The tides in the western sea of Taiwan Island are mainly affected by Pacific astronomical tide and shallow water effect in Taiwan Strait. The significant tidal variation has resulted in significant difference in tidal hours and tidal levels of near shore and offshore areas. The survey range of the Taiwan base chart covers near shore, territorial sea, and adjacent sea areas. During sounding, the tidal correction of sounding data is based on the citation of tide observation data of the nearest tidal station, which will result in the error of near shore and outer sea depth sounding data and impact the accuracy of bathymetric survey.
The difference between the near shore tides and offshore tides of Taiwan western sea and established Tidal Zone as the basis for bathymetric survey correction mode has been analyzed by NLSC. The accuracy of this mode has been verified by the observation of the GPS buoy in order to effectively improve the accuracy of bathymetric.

Geoid is a hypothetical surface, which means it is an equipotential surface of actual gravity field of the Earth. The height obtained by leveling survey is called orthometric height (with Geoid as the reference), and the height obtained from satellite observation is called ellipsoidal height (with Spheroid as the reference). The difference between the aforementioned height systems is called geoidal undulation (N value). Once the accurate geoidal undulation value at any location obtained, it offers high accuracy conversion between ellipsoidal height and orthometric height.
MOI and NLSC have been actively promoting and performed a series of the gravity surveys in Taiwan, where terrestrial gravity survey, airborne gravity survey, and shipborne gravity survey have been arranged by overcoming the particular geographical environment of Taiwan in order to establish a complete gravity network. In addition, the 2014 Taiwan Geoidal Undulation Model has been established for people from all fields in coordination with high precision Digital Terrain Model (DTM), satellite survey of first order level points, and correction of observation data of leveling survey.

The checking survey, management and maintenance of basic control points in Taiwan with TWD97 [2010] coordinate results has been conducted in coordination with the TWD97 [2010] results announced by MOI on March 30, 2012. The checking survey data over the years have been used to carry out the operation of “Establishment of Modern TWD97 National Coordinate System Movement Mode”, in which the prototype of TWD97 coordinate system movement mode has been established by analyzing the impacts of tectonic plate movement on the displacements of basic control points. The basic control points checking survey will continually be carried out in the future with the results of satellites of various agencies and continuous observation stations included into the calculation and analysis in order to establish a more complete and sophisticated modern TWD97 coordinate system movement mode.

Prototype of Taiwan TWD97 National Coordinate System Movement Mode

The purpose of the project is to build the mobile mapping system which can not only assist to update the data, but also improve efficiency of acquisition and analysis spatial data. The structure adjustment, assembling, and testing of mobile mapping system and monitoring software had completed in 2015. In 2016 and 2017, there are 218 kilometers including 40 new construction areas of Taiwan e-Map updating by using mobile mapping system. We also try to test the personal mobile mapping system. Following 2017 and 2018 will develop Lidar mobile mapping system technology and point cloud data processing mode.

Mobile Mapping System of NLSC

To establish a credible calibration field is the first step to promote calibration system for aerial photogrammetric camera. Starting from 2009, the NLSC successfully established the calibration field for aerial photogrammetric camera at the Nankang Industrial Park, Nantou County in 2014. It contains an inner field with the size of 750X600 m for cameras flying lower altitude to be used for larger scale map production, and an outer one with the size of 2000X1750 m for higher altitude and smaller scale map missions. The NLSC has built fixed-type marks for geometric calibration in this field totally 183 marks, and 2 sets of mobile marks for spatial resolution and radiation calibration. This field has been verified in 2016 by the Taiwan Accreditation Foundation (TAF) its effectiveness of the calibration procedures which accords with ISO 17025.

Maintenance of geometric calibration marks distributed averagely
in photogrammetry camera calibration field

National Land Surveying and Mapping Center. Republic of China(Taiwan)National Land Surveying and Mapping Center. Republic of China(Taiwan)

Achievements