METODE PENCUPLIKAN NILAI ECHO CITRA RADAR *.PNG DENGAN REFERENSI SPASIAL DAN KOMBINASI WARNA RGB
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Abstract
Intisari
Data meteorologi yang berupa citra/gambar sulit dianalisis dan dikombinasikan dengan data lain. Dalam tulisan ini akan dijelaskan metode pencuplikan citra/gambar radar yang dipublikasikan oleh BMKG menjadi data teks. Proses pengolahan terdiri dari dua tahap yaitu proses pemetaan setiap pixel dalam citra radar menjadi koordinat bumi (latitude dan longitude) dan penentuan nilai echo radar (dBZ). Dari legenda pada citra radar didapatkan 9 pola warna RGB yang digunakan sebagai penentu nilai dBZ setiap pixel dalam citra radar. Hasil pengolahan citra radar berupa data teks yang terdiri dari longitude, latitude, dan nilai dBZ. Untuk membandingkan dengan data asli, data radar teks hasil pengolahan ditampilkan pada Website Global Informasion System (WebGIS). Warna data radar pada WebGIS ditentukan dengan persamaan warna sebagai fungsi dari nilai dBZ. Secara kualitatif, hasil perbandingan gambar radar asli dengan data numerik yang ditampilkan pada WebGIS menunjukkan bahwa hasil data numerik cukup presisi pada posisi longitude dan latitude. Namun, dari segi nilai numerik echo radar (dBZ) yang dihasilkan terdeteksi kurang akurat pada batas awan karena latar belakang gambar yang berwarna hitam.
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Abstract
Meteorological data in the form of image has difficulty in further analysis such as to combine the data with other data sources. In this research, the proposed method for converting image data into texts using image processing for BMKG data provided is presented. The processing scenarios consist of two main steps; mapping process of every pixel of the images into the earth coordinate (latitude and longitude) step and radar echo values estimation in dBZ step. From the analysis, the 9 color patterns of RGB are obtained and used as the dBZ justification tool for the pixel color of radar image. The results of this image processing step are the texts data of latitude, longitude and the radar echo values in dBZ. In order to compare the analysis results with the original data, the processing data are then reshown to global information system website (WebGIS). The radar color data on WebGIS is determined based on color equation as a function of the echo radar. Qualitatively, the results of this comparison show that the numerical data results are precise in terms of longitude and latitude positions. However, in terms of numerical values echo radar (dBZ), the results perform less accurate especially on the boundary of the cloud due to the black color of background image.
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