Transcript
Challenges to capturing data: Field crews are faced with many challenges and difficulties when it comes to GIS data collection. The use of GPS in mapping is a powerful tool, but there are times when it has its limitations. Often the GPS satellite signal is blocked by obstructions such as trees, steep terrain or high-rise buildings. Additionally, a GPS receiver is inherently designed to compute the locations of its antenna. This means that in order to capture the location of a feature, you need to occupy that location. This is not always safe or practical when positioning features such as a gauging station in the middle of a stream or a manhole in the middle of the street. Benefits of Offsets in GPS Data Collection
• Makes data collection easier in
hostile environments. • Decreases safety liabilities in dangerous situations. • Reduces travel time to sites and objects. • Allows you to record offsets and attributes of hundreds of features from one location. • Eliminates extra manpower needed to collect data. • Saves time, money and resources.
Offsets: Making the job easier and safer The ability to apply offsets to features by recording both a GPS position and an associated distance and direction to the object of interest is very useful in challenging situations. For example, suppose you wish to record the attributes of a tower that is on the other side of a steep, narrow ravine. Rather than risk injury climbing across the ravine, you can use the offset capability to stand and record the position at one side of the ravine then simply record the offset to the tower on the other side. The entry of offset information can be estimated without measurement tools or obtained more accurately from a laser positioning system. By integrating a laser rangefinder and an electronic compass (providing distance, inclination and azimuth) with your GPS, you can significantly reduce travel time associated with field data collection by eliminating the need to physically occupy every point. The offset function allows you to stay at one location and record the offsets and attributes of hundreds of features before moving to the next location to do the same. Whether you are in need of 2D or 3D measurement, it is important that the laser rangefinder has the ability to measure a vertical angle and output horizontal distance. This will provide the most accurate positioning for 2D data and would also allow the you to gather 3D data if needed. Examples of Laser Offset Applications
• Mapping location of objects in steep terrain. • Safe recording of data near busy highways. • Mapping of gauging stations in middle
of streams. • Mapping of manholes and other features located in the middle of the street. • Positioning features where the GPS signal is blocked by buildings or trees. • Mining applications such as stockpile volume, general mapping & face profiling. • Mapping features which are on private property.
MapStar Angle Encoder
MapStar Compass Module II
The MSAE calculates a turned, horizontal angle between some reference point and the object being targeted. It will always require a second, known point to be available to sight as a reference. This directional information is then coupled with range and tilt from the Impulse to provide all the data necessary to derive X, Y, Z coordinates for the target. Combine this laser system with GPS to obtain +/- 0.1° offset position accuracy. A key feature of the MSAE is that it's not affected by local magnetic interference.
The MSCM II calculates azimuth readings referenced to magnetic North, True North or user-defined coordinates. This azimuth information is then coupled with range and tilt from the Impulse to provide all the data necessary to derive X, Y, Z coordinates for the target. Combine this laser system with GPS to obtain +/- 0.3° offset position accuracy. This new generation electronic compass requires field calibration in order to adapt to local magnetic interference, but it only takes about 60 seconds to perform.
TM
TM
How Much Error Can You Afford? Even 1.5° of error in a compass can result in over 13 feet of horizontal error when shooting to an object/feature 500 feet away! Additional errors may also become a factor if there is improper calibration or if the compass becomes out of level. LTI's modular design allows you to pivot the laser rangefinder 90° up or down while maintaining the compass sensor level. LTI's system is engineered with an emphasis on accuracy to limit further degradation of sub-meter GPS data. Laser Offsets at 500 Feet Away:
Laser Offsets at 100 Feet Away: Equipment
Accuracy
LTI's AE LTI's CM II Competitor A Competitor B Competitor C
0.1° 0.3° 0.5° 1° 1.5°
Error Equation SIN SIN SIN SIN SIN
(0.1) (0.3) (0.5) (1.0) (1.5)
X X X X X
100 100 100 100 100
ft. ft. ft. ft. ft.
Hz Error = = = = =
+/+/+/+/+/-
0.17 0.52 0.87 1.75 2.62
Key Advantages to Laser Technology's Positioning Systems • Both systems are quick and easy to use. • Offer industry leading accuracy, reliability and support. • Integrate seamlessly with every major GPS on the market and most popular software. • Modular design allows full tilt range of our rangefinder while maintaining azimuth/angular accuracy. ©2004 Laser Technology, Inc. All rights reserved.
ft. ft. ft. ft. ft.
Equipment
Accuracy
LTI AE LTI CM II Competitor A Competitor B Competitor C
0.1° 0.3° 0.5° 1° 1.5°
?
Error Equation SIN SIN SIN SIN SIN
(0.1) (0.3) (0.5) (1.0) (1.5)
X X X X X
500 500 500 500 500
ft. ft. ft. ft. ft.
Hz Error = = = = =
+/+/+/+/+/-
0.87 ft. 2.62 ft. 4.36 ft. 8.73 ft. 13.09 ft.
Did you know that LTI's Impulse laser has a built-in offset function? For example, you can account for the separation between the laser and GPS antenna when you are using a backpack.The offset function can also be used when you are only able to shoot to the outside of a feature but want the measurement to the center, such as a large diameter tree or telephone pole.
GPS Laser Positioning Systems
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