Geoidi mudeli EST-GEOID2017 täpsuse analüüs Tartu linnas
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Kuupäev
2019
Kättesaadav alates
12.09.2019
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Eesti Maaülikool
Abstrakt
Käesolevas töös on uuritud Eesti geoidi mudeli EST-GEOID2017 täpsust ja nihet Tartu
linnas, mis on ka antud töö eesmärk. Aina enam kasutatakse tänapäeval mõõdistamise
meetodit RTK pluss geoid, kuna see on tunduvalt kiirem, lihtsam ja odavam kui
nivelleerimine. Seega on geoidi mudeli täpsus väga aktuaalne teema. RTK meetodil
mõõdistades saame kõrgused ellipsoidilt ning seejärel tuleb neid parandada geoidi
mudeliga.
Kuna Eesti läks üle Amsterdami nullile 1. jaanuaril 2018, siis hakkas kehtima ka uus
kõrgussüsteem EH2000. 2018. aasta algusest kasutame uut ja täpsemat geoidi mudelit
EST-GEOID2017, mida järgnev töö analüüsib.
Töö meetodiks on võrrelda GPS mõõdistamis- ja nivelleerimisandmetest arvutatud
geomeetrilist geoidi Eestis kehtiva geoidi mudeliga (gravimeetria põhine sobitatud
mudel), et tuvastada nii täpsust kui ka süstemaatilist nihet.
Lähteandmetena on kasutatud Tartu linna kohaliku võrgu 1. järgu punkte (29), riigi
geodeetilise võrgu II klassi punkti Lemmatsi97, Tartu lähedasi tihendusvõrgu punkte (6),
kuna neil on kõige täpsem geodeetiline kõrgus. Samadele punktidele on määratud ka
normaalkõrgus kas geomeetrilise- või trigonomeetrilise nivelleerimisega, ning analüüs
mõlemale meetodile on tehtud eraldi.
Töö käigus selgus täpseimate punktide (14) põhjal, et mudelis EST-GEOID2017 on Tartu
linna kohal minimaalne süstemaatiline nihe (1,3 mm), keskmine ruutviga tuli 5,1 mm.
Sama nihet analüüsiti ka trigonomeetriliselt nivelleeritud punktide (20) abil ja saadi
tulemuseks 3,5 mm, keskmine ruutviga tuli 8,8 mm. Tulemustest näeme, et Tartu linnas
pole vajalik süstemaatilist nihet rakendada, samas saame väita, et geoidi täpsus Tartus on
väga hea ja sarnaneb üleriiklikult deklareerituga (5 mm).
The aim of this paper is to examine the accuracy of the EST-GEOID2017 geoid model in Tartu, Estonia. GNSS levelling combined with geoid model has become a widely used method for land surveying. GNSS – levelling gives us an elevation measurement from the mathematical ellipsoid of the earth. To convert the ellipsoidal heights to normal heights, a geoid model is essential. The main factors, that support the use of GNSS-levelling, is the fact that it is faster, cheaper and easy to use than usual levelling. After the transition to the European Vertical Reference System on 1st January 2018, a new system EH2000 of normal heights was declared. Therefore, since 2018, Estonia is using a new and more precise geoid model named EST-GEOID2017. The method used in this paper is to compare geometrical geoid heights against model ESTGEOID2017 (this is gravity based and fitted model), to detect the accuracy and systematical deviation. I order points from Tartu local geodetic network, II order point from state networks called as Lemmatsi97 and some points from densification network have been used for the evaluation process. A normal height determined to these points comes from geometric levelling or trigonometrical levelling and is analyzed separately. As a result, this thesis detects a systematical shift of only 1,3 mm on model Est-Geoid2017 and mean squared error of 5,1 mm on the research points (based to 14 most accurate points). This deviation was analyzed with 20 points by trigonometric levelling too and the results were 3,5 mm systematical deviation and 8,8 mm mean squared error. On this basis, we conclude that EST-GEOID2017 is within the declared accuracy of 5 mm in Tartu. Therefore there is no need for accounting the systematical error in GNSS levelling.
The aim of this paper is to examine the accuracy of the EST-GEOID2017 geoid model in Tartu, Estonia. GNSS levelling combined with geoid model has become a widely used method for land surveying. GNSS – levelling gives us an elevation measurement from the mathematical ellipsoid of the earth. To convert the ellipsoidal heights to normal heights, a geoid model is essential. The main factors, that support the use of GNSS-levelling, is the fact that it is faster, cheaper and easy to use than usual levelling. After the transition to the European Vertical Reference System on 1st January 2018, a new system EH2000 of normal heights was declared. Therefore, since 2018, Estonia is using a new and more precise geoid model named EST-GEOID2017. The method used in this paper is to compare geometrical geoid heights against model ESTGEOID2017 (this is gravity based and fitted model), to detect the accuracy and systematical deviation. I order points from Tartu local geodetic network, II order point from state networks called as Lemmatsi97 and some points from densification network have been used for the evaluation process. A normal height determined to these points comes from geometric levelling or trigonometrical levelling and is analyzed separately. As a result, this thesis detects a systematical shift of only 1,3 mm on model Est-Geoid2017 and mean squared error of 5,1 mm on the research points (based to 14 most accurate points). This deviation was analyzed with 20 points by trigonometric levelling too and the results were 3,5 mm systematical deviation and 8,8 mm mean squared error. On this basis, we conclude that EST-GEOID2017 is within the declared accuracy of 5 mm in Tartu. Therefore there is no need for accounting the systematical error in GNSS levelling.
Kirjeldus
Magistritöö
Geodeesia ja maakorralduse õppekaval
Märksõnad
magistritööd, geoid, geodeetilised süsteemid, mõõdistamine