Base map revision using high resolution satellite data
Col. Somkiat Aisanont
Royal Thai Survey Department, Bangkok 10200, Thailand
Abstract
Maps are essential database for both planning and fieldwork operation. Up-to-date maps are necessary because obsolete maps cause users to be confused and create problems during work.
The conventional methods of map revision with aerial photographs are so costly and highly time-consuming that base map revision cycle cannot be done as planned. However, the recent availability of high resolution satellite data such as SPOT offer an interesting alternative for map producing and updating. The Royal Thai Survey Department, which is responsible for the production of topographic base maps for both military and general purposes realizes the usefulness of satellite data, hence initiating this project.
The objective of the project was to update base maps using SPOT imagery, Project area covered 24 map sheets of 1:50,000 located in the Central plain where it is dominantly flat terrain. SPOT panchromatic level 2 images were used, as main data source to add new information or changes of features on the base maps and multispectral level 1B were provided as supplementary information. Topographic base maps at 1:50,000 and 1:250,000 scales were simultaneously revised using optical transfer device.
Introduction
The Topographic maps which cover the whole area of Thailand are at the scales of 1:50,000 and 1:250,000. The latter series was derived from the first one.
The series of 1:50,000 which has been used widely, comprises 130 map sheets for the whole country. This series was mostly produced in 1969 and only some map sheets have been revised.
The Central plain Area is predominantly a flat terrain and has been developed rapidly which causes the map to be out of date. The Royal Thai Survey Department-RTSD is responsible for topographic mp production, revision and provision for both military and civil supposes. With a view to find an appropriate technique for map revision, the department has therefore put an effort in conducting the zloty project using satellite imagery for map revision. The high-resolution satellite images used for such purpose are available from the Thailand Ground Receiving Station, which has high capability in creiving Landsat TM, SPOT and MOS-1 data.
Objectives
- This project aims at using high resolution satellite imagery for updating and adding new features on to base maps at the scale of 1:50,000. A total of 24 map sheets will be updated and printed for non - permanent use.
- The products of item 1 will then be used for map revision at the scale of 1:250,000.
- The updated maps can be utilized as an input for other cartographic purposes.
Target Area
The target area of the project was selected by the RTSD Committee. The location of the area is in the Central Plain of Thailand where map details have been so much changed. It corresponds to sheets no. ND 47-7 of 1:250,000 scale and covers a total of 24 map sheets of 1:50,000 scale which are 4837 I, II, III Iv 4838 I, II, III, IV 4937 I, II, III, IV 4938 I, II, III, IV 5037 I, II, III, IV and 5038 I , II, III, IV.
Methodology
Several methods have been available for map revision. One should also take into account the development trends of this technology so as to choose a proper means suitable for the existing mapping system that one currently has.
