Orbitas Field allows you to collect an offset location using several supported methods.
The first and more accurate method is utilizing an external laser range finder.
The second is to utilize the camera on the iOS device.
While the second method is not at as accurate as the first , it is a convenient and fast way to collect an offset location. Read below for further details.
Start by opening a job and collecting a LOCATION like normal.
You can use Tap to Place, Integrated Services, or a connected Asteri GNSS.
However, please note, the calculated position will be affected by the accuracy of the starting point for offset.
See the section further down on “Understanding the math behind an offset”
Before Clicking Save… Select the OFFSET ICON shown below:
Shoot your target with your laser range finder.
Type in the offset values from your rangefinder in the appropriate fields.
Click SAVE to commit changes in Laser Offset Form
Click SAVE on the Location Form just as you would for any other Location.
In the example below we utilized the a TruePulse LTI 360. The more accurate the offset device, the better the results.
Please keep in mind: You need to supply a “True North” offset with valid compass calibration (see manufacturer instructions). Also, a projected XYZ must be used for accurate triangulation. In order to do this in Orbitas , you need a good internet connection.
Offset is displayed at the corner of the building we were shooting to, this is a successful offset.
*Note on Bearing:
Each laser manufacturer is different, so you must consult your manufacturer about the “type” of bearing being sent. We expect True North as mentioned above. The LTI 360 has the ability to enter in the “Declination” for your region. We have found this site to be great for finding values for your work area:
https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml
Begin by collecting your Location as before, and then selecting the offset tool as in the first example.
Select the “*” Icon to the right of the BEARING field.
The target is now displayed in a camera form. There is a small “ BOX ” we will call the “TARGET” in the center of the form. It is critical that the bottom of the target you are shooting at, is at the same “LEVEL” as the height the antenna collecting the position is placed. (with a 2meter antenna height on the rover, shoot a target 2meters up on structure.)
Next, ensure that the HEIGHT on the slider bar is the exact height as the camera lens on the iOS device. We recommend physically mounting the iOS device to a range pole or tripod on a pivoting mount. *In this example, the device was handheld, and you will see minor triangulation issues due to this.
Click SAVE after placing the target on the structure.
Target Box: Ensure to place the target but at the Antenna height, not ground level.
Camera Lens Height: Use this slider to adjust your camera height.
Save Icon: Click the save icon after setting target and adjusting the camera height.
Offset form is automatically filled out. However, notice the inclination. We had to “tilt” the iPad to get the camera focal length on the structure, so the iPad thought it was a +1 Degree tilt, we know from our laser offset, that this was downhill at 5 Degrees. This would create around a 10 foot error in distance for a 100 foot offset. So the key to using the iPad, is to do as close to level offsets as possible and then simply “zero” the Inclination!
Bearing is fairly close (remember 289 is the actual, but 285 is not bad for a short offset, but just like with inclination, 5 Degrees of error is about 10 foot of error XY at a 100 foot offset, so again use caution.
Distance is additionally erroneous because of the “Camera Height” shown on the previous slide. In this example we intentionally entered 5’ 6”, knowing the camera height was only 4’11”. Errors in Camera height = Errors in Distance calculated.
Click SAVE as before to save your offset and return to the map screen.
The resulting offset, while reasonable for some applications is about 10 feet from our desired target due to the errors listed above.
The math in the below screen shot confirms our offset just performed. It assumes an inclination of 0 Degrees (or level ground). Actual offsets are slightly more complex, because we must consider the Z value as well. That is why the antenna position and target (antenna height) are so critical, especially as offset distance increases.
To prove how accurate the offset function can be at longer offset distances, we show an example below… You can perform your own tests like this as well, using nothing but the Tap to Place feature within Orbitas and the Google Earth program.
Inside Google Earth , measure two visible items (not on structures that may have vertical distortion. I chose a Parking space and the BASE of a light pole. Google automatically gives us a “True North” bearing and “Map Length”. Map length incidentally is the 2D length, removing the Z factor mentioned before.
Within Orbitas use Tap to Place on the start point and collect a point. Tap to place a second point in the same location and enter in the Map Length, Heading and 0 Inclination into the offset form.
The results of a 350 Foot offset are below.
