leica ScanStation. The HDS
Scanner is then taken out of the tribrach and
replaced with a camera on a Nodal Ninja panoramic
head and HDR images are recorded for processing as a
panorama in software such as PTGui to create the
Cube Images for import into the Leica Cyclone
software.
This video was created
by
Plowman Craven, one
of the world's leading and most innovative geomatics
companies and a world leader in HDS, to illustrate
data collection for use with BIM (Building
Information Modelling).
This presentation has been prepared for the capture of Spherical Panoramas
for use with data scanned with Leica Laser Scanners, but the information
is also useful to anyone wishing to create Spherical Panoramas in their
own right.
To view this
file you will require
Acrobat Reader. If
you do not already have a copy, visit the
Acrobat site to download
the version for your operating system.
A
site that is being developed to relate specifically to panoramic
photography to show the potential of this media and how it is
able to convey much more than words or single images.
If a picture is worth a thousand words then a panorama must be
worth ten thousand, especially a 360° (or spherical) panorama
where you can look all around and in any direction you wish to.
One of the world's leading and most
innovative geomatics companies and a world leader in HDS.
Plowman Craven is a trusted name
which offers a broad range of measurement services across
numerous and diverse markets. Operating worldwide, their
highly skilled and motivated team make a difference by providing
timely, collaborative and accurate solutions to meet their
Customers requirements.
HDS
(High Definition Surveying) is the combination of EDM (Electromagnetic
Distance Measurement) and electronic Angle measurement to rapidly
measure a very large number of 3D points to Surveying and Engineering
precision.
Leica Geosystems'
product family includes powerful and versatile time-of-flight ranging
systems such as the Leica ScanStation C10 and ultra-high-speed,
phased-based ranging systems, such as the new Leica HDS6100. Leica
Cyclone and Leica CloudWorx software provide a full set of Leica-quality
geo-referencing, surveying, and CAD integrated engineering tools for
creating accurate deliverables and managing large scan data sets with
unparalleled ease.
Manual
for External Camera Workflow
After scanning with HDS, a camera, fitted to a special bracket, replaces
the scanner. The bracket is placed on the same tribrach the scanner
used. A fish eye lens mounted on the camera is positioned on the bracket
so that the focal centre of the lens matches the optical centre of the
scanner.
Using Thermal Images to create a 360° (Interactive) Panorama for use
with HDS Point Clouds
A
report on an investigation into the possibility of using
images from a Thermal Imaging Camera to create a 360° (Interactive)
Panorama to generate the Cube Images to attach the colours from the
thermal images to an HDS
(High Definition Survey) Point Cloud.
Taking
Panoramas
If a picture is worth a thousand words
then a panorama must be worth ten thousand, especially a 360° panorama
where you can look all around, but how are they created?
Links
include PanoramaStudio, PTGui, Pano2VR, panoramic tripod head suppliers
and 360° panoramas.
Determining the
Nodal Point of a Lens
For a lens
to be used effectively for
Photographic Intersection the
location of the Front Nodal Point must be
accurately determined.
Making use of the
Nodal Point of a Lens
Comments
on making use of the knowledge of the behaviour and location
of the Nodal point of a lens for various Panorama and
Photographic Intersection applications.
The Nodal Point
The case for the Nodal Point and usage of the term..
Focus and Exposure
Comments on getting the correct Focus and Exposure for
making Panoramas.
Lens Angle of View
The Angle of View of
a lens, or what the lens "sees", is useful for calculating
the number of shots and their orientation for 360° panoramic
photography.
Spherical
Panoramas with a Normal Lens
Using a normal (rectilinear) lens for Spherical (360°) Panoramas.
The
"native" colours for an HDS (High Definition Survey) point cloud are
based on the reflectivity of the surface the measurement is made to and
are determined by the intensity of the received reflected laser beam.
Whilst this information is useful in its own right it is often desirable
to have the points with their “natural” (RGB) colours.
It
is imperative that the panoramic images are recorded with the
The
choice of letting the camera select the exposure or to set the exposure
manually will depend on the site conditions. Letting the camera
select the shutter speed and aperture will often produce good results,
but it is important to consider the point at which the camera is
measuring the exposure from. In poor lighting conditions, such as
in a room, the camera will usually select a wide aperture minimising the
“depth of field”, but it is likely that there is a large range in the
distances of the subject from the camera so a greater “depth of field”
is preferred, in which case setting the exposure manually or using
aperture priority with an aperture of
f8 or
f5.6
will give the best results. The photograph to the left shows the
camera exposing for the street whilst the one to the right has the
correct exposure for the subject of interest. 
