Trimble V10 Tech Tips part 2/2

Trimble V10 Tech Tips part 2/2

Trimble V10 Imaging Rover: Optimum Angle Intersection Areas

Products

  • Trimble® V10 Imaging Rover

Question

How should I configure my Photo Stations with the Trimble V10 Imaging Rover to obtain optimum intersection areas?

Answer

Within the green area, you can achieve suitable intersection angles for two photo stations. Outside this area the angles are too small and in the area between the stations the angles are too large (unless the object is vertically away from the baseline):

The V10 Imaging Rover works with 12 cameras in a panorama composition; output is one panorama for each station and the same intersection conditions are applied on the other side of the baseline:

You can enlarge the covered area by collecting additional photo stations. Some more simple examples are shown in the images below.

This is a possible V10 configuration to survey the façade of a building. Consider that the normal equations of the bundle adjustment will be singular if all control points (for example, station points measured with GNSS) are located on a spatial straight line. You can avoid numerical problems by adding some control points at or around the object.

There is another recommended way to get around those issues – clearly displace every second station from the straight line. Without any additional work you will have the shown configuration if you need to measure objects on both sides of the baseline.

If you spread out the stations in two directions, you will get a stable configuration.

Use this configuration if there are buildings around and some topographic features in the courts need to be measured. Another application could be measuring the features of a road junction.

Longer baseline lengths are obtained by having the diagonally located panoramas. Longer distances are then possible without worsening the intersection conditions. A limitation in distance is only given by the required accuracy at the object.

Additional photo stations in the center of the area, as shown schematically below, will give more flexibility in redundant intersections.

Trimble V10 Imaging Rover: System Goals

Products

  • Trimble® V10 Imaging Rover
  • Trimble VX™ Spatial Station
  • Trimble R10 GNSS receiver
  • Trimble Access™ software
  • Trimble Business Center software
  • Trimble VISION™ technology

Question

What are the goals for the Trimble V10 Imaging Rover system?

Answer

On the Trimble VX Spatial Station, VISION technology was located on the total station. Images could be used for visualization, documentation, and photogrammetric purposes.

However, a total station is not always set on the best place to image objects. Without resetting the instrument, there are often hidden areas that are not shown in the VX panoramas. Taking panoramas with a total station also takes time.

On the Trimble V10 Imaging Rover, the VISION technology was relocated to the rover, which means that the technology can now be used in a more flexible way. It is not just a camera on a pole – multiple sensors work collectively to produce a coordinated end result. In effect, twelve cameras generate a panorama with a simple click.

The Imaging Rover can be integrated seamlessly in a project with a Trimble R10 GNSS receiver or a total station, controlled in the field with the Trimble Access field software, and processed in the office with Trimble Business center software. In this way, field and office software take the complexity of photogrammetry and make it a practical tool for everyday survey practices.

Even measurements using a GNSS receiver will get a specific appreciation in value. With a GNSS receiver you can normally measure only those ground points on which the GNSS rod can be placed. Indirect or eccentric measurements are always difficult and time consuming to obtain in the field. However, vertical objects can easily be captured with the V10 Imaging Rover and both visualization and documentation by imaging are now possible in combination with GNSS measurements. Even objects in shadowed areas can be measured – this is valid for both GNSS and total stations.

Some benefits for a surveyor when using the Trimble V10 Imaging Rover in both field and office software are as follows:

  • Obtain more reliable data.
  • Capture more information with less effort.
  • Obtain more position data with less GNSS points.
  • Obtain remote position data.
  • Capture visual data.
  • Provide new deliverables to the customer.
  • Move survey tasks from field to office.
  • Enable office crew to visualize the work site and extract information.
  • Measure in areas of GNSS shadow.
  • Measure in areas outside the robotic total station’s viewing area.

Trimble V10 Imaging Rover: Object Conditions and Restrictions

Products

  • Trimble® V10 Imaging Rover

Question

Can you recommend photo station configurations in complex site conditions?

Answer

Objects to be measured are not always accessible without restrictions and not all parts of an object are visible with the same quality. That means that you will have to accept restrictions concerning the optimum location for the rod and the required intersection geometry. This can partly be balanced in the poor object areas by an increased number of panoramas.

Some simple examples are given here to help users positioning the V10 Imaging Rover in different scenarios.

Ensure that all structures in this corner can be measured with optimum intersection angles.

The distance between the houses may often be too small to have photo stations between them. The image shows a configuration for this scenario.

The base length on both sides of the houses must be adapted to the available space between them to ensure sightings along the houses.

It is easy to find a good configuration with simple examples, such as if you have only one façade. However, if the situation is more complex, for example, an ensemble of several buildings, it is more difficult. In those cases, concentrate on each building and find a separate configuration for each of them. This may result in a more photo stations than you would like to have, but you will possibly have good conditions for each of the objects inside the project.

Select for example 3 photo stations for each object like shown in the image.

Than focus onto the third building only with another set of 3 stations:

And then onto the next one:

Trimble V10 Imaging Rover: Process from Panorama Exposure to Storage

Products

  • Trimble® V10 Imaging Rover
  • Trimble Business Center software
  • Trimble Tablet
  • Trimble Access™ software

Questions

What is the size of the panorama taken with the Trimble V10 Imaging rover?

Are the exposure measurements of the rover’s images done separately or uniformly?

Are the images exposed simultaneously?

Where is the panorama stored, in the camera head or on the Tablet computer?

Answers

Twelve calibrated 5 MP cameras are included in two levels of the camera head:

The measurement of the exposure is done separately for each camera.

However, the exposure itself is done simultaneously for all cameras.

The cameras deliver a 60 MP 360° panorama where the size of a panorama is between 10 and 20 MB. It is stored temporarily in the camera memory, displaying as thumb-nails, and downloaded to the Trimble Tablet when completed.

Trimble V10 Imaging Rover: Workflow in the Field

Products

  • Trimble® V10 Imaging Rover
  • Trimble Access™ software
  • Trimble R10 receiver
  • Trimble Business Center software
  • Trimble Tablet
  • Autolock® technology
  • VRS Now™ service

Summary

This document describes the general workflow in a project when measuring with the Trimble V10 Imaging Rover and an R10 receiver or a total station.

Technique

General Trimble recommendations:

  • Plan the photo stations with respect to the object area that you need to cover.
  • Set up the stations in a zig-zag pattern to stabilize the station geometry.
  • Take care of distances and intersection angles.
  • If you want to do the measurements in Trimble Business Center software manually, the base lines between the stations can be larger with respect to geometry.
    If you want to do it automatically, the stations should have smaller base lines to facilitate the matching.
  • A Trimble V10 Imaging Rover with a position sensor is not as light as the normal rover with a prism only or with only the R10 receiver on top. It may therefore be to your advantage to use the V10 Imaging Rover to measure the photo stations only, and measure all the other topo points using the normal rods.

Using the V10 Imaging Rover and a total station

To make it as simple as possible, the workflow describes measuring in a local system.

  1. Select a suitable location for the total station so that you can observe all photo stations to be measured later.
  2. Install photogrammetric targets at the object or around the object area if you need additional control points and/or check points. You can also use significant structures that you can measure well with the total station and in the images.
  3. Set up the V10 Imaging Rover with the camera head, the R10 360° prism on top, and the Trimble Tablet.
  4. Use a USB cable to connect the camera head to the Trimble Tablet.
  5. Start the Trimble Access software on the Trimble Tablet.
  6. Start a new job and then select the Scale 1.0 coordinate system.
  7. Perform a simple station setup routine using local coordinates, set the azimuth to zero, and measure it in Angles only mode.
  8. Measure the control points and checkpoints in DR mode in 2 faces to eliminate any collimation error.
  9. Switch on the Autolock technology.
  10. Select the R10 360° prism on top of the V10 Imaging Rover as a target.
  11. Measure the photo stations and capture the panoramas.

Note: Local systems are normally not north orientated. To avoid the measured magnetic azimuths trying to rotate the local system, you should disable the raw orientations in the Trimble Business Center software prior to any adjustment.

Using the V10 Imaging Rover and the R10 GNSS receiver

  1. Set up the V10 Imaging Rover with the camera head, the R10 receiver on top, and the Trimble Tablet.
  2. Use a USB cable to connect the camera head to the Trimble Tablet.
  3. Start the Trimble Access software on the Trimble Tablet.
  4. Make sure that there is a connection with the base station or a service such as VRS Now.
  5. Select the correct user coordinate system and the Geoid model.
  6. If you need control points and/or check points in the object area, select suitable ground points and measure them with GNSS.
  7. If you assume that the ground points will not be directly measurable in the images, set up normal rods on these points with a photogrammetric target on top. Remember to measure the target heights of the control points.
  8. If possible, set up the photo stations where they are not influenced by multipath and/or shadowing.
  9. Use the R10 GNSS receiver to measure the photo stations and capture the panoramas. Ensure that you are measuring control points that should be more accurate as normal topo points. It is recommended that you select a longer measuring time.

Trimble V10 Imaging Rover: Baseline Length versus Object Distance

Products

  • Trimble® V10 Imaging Rover

Question

How can I estimate the maximum baseline length when measuring, for example, to a plane façade?

Answer

One of the standard rules in close-range photogrammetry is that the angle between the photogrammetric sighting and the object surface (angle of incidence) should not be less than 20° for distinctive object structures. Sufficient projection sizes and contrasts can then be achieved (Luhmann 2010).

Even with angles of incidence greater than 20°, objects can lose their unambiguity: A corner or an edge of a window or house can appear extremely different in images aiming under different azimuths. Different distances and illuminations complicate the measurement in both images so that you cannot achieve a similar accuracy on both images.

With that rule, the maximum base length between two V10 photo stations can be calculated if the distance d between the camera rod and the object is given. It is assumed that the object is, for example, a plane façade as shown below:

Camera 4 may sight orthogonal to the object, for example directed to point A. The angle of incidence is 90°. Then, a point C can be seen with camera 5 under an angle of incidence of 20°. If you select the next V10 position close to this point, the angle of incidence will again be 90°.

Between points A and C, angles of incidence from both stations are between 20° and 90°. The intersection angles between both photo stations are in the range 70° to 108°.

The maximum base b between both stations can be calculated as follows:

A general rule that you can use is that the baseline length should not exceed 2.5 times the object distance to ensure good angles of incidence larger than 20° and intersection angles around 90°.

For b = 2d the following values are valid:

d b Angles of incidence Intersection angles
10 m 20 27° – 90° 68° – 90°

Reference

Luhmann, Thomas: Nahbereichsphotogrammetrie. Grundlagen, Methoden und Anwendungen. 3. Auflage, Wichmann Verlag, 2010

Trimble V10 Imaging Rover: Declination Angle when Measuring Magnetic Azimuths

Products

  • Trimble® V10 Imaging Rover
  • Trimble Access™ software
  • Trimble Business Center software

Question

What does declination mean and how can I calculate it?

Answer

The declination angle is required to correct measured magnetic azimuths in the Trimble V10 Imaging rover.

Magnetic declination, sometimes called magnetic variation, is the angle between magnetic north and true north. Declination is considered positive east of true north and negative when west.

Declination is calculated using the current World Magnetic Model (WMM) or the International Geomagnetic Reference Field (IGRF) model. The firmware in the V10 Imaging Rover holds the earth magnetic field based on the Epoch 2010, valid for about 5 years:

http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml

The magnetic azimuth and the declination angle change over time. So far they depend on geographic position and time. To obtain the current value, you can use a service of the NOAA, the National Geophysical Data Center of the US, available athttp://www.ngdc.noaa.gov/geomag-web/

  1. In this web site, enter your geographical coordinates and the date. The coordinates must be separated by a space, in the format deg min sec, as shown below for Denver Colorado:

  2. Select the format for the result and then click Calculate.

    The declination angle appears as shown below:

  3. Enter the declination value into Trimble Business Center. Select Project Settings/Computations/Device Orientation:

    East values will get a positive sign, west values a negative one.

Declination results are typically accurate to 30 minutes of arc, but be aware that several environmental factors can cause disturbances in the magnetic field, for example:

  • Armored concrete structures like walls and bridges
  • Steel structures
  • Cars
  • Lamp masts

Lateral impacts will change the local horizontal magnetic field and therefore the azimuth. Influences for example from the bottom (man hole covers, and so on) will only influence the vertical component and not the horizontal ones and therefore not the azimuth.

Note: If you do not trust the environment you can disable the raw orientation parameters in Trimble Business Center to avoid a wrong approximate azimuth in the bundle adjustment.

Trimble V10 Imaging Rover:  Accuracy of Eccentricity of the Camera Head

Products

  • Trimble® V10 Imaging Rover
  • Trimble R10 GNSS receiver
  • Trimble Access™ software
  • Trimble Business Center software

Question

How accurate can the eccentricity of the camera head be measured when the rod is tilted?

Answer

The tilt is measured by the tilt sensors in 2 directions. The tilt accuracy of both components is specified in the datasheet with 0.03°. However, not only the tilt accuracy has to take into account. Compared to a total station where the tilts are measured in specific directions – parallel to line of sight and trunnion axis – the orientation of the tilt measurements must be measured separately. This is done by the magnetic compass. The accuracy of the magnetic azimuth is mostly the larger impact on the accuracy of the eccentricity to get. In an undisturbed environment the accuracy of the magnetic azimuth is specified with 1°.

 

So, the eccentricity is influenced by the tilt and the azimuth error components.

The error parts of both components are shown in the graph versus the azimuth error, which may increase in disturbed areas. A tilt of 40’ is assumed, which results in an eccentricity of 24 mm of the camera head related to the tip of the rover:

  • The influence of the tilt dependent component is constant. It is not influenced by the azimuth error.
  • In the normal magnetic field (azimuth error = 1°) the tilt related accuracy is dominant.
  • The red line indicates also that the eccentricity cannot be calculated better than 1.5 mm. This accuracy fits well to the measurement accuracy of GNSS or a total station measurement to a 360° prism.
  • In disturbed fields the decreasing azimuth accuracy will have a larger impact onto the eccentricity error.

The graph above was developed with a constant small tilt. As it is allowed to use the V10 Imaging Rover with larger tilts, two other graphs are shown below, the left one for different larger tilts up to the limit of 15° and the right one for smaller tilts. As above the error of eccentricities are shown versus the azimuth error between 1° and 10°.

 

Magnetic disturbances affect large eccentricity errors when the rover is tilted to the limits of 15° as can be seen in the left graph.

If magnetic disturbances are expected you should level better than 40’ to reduce the eccentricity error.

If you level for example better than 20’, the eccentricity error will be 2-3 mm in maximum (right graph).

However, you should have always in mind that these parameters are only approximated values for the bundle adjustment. So far the accuracy question is not as important as for the Trimble R10 GNSS receiver where the measured position is reduced to the rod tip using the measured tilts and azimuth.

Note:      In Trimble Business Center the rotational parameters – azimuth and tilts – can be deactivated when the user is sure that the rover was standing close to disturbing objects.

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