Reflectorless total station (RLTS) has made it possible for only one person to carry out field measurements and inaccessible points can be measured with relative ease. There is no sufficient information about the accuracy of these instruments for the long range measurements. This paper attempts to evaluate the accuracy of reflectorless distance measurements ranging up to 1000 m and to determine the surface area needed for such measurements at different incidence angles. An experiment was carried out to examine what effect surface material, target size and incidence angle had on distance measurement. In this experiment 10 different distances were measured using targets of 6 different materials and 4 different sizes at 5 different incidence angles. To properly evaluate the results, a special supporting base was designed and manufactured for holding the reflecting targets to ensure accuracy in the evaluation. Based on the accuracy analysis of a lot of testing results, the conclusions that were drawn indicated that the target size had a great effect on the accuracy if the incidence angle was between 15 ° and 30 °.
Total station is widely used to survey topography and monitor land form, land use, geomorphic change detection of rivers, streams, beaches and mass wasting of hill slopes [
This paper studies the effect of target material, target size and incidence angle of laser beam on the accuracy of reflectorless measurements for distances up to 1000 m. A series of experimental measurements for 10 different distances were carried out using targets of 6 different materials and 4 different sizes at 5 different incidence angles. The distances obtained by reflectorless surveys were compared to the distances obtained by prism surveys. As the result of these comparisons, accuracy analyses were performed to draw conclusions about the influence of the mentioned parameters on the accuracy of reflectorless measuring.
The total station used in this research was TOPCON GPT-7501 (7W2024). Its specifications [
A special supporting base was essential so that the targets could be properly and accurately placed. A simple base of (U) shape cross section was designed. It is 2 cm wide, 3 cm depth and 20 cm long with a screw on the rear plane so that the fastening materials to it are facilitated. It is made by stainless steel and manufactured to secure that the internal surface of the front plane must be on the center of the screw on its bottom. A horizontal circle was added to facilitate rotating the target to the needed incidence angle of the laser beam on the target surface as shown in
The procedure that was applied is the following:
1) A line of 1000 m length is marked with nails every 100 m on a street near King Abduaziz University as shown in
2) The instrument is set up on the first point and its setting is modified to measure distance in fine mode and repeats the measurements 10 times.
3) The prism is centered on the next point, 100 m away. The distance between the instrument and the prism is measured after setting the instrument in prism mode.
4) The prism is removed from the tribrach and the special base is installed on it. The instrument’s telescope is
not moved during these changes. All 24 targets used in the experiment are in turn―according to the target size―installed on the base and the distance to each one measured after setting the instrument in reflectorless mode. The reflectorless distance measurements were carried out at 5 different incidence angles of the laser beam on the surface, 0˚ (normal), 15˚, 30˚, 45˚ and 60˚.
5) Steps 3 and 4 are repeated for the next 9 points, i.e. distances 200 m to 1000 m.
The difference between the measured distance on the prism (DP) and the reflectorless measured distance on each material (DNP) was calculated using Equation (1)
The acceptable value of ΔD is given by the Equation (2) [
where:
The acceptable values of the difference ΔD for confidence levels of 95%, for instrument used are:
Normal mode: ± 5.39 x95% = ± 10.5 mm
Long mode (up to 1000 m): ± (10.2 to 20.1) x95% = ± (19.89 to 39.2) mm
The differences ΔD in mm for the measured distances are summarized in Tables 1-10. The symbol (------) means that the instrument did not measure the distance to the target. The values of the differences ΔD, which are unacceptable for confidence level 95%, appear in bold. The tables show that in general, the reflectorless distances are shorter than distances measured on prism except for distances measured to targets of size 30 cm ´ 30 cm at incidence angles 30˚, 45˚ and 60˚. This may be because of the divergence of the laser beam over the target
Target size 5 ´ 5 | Target size 10 ´ 10 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | −4 | −1 | −2 | −4 | −4 | −5 | 0 | 1 | −1 | −1 | −3 | −3 | |
200 | −7 | −7 | −5 | −10 | −2 | −10 | −5 | −5 | −9 | −6 | −9 | −8 | |
300 | −8 | −5 | −15 | −11 | −15 | −12 | −5 | −4 | −15 | −5 | −8 | −4 | |
400 | −13 | −12 | −6 | −14 | −8 | −8 | −8 | −4 | −12 | −11 | −9 | −7 | |
500 | −4 | −9 | −8 | −8 | −8 | −3 | −11 | −12 | −9 | −10 | −13 | −17 | |
600 | −26 | −22 | −17 | −6 | −14 | −27 | −12 | −14 | −15 | −21 | 1 | −15 | |
700 | −25 | −14 | −24 | −12 | −18 | −16 | −16 | −20 | −21 | −17 | −9 | −2 | |
800 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
900 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
1000 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ |
Target size 20 ´ 20 | Target size 30 ´ 30 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | −1 | −1 | −5 | −4 | −2 | −5 | −2 | −7 | −5 | −3 | −9 | −4 | |
200 | −8 | −4 | −3 | −6 | −8 | −8 | −3 | −2 | −5 | −3 | −13 | −10 | |
300 | −3 | −4 | −5 | −6 | −11 | −7 | −3 | −1 | −6 | 0 | −15 | −10 | |
400 | −11 | −10 | −9 | −6 | −17 | −6 | −6 | −4 | −1 | −5 | −10 | −7 | |
500 | −11 | −9 | −12 | −7 | −16 | −16 | −14 | −10 | −13 | −9 | −12 | −18 | |
600 | −14 | −17 | −29 | −22 | −16 | −26 | −12 | −14 | −17 | −13 | −22 | −22 | |
700 | −7 | −14 | −14 | −11 | −5 | −17 | −5 | −4 | −16 | −8 | −10 | −13 | |
800 | −11 | −15 | ---- | −13 | ---- | −20 | 0 | −1 | −12 | −5 | ---- | 7 | |
900 | −22 | −16 | ---- | −2 | −17 | −15 | −20 | −22 | −15 | −2 | −9 | −14 | |
1000 | −41 | −17 | ---- | −22 | −18 | −12 | −22 | −8 | −9 | −7 | −17 | −30 |
Target size 5 ´ 5 | Target size 10 ´ 10 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | −1 | 2 | −2 | 0 | −4 | −4 | 2 | 3 | −1 | −1 | −3 | −4 | |
200 | −11 | −7 | −10 | −5 | −2 | −2 | 0 | −1 | −1 | −3 | −8 | −2 | |
300 | −9 | −11 | −4 | −15 | −16 | −23 | −5 | 2 | −7 | −3 | −20 | −2 | |
400 | −12 | −16 | −15 | −4 | −26 | −12 | −3 | −9 | −23 | −9 | −11 | −11 | |
500 | −7 | −10 | 2 | −8 | −25 | −3 | −18 | −17 | −20 | −12 | −20 | −25 | |
600 | −23 | −24 | ------ | −9 | ------ | −30 | −9 | −12 | −16 | −17 | −29 | −21 | |
700 | ------ | ------ | ------ | ------ | ------ | ------ | −19 | −16 | ------ | −11 | ------ | ------ | |
800 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
900 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
1000 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ |
Target size 20 ´ 20 | Target size 30 ´ 30 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | 0 | −2 | −3 | −2 | 1 | −4 | 1 | −6 | −4 | −1 | −8 | −6 | |
200 | −4 | −3 | 0 | −2 | −5 | −3 | −2 | −1 | −1 | −2 | −8 | −4 | |
300 | 8 | 1 | −4 | −2 | −4 | −16 | 6 | 4 | −2 | 2 | 1 | −9 | |
400 | −12 | 0 | −7 | −7 | −32 | −5 | 5 | 3 | −17 | 0 | −5 | −14 | |
500 | −1 | 0 | −3 | −6 | −4 | −14 | −4 | −4 | 3 | −3 | −10 | −17 | |
600 | −1 | −10 | −9 | −8 | −8 | 14 | 0 | −11 | −1 | −13 | −14 | −11 | |
700 | −7 | −17 | −10 | −2 | ------ | ------ | −14 | 0 | −10 | −12 | ------ | ------ | |
800 | ------ | −14 | ------ | -13 | ------ | ------ | 4 | 3 | −3 | −2 | ------ | ------ | |
900 | -23 | −15 | ------ | -26 | ------ | ------ | −12 | -7 | ------ | −4 | ------ | ------ | |
1000 | ------ | −8 | ------ | -17 | ------ | ------ | −12 | 2 | ------ | −13 | ------ | ------ |
Target size 5 ´ 5 | Target size 10 ´ 10 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | 3 | 1 | 1 | −1 | −10 | −9 | 4 | 4 | 1 | 1 | −2 | −13 | |
200 | −5 | −11 | −10 | −3 | −20 | −25 | −2 | 1 | −1 | 0 | −6 | −8 | |
300 | −11 | −9 | −10 | −13 | −28 | −24 | −3 | −1 | −3 | −10 | −25 | −21 | |
400 | −20 | −13 | −27 | −14 | −18 | −30 | −5 | −6 | −14 | −15 | −10 | −19 | |
500 | −12 | −9 | −10 | −7 | −19 | −3 | −13 | −8 | −4 | −10 | −27 | ------ | |
600 | −33 | −23 | ------ | −20 | ------ | ------ | −20 | −5 | ------ | −15 | ------ | ------ | |
700 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | -2 | ------ | ------ | ------ | ------ | |
800 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
900 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
1000 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ |
Target size 20 ´ 20 | Target size 30 ´ 30 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | −1 | −1 | −1 | 2 | −1 | −15 | 4 | −3 | 1 | −1 | −7 | −61 | |
200 | 2 | 1 | 5 | 1 | −2 | −29 | 5 | 5 | 1 | 4 | −4 | −33 | |
300 | 4 | 6 | 4 | 1 | ------ | 3985 | 4 | 14 | 5 | 7 | ------ | 3820 | |
400 | −11 | −1 | −2 | −7 | ------ | ------ | 14 | 1 | 7 | 5 | ------ | ------ | |
500 | 11 | 9 | 6 | 4 | 3 | −20 | 9 | 10 | 7 | 7 | ------ | ------ | |
600 | 4 | 11 | −6 | −2 | ------ | ------ | 1 | 18 | 4 | 0 | ------ | ------ | |
700 | −8 | −10 | ------ | −14 | ------ | ------ | 9 | 7 | −3 | 4 | ------ | ------ | |
800 | ------ | ------ | ------ | −11 | ------ | ------ | −3 | 9 | −16 | −7 | ------ | ------ | |
900 | ------ | −15 | ------ | ------ | ------ | ------ | 5 | 9 | ------ | −1 | ------ | ------ | |
1000 | ------ | −16 | ------ | −15 | ------ | ------ | −14 | 4 | ------ | −9 | ------ | ------ |
Target size 5 ´ 5 | Target size 10 ´ 10 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | 1 | 3 | 3 | −2 | −21 | −24 | 5 | 5 | 2 | 3 | −6 | −141 | |
200 | −9 | −13 | −13 | −5 | −25 | −10 | −1 | 4 | −3 | −3 | −24 | −53 | |
300 | −18 | −9 | −19 | −15 | −9 | −31 | −6 | −1 | −17 | −19 | −31 | −6 | |
400 | −13 | −19 | −20 | −21 | −28 | 0 | −24 | −12 | −17 | −17 | −25 | −20 | |
500 | −11 | −5 | −5 | −12 | −7 | −17 | −16 | −13 | −14 | −13 | −24 | ------ | |
600 | ------ | ------ | ------ | ------ | ------ | ------ | −13 | 0 | ------ | −9 | ------ | ------ | |
700 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
800 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
900 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
1000 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ |
Target size 20 ´ 20 | Target size 30 ´ 30 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | −1 | −1 | 2 | 4 | −4 | 3639 | 6 | −2 | 3 | 5 | −13 | 3583 | |
200 | 10 | 12 | 12 | 7 | −2 | 3576 | 14 | 13 | 6 | 14 | −10 | 3549 | |
300 | 6 | 0 | 3 | 0 | ------ | ------ | 6 | 14 | 2 | 16 | ------ | 3797 | |
400 | −8 | −3 | −10 | 3 | ------ | ------ | 23 | 0 | 4 | 11 | ------ | ------ | |
500 | 10 | 13 | 17 | −5 | −14 | ------ | 7 | 11 | 21 | 17 | ------ | ------ | |
600 | −1 | 3 | −9 | −8 | ------ | ------ | 2 | 18 | 14 | 9 | ------ | ------ | |
700 | −19 | −16 | ------ | −18 | ------ | ------ | 1 | 5 | −16 | 6 | ------ | ------ | |
800 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | 3 | ------ | −14 | ------ | ------ | |
900 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | 14 | ------ | 5 | ------ | ------ | |
1000 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | 8 | ------ | −25 | ------ | ------ |
Target size 5 ´ 5 | Target size 10 ´ 10 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | −8 | 1 | 0 | −8 | −22 | −22 | 6 | 6 | 3 | 2 | −5 | 4283 | |
200 | −16 | −6 | −14 | −10 | −13 | −15 | −4 | −1 | −11 | −5 | −16 | −53 | |
300 | −12 | −10 | −16 | −24 | −32 | −15 | −18 | −8 | −16 | −18 | −34 | −16 | |
400 | −18 | −15 | −21 | −9 | −14 | −24 | −35 | −11 | −20 | −8 | −26 | −45 | |
500 | −9 | −13 | ------ | −2 | ------ | −13 | −22 | −21 | −12 | −11 | −24 | ------ | |
600 | ------ | ------ | ------ | ------ | ------ | ------ | −5 | −18 | ------ | ------ | ------ | ------ | |
700 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
800 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
900 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
1000 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ |
Target size 20 ´ 20 | Target size 30 ´ 30 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dmm | Dmm | ||||||||||||
Dist | Concrete | Rock | Brick | Wood | Steel | Aluminum | Concrete | Rock | Brick | Wood | Steel | Aluminum | |
100 | −1 | 8 | 8 | 9 | −2 | 4096 | 9 | −1 | 9 | 8 | −13 | 3985 | |
200 | 22 | 13 | 22 | 15 | 3 | 4063 | 27 | 30 | 17 | 13 | ------ | 3903 | |
300 | −7 | −10 | −5 | −13 | ------ | ------ | −14 | 13 | 10 | 6 | ------ | 4368 | |
400 | −4 | −13 | −22 | −19 | ------ | −104 | 19 | −99 | 5 | 8 | ------ | ------ | |
500 | 12 | 12 | −9 | −13 | −13 | ------ | −5 | 12 | 35 | 18 | ------ | ------ | |
600 | 9 | −8 | −3 | 0 | ------ | ------ | 10 | 15 | 13 | 7 | ------ | ------ | |
700 | ------ | −22 | ------ | −32 | ------ | ------ | 0 | −1 | 13 | 19 | ------ | ------ | |
800 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
900 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | |
1000 | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ | ------ |
that make the instrument measures distances longer than that measured on the prism. Tables 1-10 show also that a target of size 5 ´ 5 cm and 10 ´ 10 cm can be used to measure distances up to 700 m at incidence angle = 0˚ and up to 500 m at incidence angles up to 60˚.
A target of size 20 ´ 20 cm can be used to measure distances up to 1000 m at incidence angle = 0˚ and up to 700 m at incidence angles greater than 30˚. The light color targets of size 20 ´ 20 cm can be used to measure distances up to 1000 m at incidence angles up to 30˚.
A target of size 30 ´ 30 cm can be used to measure distances up to 1000 m at incidence angle = 0˚ and up to 700 m at incidence angles greater than 45˚. The light color targets of size 30 ´ 30 cm can be used to measure distances up to 1000 m at incidence angles up to 45˚.
Steel target has an opposed behavior to the light color targets, as noticed from Tables 1-10. As the steel target size increases its ability to reflect the laser beam to the instrument decreases especially for incidence angles greater than 15˚. While steel target of size 5 ´ 5 cm and 10 ´ 10 cm can be used to measure distances up to 500 m, target of size 20 ´ 20 cm and 30 ´ 30 cm could not be used to measure distances greater than 200 m. This may be because of the darkness of this material.
Aluminum target has a unique behavior, as it act as a mirror with target size 20 ´ 20 cm and 30 ´ 30 cm when the incidence angle increases 15˚ as shown in
To show the effect of the incidence angle on the accuracy of the measured distance, the average of the absolute deviations for all materials was calculated after eliminated the odd values and presented graphically in
This research was performed to evaluate the accuracy of long range reflectorless total station used in urban areas where the targets were made of different materials and the site conditions forced the observation angle to be not perpendicular to the targets From the results gotten from the experimental work of this research, the followings can be concluded:
1) The keystone of the experiment is the supporting base, which is designed and manufactured to assure the correct placement of all targets and the possibility to compare the measured distances to the true values.
2) The majority of the reflectorless measurements are shorter than the true distances.
3) A target size of 5 ´ 5 cm could be used to measure distances up to 700 m at incidence angle = 0˚ and distances up to 500 m at incidence angles up to 60˚.
4) A target size of 20 ´ 20 cm could be used to measure distances up to 1000 m at incidence angle up to 30˚ and distances up to 700 m at incidence angles up to 60˚.
5) Target size has no effect on the accuracy of the measured distance at incidence angle = 0˚
6) Target size is in direct proportion to the measuring accuracy at incidence angles 15˚ and 30˚ and has a slight positive influence on the accuracy at incidence angles greater than 30˚.
7) The incidence angle up to 30˚ has approximately no influence on the accuracy of the measured distances or the measuring range.
8) The incidence angle greater than 30˚ decreases the accuracy of the measured distances and reduces the measuring range.
9) The measuring range is reduced dramatically with enlargement of the target size of steel and aluminum at incidence angles greater than 15˚.
10) Aluminum targets may act as mirrors at incidence angles greater than 30˚.
Thanks are due to Mr. Talal Al-Thebety and Mr. Said Hesiki for assistance in performing the field measurements.
RagabKhalil,11, (2015) Accuracy Evaluation of Long-Range Reflectorless Distance Measurement. Positioning,06,61-70. doi: 10.4236/pos.2015.63007