Αξιολόγηση της μέτρησης του μήκους και του ποσοστού της επιστρεφόμενης ακτινοβολίας με reflectorless γεωδαιτικούς σταθμούς

Abstract

Αντικείμενο της εργασίας αυτής είναι η μέτρηση του ποσοστού της επιστρεφόμενης ακτινοβολίας και του μήκους σε διάφορα υλικά σε τέσσερις διαφορετικές γωνίες πρόσπτωσης, με πέντε διαφορετικούς ολοκληρωμένους γεωδαιτικούς σταθμούς και η αξιολόγηση της ορθότητας και της ακρίβειας των αποτελεσμάτων που προκύπτουν. Στο πρώτο κεφάλαιο παρουσιάζονται κάποια γενικά στοιχεία για την ανακλαστικότητα, τη λειτουργία των γεωδαιτικών οργάνων, την εξέλιξη των γεωδαιτικών σταθμών μέχρι τη σύγχρονη εποχή, τη γενική αρχή λειτουργίας αυτών καθώς και τα σφάλματα που οφείλονται σε διάφορους παράγοντες όπως η ατμόσφαιρα. Στο δεύτερο κεφάλαιο περιγράφονται οι συνθήκες διεξαγωγής των μετρήσεων, η μεθοδολογία που ακολουθήθηκε στον εσωτερικό και τον εξωτερικό χώρο, τα τεχνικά χαρακτηριστικά των ολοκληρωμένων γεωδαιτικών σταθμών και τα υλικά που χρησιμοποιήθηκαν. Στο τρίτο κεφάλαιο εμφανίζονται πίνακες και διαγράμματα που παρέχουν πληροφορία σχετικά με τη διαφορά της τιμής του μήκους που προκύπτει από τη μέτρηση του πάνω σε κάθε υλικό με τη reflectorless λειτουργία, σε σχέση με το μήκος που έχει προκύψει από τη μέτρηση με χρήση ανακλαστήρα. Ακολουθούν τα διαγράμματα του ποσοστού της επιστρεφόμενης ακτινοβολίας ανά υλικό και για τον εσωτερικό αλλά και για τον εξωτερικό χώρο και γίνεται μια σύγκριση των αποτελεσμάτων που προκύπτουν. Έπειτα παρατίθενται τα διαγράμματα των αποστάσεων ως αποτέλεσμα των μετρήσεων που έχουν πραγματοποιηθεί με τον ολοκληρωμένο εικονογεωδαιτικό σταθμό Topcon GPT 7003i για τη διερεύνηση της επαναληψιμότητας- διασποράς των μετρήσεων με αυτόν το σταθμό. Τέλος, αναφέρονται τα προβλήματα που ανέκυψαν κατά την εκτέλεση όλων αυτών των πειραματικών μετρήσεων. Στο τέταρτο κεφάλαιο παρουσιάζεται η σύγκριση των αποτελεσμάτων της μέτρησης του μήκους στα 50m στον εσωτερικό και τον εξωτερικό χώρο με όλους τους ολοκληρωμένους γεωδαιτικούς σταθμούς και η σύγκριση των αποτελεσμάτων της μέτρησης του μήκους με τον ολοκληρωμένο γεωδαιτικό σταθμό Leica TCRM 1201 στον εσωτερικό χώρο σε συνθήκες τεχνητού φωτισμού και χωρίς φωτισμό. Ακολουθεί η σύγκριση της επιστρεφόμενης ακτινοβολίας για την απόσταση των 50m στον εσωτερικό και στον εξωτερικό χώρο. Στη συνέχεια, γίνεται αξιολόγηση της ορθότητας της μέτρησης του μήκους με όλους τους ολοκληρωμένους γεωδαιτικούς σταθμούς. Τέλος, στο πέμπτο κεφάλαιο παρουσιάζονται τα συμπεράσματα που προέκυψαν, οι προτάσεις και το χρονοδιάγραμμα των εργασιών για την εκπόνηση αυτής της μελέτης.

A few decades ago, the process of angle and distance measurement was time-consuming and it required a big team of individuals (persons), strong efforts and the result was not the desirable. However, the rapid technology development in a lot of sectors and especially in the topography, where many problems of Rural and Surveying Engineer are solved with the new total stations regarding to the time and the precision. The reflectorless total station is one of these developments. This diploma thesis deals with the investigation and the evaluation of reliability of the results of the distance measurement and the percentage of the returned radiation by using the reflectorless operation of total stations, namely without using a reflector. For this aim, 5 total stations (Leica TCR 405, Leica TCRM 1201, Topcon GPT 3003LN, Topcon GPT 3105N, Topcon GPT 7003i) were used, measurements on 21 materials, in 4 different angles of incidence of the laser beam and in two different distances, indoors and outdoors respectively were carried out. The materials that have been used are: • Kodak White Card (90%) • Kodak Gray Card (18%) • Self-adhesive glossy target • White cement • Gray cement • Grey cardboard • Black cardboard • White plastic • Red plastic • Grey floor tile • Beige(flesh-coloured) floor tile • Brown foam • White foam • Marble • Wood • Particle board • Melamine • Roof tile • Asphalt • Rock • Glass These experiments took place, indoors, in a laboratory room at the School of Rural and Surveying Engineering, which is used for metrological processes. Indoors, the distances were about 50m and 15m. Outdoors, the distances were about 50m and 200m, close to each instrument’s range. During the experiments, each instrument measured every different material one time in four different angles of incidence of the laser beam, perpendicular to the sighting direction and at 30°, 45° and 60° angle in relation to the previous direction (figure 2.1). Also, the percentage of the reflected radiation was measured. This process followed for all the total stations, except the Topcon GPT 7003i, which measured on every different material five times in all different angles in order to estimate the precision of the measurements. The conclusions of these experiments are presented below. General conclusions • The distance measurements without a reflector are particularly precarious. They are influenced by various factors and only in certain cases and under certain circumstances the measurement agrees with the nominal accuracy and the nominal range of the instrument that is used. • The bigger the range of the instrument is than the length to be measured, the more accurate the measurement is. Usually the range required is over twice the distance that needs to be measured when the laser beam is perpendicular to the surface of the material. Bigger range is required when the laser beam deviates from the previous position, in order the result to be according to the nominal accuracy for the majority of the materials that the Surveying Engineer meets in his field work. • The angle of incidence of the laser beam is the most important parameter which influence the credibility of the reflectorless distance measurement. • The distance measurement is not always correct and consequently not acceptable according to the nominal accuracy of the instrument. Hence it is not reliable. Therefore, it is preferable for an instrument not to measure at all than to provide wrong measurements. • In small distances, such as 15m, the total stations measure correct and precise according to their nominal precision. • In bigger distances such as 50m, the angle of incidence of the laser beam is decisive. The bigger the angle is, the less reliable the measurements are. • At the distance of 50m, in the angle of incidence of the laser beam perpendicular to the sighting direction all the total stations provide reliable measurements for almost all the materials. • At the distance of 200m, when the angle of incidence deviates from the previous direction, the total stations do not measure to many materials and even for the materials that they provide measurements, they are usually wrong. • At the distance of 200m, which is close to the range of the total stations used, they did not measure reliably nor in the Kodak White Card. • The glass has an odd behaviour. Since it is transparent, the laser beam aims to the material which is behind the glass and the length measured is over-estimated. The effect of the percentage of the reflected radiation • The percentage of the returned radiation does not always ensure reliable measurement. If the percentage is high, then the distance measurement is carried out. At the perpendicular angle of incidence of the laser beam to the surface material, a high percentage of the returned radiation ensures reliable distance measurements. However, as the angle deviates from the previous direction, it is observed that even if the percentage of the returned radiation is high, the measurement may not be acceptable for confidence level 95%. When the percentage is low, the measurement usually cannot be carried out. • The bigger the angle of turn of the material is, the lower is the percentage of returned radiation. • In small distances the returned radiation is higher than in bigger distances. • In the tunnel, where the conditions of temperature, humidity, pressure and lighting are steady, the returned radiation is higher than outside for the same distance with the Leica total stations. This happens because in the field the total stations and consequently the measurements are influenced by the environmental conditions that are altered. • The Topcon instruments present steadily high percentage of the returned radiation for the distance of 15m and 50m indoors and for the distance of 50m outdoors. • Indoors (tunnel) at the distance of 50m, the percentage of the returned radiation for the Topcon total stations is 100% for all the materials apart from the self-adhesive glossy target and the glass, which have odd behaviour. • The Leica instruments express lower rates of returned radiation than the Topcon instruments for the same materials in the same angle. • At the long distance (200m) in the angle of 60° the results of certain materials was not satisfactory because the total stations could not measure by no means, due to the small percentage of the returned radiation. Thus the result cannot be properly evaluated. • At the distance of 50m outdoors, using the Leica total stations the percentage of the reflected radiation were satisfactory in all the angles for all the materials except for: o the self-adhesive glossy target o the black cardboard and o the glass • Light coloured objects reflect more radiation than dark coloured ones in the same distance. As the distance grows, this phenomenon is intensified. • Smooth surfaces reflect more radiation than the uneven, such as the asphalt and the rock. The effect of lighting of the room • The lighting of the room has small effect on the distance measurement. • In the dark, the percentage of the returned radiation is higher than with artificial lighting, using the total station Leica TCRM 1201 indoors at the distance of 50m. • Using the total station Leica TCRM 1201, at the distance of 50m indoors, without lighting, the 82% of the results were acceptable for confidence level 95%, while with artificial lighting the corresponding percentage was 79%. The reliability of the distance measurement • The more the material deviates from the perpendicular position to the laser beam, the bigger is the divergence of the measured distance on the reflector. • The bigger the distances are, the smaller the percentage of acceptable measurements for confidence level 95% becomes. • Indoors, at the same distance (50m), the acceptable measurements for the desirable precision are more than outdoors. • Outdoors, at the distance of 200m, low percentages of measurements are acceptable. For the total station Leica TCR 405: 23% For the total station Leica TCRM 1201: 18% For the total station GPT 3105N: 46% For the total station GPT 7003i: 28% For the total station Topcon GPT 3003LN, the percentage of acceptable results is 64% due to the use of the operation LNP (that has range up to 1200m), instead of the operation NP, which has a range up to 250m and hence less powerful radiation. Using the operation NP, only 20% of the results are acceptable. • Sometimes, the total stations could not measure on the selfadhesive glossy target due to its peculiar characteristics, at the 45° and the 60° angle, even in small distances. Even when the measurements were carried out, they were not acceptable. Consequently the self-adhesive glossy target should not be used in surveying works. • Using the white foam, the distance is overestimated. This happens in all the categories of instruments in all distances perhaps due to multiple reflections inside the material itself. The precision of the measurements • The measurements carried out by using the total station Topcon GPT 7003i, are characterised by stability, since the measurements to the same material at the same distance have divergences up to 5mm, except for the red plastic and the glass. • Outdoors, the measurements vary from 1mm to 9mm at the distance of 50m and from 1mm to 7mm at the distance of 200m for the same material at the same angle. • Indoors, the measurements vary from 0mm to 5mm whereas outdoors they vary from 1mm to 9mm at the same distance of 50m. The fluctuation outdoors is nearly double than indoors for the same distance. • Indoors, in the distance of 50m, the 48% of the measurements and in the 15m the 81% of the measurements has a dispersion up to 2mm (≤ 2 mm). • Outdoors, in the distance of 50m, the 29% of the measurements and in the 200m the 0% of the measurements has a dispersion up to 2mm (≤ 2 mm). Angle of incidence • The bigger the angle of incidence of the laser beam is, the less accurate the distance measurement is.