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Results of Encrypted Control Survey in Taichung City

  • Date: 2018-02-15
  • Issued by: Land Administration Bureau

A. Legal Basis

Item 1 of Article 5 of Land Surveying and Mapping Act and Article 29 of Enforcement Rules for Basic Survey. 

B. Origin and Background

According to Item 1 of Article 5 of Land Surveying and Mapping Act, this Land Administration Bureau is responsible for the planning, implementation and management of the encrypted control surveying tasks in Taichung City.Moreover, the Article 29 of Enforcement Rules for Basic Survey stipulates that the concerned local authorities should plan and implement the encrypted control survey regularly in its jurisdiction.

Before the merger of former Taichung County into Taichung City, the satellite tracking base station was already set up, in which the Coordinate Reference System was equipped to provide cadastral surveys for land development projects in the jurisdiction. It was tested to find that the cadastral surveys are very accurate with a tolerance within 2 centimeters. The Land Administration Bureau further expanded and renewed the Coordinate Reference System in 2012-2013 to serve as a basis for cadastral surveys and their subsequent surveying and mapping tasks.

The new Coordinate Reference System has 10 stations, each of which is over 20 km away from the next station on the average. As the distance and density were below the requirement for applied survey, the Land Administration Bureau decided to set up more encrypted control points in the jurisdiction of Taichung City to meet the need for applied survey.

C. Plan contents

(A) The setup of new Coordinate Reference System in greater Taichung area

In 2012 and 2013, the Land Administration Bureau set up 10 satellite tracking base stations, which were evenly distributed in the jurisdiction of Taichung and along the borders to the adjoining counties and cities. The stations can work together to measure and calculate the high-level control points to buildup the Coordinate Reference System in greater Taichung area.

(B) Draft the Encrypted Control Survey Operations Manual

Item 2 of Article 4 of Enforcement Rules for Basic Survey stipulates that the local authorities shall draft the specifications or the manual for encrypted control surveys and carry out the tasks in accordance with the written documents.

(C) Checks on permanent survey marks. 

According to Article 14 of Land Surveying and Mapping Act, local government authorities are responsible for maintaining the illustrated guides and carry out the on-site verification of the locations at a regular basis and record the most current status of the permanent survey marks. If the permanent survey marks are damaged or moved, such damages or unexpected movements should be reported to the central authority concerned. Moreover, Article 7 of the Enforcement Rules of Land Surveying and Mapping Act stipulates that the concerned authorities of special municipalities and county (city) governments shall implement the regular on-site checks at least once a year. The central competent authorities (including Ministry of the Interior and its affiliated National Land Surveying and Mapping Center) have set up 446 control points (in classes A, B, and C) in the Taichung area, most of which do not fully comply with the standards of "permanent survey marks" as stipulated by Item 11 of Article 3 of Land Surveying and Mapping Act, but this Land Administration Bureau has checked, maintained, recorded and reported all of their damage or relocation to the central competent authorities in the past and will continue to do so in the future. To preserve those encrypted control points set up under this plan, this Land Administration Bureau will build them as permanent survey marks according to Item 11 of Article 3 of Land Surveying and Mapping Act and Article 2 of Enforcement Rules for Land Surveying and Mapping Act.

(D) The first-stage density program: Class A encrypted control survey work

The Enforcement Rules for Basic Survey does not regulate the distance between one encrypted control point and the next point. However, considering that the results of the encrypted control survey shall be used in the applied survey, we decide to plan the distribution and density of the encrypted control points so as to meet the needs of traverse networks (Two adjacent points should be visible to each other.)

(E) The second-stage density program: Class B encrypted control survey work

With reference to the Implementation Rules for Cadastral Survey (before its amendment), we intend to put two adjacent class B encrypted control points at a distance between 0.5 and 1.5 kilometers. At the moment, we do not have the manpower, time and funds to carry out class B encrypted control survey work and the results from class A encrypted control survey work have met the needs of applied survey. Considering that there is no urgent need for full-scale class B encrypted control survey in the near future, we will therefore postpone the class B encrypted control survey work until when cadastral maps of the city will be re-drawn, or when the cadastral plan will be made for land development projects, or when other bureaus or agencies will carry out an applied survey project up to a certain size and conditions. 

(F) Announcement and management of results

The results and items of encrypted control survey shall be announced and reported to the relevant agencies (such as the Research, Development and Evaluation Commission and the Information Bureau of Taichung City Government), according to Item 2of Article 15 of Land Surveying and Mapping Act.(This also applies to the revisions).

D. Territory

This plan is executed within the jurisdiction of Taichung City.

E. Plan objectives

The main objectives are to plan the procedure and schedule for encrypted control survey in greater Taichung area, to establish the encrypted control survey results, to provide the results for the use in applied survey, and to unify the survey results under the same Coordinate Reference System.

F. Expected benefits

The results of encrypted control survey can be used in the applied survey and all the surveying tasks are conducted under the same Coordinate Reference System, so as to maintain the accuracy of the outcome, serve as the basis to establish a complete data bank for national soils, and provide the geographic information for direct GIS overlay to support the municipal construction decisions.

G. Results

(1) Class A encrypted control points within the jurisdiction of Taichung City were completed in 2012 and 2013 and survey operations for 318 classes A, B, and C satellite control points and satellite tracking stations were done.

(2) 164 encrypted control points have been set up and tested (22 of which use the same control points as class Csatellite points) and 4 old observation stations for satellite signals and 7084 new coordinates results for class A benchmark points have been calculated.

  • Date : 2015-09-02
  • Hit: 81
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