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Poster Session
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Base map revision using high resolution satellite data
The methodology used in this project is an economical one and can be performed directly onto paper maps, which is the current forms of maps for Thailand, The updating is carried out by using an optical transfer device called Procom-2 as the following steps.
- Selection of maps and images
- it seems beneficial to update maps that have never been revised since the first edition. The type of terrain is also another important element. Flat terrain should be selected to preclude relief displacement. The target area of this project covers 24 map sheets of 1:50,000 (Table1) located in the flat terrain of the Central Plain. Information on the existing base maps was collected in 1969. Since one map sheet of 1:250,000 scales comprises 24 map sheets of 1:50,000 the updating of these 24 map sheets would then lead to updating of the 1:250,000 map sheet number RND 47-7.
- SPOT images, both Panchromatic Linear Array (PLA) and Multispectral Linear Array (MLA), in the form of positive films were used.
PLA images, which provide a resolution of 10 m X 10 m, were essentially used for interpretation and delineation of new features. Therefore, images of level 2 (Geocoded, precision corrected) were selected. Such images were also of vertical or near vertical viewing angle, cloud free and recent acquisition. The index of a total of 34 PLA level images used for updating is shown in Figure 1, which the details of original PLA images are shown in Table2.
MLA images which provide a resolution of 20 m x 20m were used as supplementary data for interpretation of some features like present forest boundary, encroachment area that has become agricultural Landuse of urban area, new water bodies such as irrigation canals, ponds, reservoirs, Therefore MLA images of level 1B (full scene, bulk corrected) were used and the details are shown in Table 3.
- Interpretation of SPOT images
Interpretation of SPOT images were conducted by using an article transfer device called PROCOM-2 . With the device, the image alas could be enlarged and projected on to 1:50,000 maps. Because of is zooming and roaming capabilities, the PROCOM-2 allows super imposition of the satellite image onto the map and working directly at the map scale.
Common features on the map and image such as roads, rivers, creams, ponds or reservoirs, etc. were used for local registration in such sub-area of the base map. All types of features were interpreted and drawn on the base map with pencil.
- Field verification
All features that were located onto the maps in the office are then checked in the field. The purposes of field work were to verify and classify the detail of new features such as type of roads (hard or loose surfaces), road number and width, type of agricultural and, names of features such as school, monastery, village, reservoir etc.
- Post field verification
The ambiguous features from interpretation in the office could be identified after field verification. Some features could not a detected by satellite images like important official buildings then were covered with tree crowns. Such features could be mapped fleld verification. Field verification is by all means necessary and very useful.
- Revision and colour separation of the originals
After field checks, the new features and changes were drawn overlays. These overlays were used for scribing on the scribing rats derived from the originals of existing base maps.
Colour separation was generated on positive films. All of the revised positive films were finally integrated to generate new negative originals for printing in the next step. However, before the process of printing, colour proof had to be performed to check for me errors.
- Colour separation for 1:250,000 map compilation
After 24 map sheets at the scale of 1:50,000 were updated, of the revised originals were transferred to 1:250,000 scale.
- Printing
- A total of 24 updated maps at 1:50,000 scale wee printed the standard legend. The remark non-permanent use is shown on top the sheet. Lower left corner denotes Updated for all major sturesusing SPOT satellite imagery otained in.........
- One sheet of updated map at 1:250, 000 scale was printed is sheet number is ND 47-7.
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