Spatial Database Layer Updation
Satellite images provide latest information about various land-cover types like roads, urban areas, canals, railway lines, forests, barren land etc. and hence they are very useful in updating the spatial data elements containing above information. This facility is especially of very much use when for a particular area; the information is obtained from the maps, which are more than 25 years old. The spatial database layer updation procedure could be used for updating a spatial data layer using the satellite data of the recent dates. The updation should not only include spatial part but its corresponding descriptive part also.
The layer updation process could consist of database layer selection for updation and image using which it is to be updated, performing screen management utilities required and carrying out feature editing actions and session management actions. For this purpose, an easy-to-use and menu-driven procedure should be developed and it should have the following facilities.
Layer Selection and Background Image Setup
The spatial database layer updation menu should offer choice of layer to be updated from the vailable spatial data layers and background image to be selected from the image catalogue.
Screen Management Utilities
The utilities for screen management should include displaying of the features having image in background, zooming the area of interest, displaying the full view and inquiring about the attribute of the selected feature.
Feature Editing Actions
The feature editing facilities should include adding a new point, line or polygon feature and its attribute, selecting a feature for editing operation, splitting a feature in to two parts, codifying a feature, removing a feature from the database and undoing the last delete operation.
Session Management Actions
Session management actions should provide facility for saving the updated layer in to the target database after performing necessary actions such as line or polygon topology building.
Image-map Generation
A spatial database contains information about variety of spatial elements. Often, it becomes very useful for the user to generate a hardcopy map containing spatial data elements such as roads, water bodies, administrative boundaries, important landmarks, features of special significance etc. with satellite image as a background. Such map plays an important role when the user wants to visit a particular site on the ground for the purpose of making ground truth. Such maps are also very useful to give a total picture of a study area. The Image-Map generation procedure should be developed to generate hardcopy maps for an area of interest with satellite image in the background over which other spatial database features are overlaid.
The Image-Map making should have the following steps.
- Selection of the area of interest from the entire spatial database.
- Extraction of the area of interest as a function of map-scale and paper size.
- Examination of the extracted area on screen by superimposing different spatial database layers on the selected image.
- Making map composition once the contents are finalized.
- Annotation of the map using map elements like text, box, circle, line etc.
- Creation of a plot-file for obtaining hard copy of the map.
Selection of the Area of Interest
The user should select the area of interest by clicking the point on the displayed image. Before selecting the area of interest, user should select appropriate image from the image catalogue. The selected image will appear in the background of the Image-Map.
Extraction of the Area of Interest
The size of the area of interest to be plotted depends upon the map scale and the paper size. After the map scale and paper size are selected, the system should determine the size of the area to be extracted around clicked point as a function of map scale and paper size and display only the extracted area on the screen in place of entire spatial database layer. The user should be able to change the map scale and paper size if required until the entire area is covered properly.
Examination of the Area of Interest
During this stage, the user should be able to select different options for superimposing various spatial elements from the spatial database on the background image. Facility should be provided to execute this step repeatedly until the user finally decides that which features should be drawn on the final Image-Map.
Making Map Composition
The extracted and examined area of interest should undergo map composing process in which all the image and spatial database map elements should be entered and finally marks showing distance in kilometers should be drawn on all four sides of the map. This map composition could be annotated and printed later on.
Annotation of Image-Map
This Image-Map should be annotated to increase its usefulness. The process of annotation may include writing the names of the places, putting the date of the background satellite image, writing the name of the area of interest, writing scale of the map etc. Facility should also be provided to put text strings of different size and colors at desired location on the Image-Map. Facilities for drawing circles, boxes, irregular polygons etc. with different colors and sizes are also provided.
Generation of Hard-copy
This step should ask the user about the format in which the plot-file is to be generated. The choice could be generating the plot-file in HPGL or Encapsulated Post-Script (EPS). The plot-file could be plotted using an operating system command.
Conclusions
The process of digital image integration into the spatial databases is described along with the two of its utilities namely spatial database layer updation using the images integrated with the database and preparation of the Image-Map containing spatial database features with image as background. Such utilities will be very much useful when NRIS spatial databases will be operationally used for the management of natural resources. Towards these, these concepts are being used for developing GIS based menu driven and easy to use command procedures called ‘Shells’. A prototype has already been developed and it will be offered for use after proper Test and Evaluation.
AcknowledgementsThe authors are thankful to Shri A.K.S. Gopalan, Director, SAC and Shri A.R. Dasgupta, Deputy Director, SIIPA for providing us the opportunity to work in this field and constant guidance and encouragement provided by them. The authors are also thankful to Shri I.C. Matieda, Shri Satishkumar, Shri Gogoi and Ms Sanjukta for their valuable contribution made for image downloading procedures.
References
- NRIS Node Design and Standards, Technical Note, SAC/SIIPA/NRIS-SIP/SD-02/98, July 1998.