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Geoinformatics_05-2009
article figure 4 general overview of the campinas county orthomosaic in normal color. figure 5 general overview of the campinas county orthomosaic in false color infrared. dent wv-1 image, and figure 3 a 3d fragment of the dtm with contour lines. general results obtained for the dtm with no ground control at all and verified with 37 independent geodetic points resulted in a root means square (rms) error of 1.0m and final vertical accuracy of 1.7m. a well distributed subset of 23 points resulted in a rms error of 0.6m and final vertical accuracy of 1.0m. contour lines were derived with a resolution of 1.6m. a wv-1 orthomosaic was generated as an intermediate product to the final orthomosaic. the final orthomosaic, with the imagery already pansharpened, was then generated using autosync, an erdas product, collecting hundreds of tie points. figure 4 presents the general overview of the final orthomosaic in normal color and figure 5 in false color infrared. since the final archive size is of the order of 15 gb the final delivery was also in tiles according to brazilian cartography standards. the tiling grid is presented in figure 6. the final orthomosaic for the county of campinas presents a high image quality with excellent contrast, as in figure 7 normal color and figure 8 false color infrared. in order to perform the error and accuracy check a set of 80 independent geodetic points was used. the points are from the official county of campinas geodetic network (pmc) and were implemented by well known specialized companies. figure 10 presents the distribution of the geodetic points in the county. the points are mostly concentrated in and around the urban areas. this fact does not interfere in the objectives and results since the desired accuracy must be high in the urban areas and is not required in the rural parts of the county where the required result should be close to the scale of 1:5.000. final analysis for the rms errors and accuracy was performed comparing the coordinates of the 80 points set and the generated ikonos orthomosaic in wgs 84 and using the remote view software environment. remote view is well known to have an excellent graphic user interface (gui) and not blur the image; and in this work, since the error and accuracy checks are very close to the resolution of the imagery ( 1 pixel), this was a key issue. although the brazilian regulations state that in practical means wgs 84 is to be equal to sirgas 2000, it was observed that at this very high resolution level, conversions to and from different software platforms can introduce bias of the order of 0.5 to 1.0m. therefore, the analysis was performed exploring the remote view tools at a maximum and allowed for a grouping of the 80 points in 2 categories, i.e. 0.6m rms or lower (figure 14), and between 0.6m and 1m. 4. conclusions the county of campinas now has an updated high quality orthomosaic and also a very precise dtm. the final product compatible with the 1:2,000 nmas scale has proven to be perfectly adequate to the objectives and necessities of the gis campinas project. this gis is responsible for integrating the new generated cartography to the technical territorial & environmental cadastre of the county and to the databases and applications of all the organizations and secretaries of the county administration. besides generating a new territorial reference, the future yearly updating process and monitoring operations will be strongly facilitated and fostered, and possibly at an even faster pace. it is very important to clarify that the urban expansion process in the area is very fast and most times the velocity of the urban expansion is higher than the pace the county managers can see the territory and interfere; in other words: the urban expansion process has more velocity than control, and this is extremely undesirable since it does not allow, among others, to allow for assertive planning july/august 2009 figure 6 tiling of the campinas county orthomosaic. 24
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