MODIS Collection 5 Active Fire Product User's Guide Version ... - FAO

Inverse MappingHere we are given the row (i) and column (j) in MODIS tile H, V . First compute the position ofthe center of the grid cell on the global sinusoidal grid:x = (j + 0.5)w + HT + x min (7)y = y max − (i + 0.5)w − V T (8)Next compute the latitude φ and longitude λ at the center of the grid cell (in radians):Applicability to 250-m and 500-m MODIS Productsφ = y (9)Rxλ =R cos φ . (10)With the following minor changes the above formulas are also applicable to the higher resolution250-m and 500-m MODIS tiled sinusoidal products.250-m grid: Set w = T/4800 = 231.65635826 m, the actual size of a “250-m” MODIS sinusoidalgrid cell. For 250-m grid cells 0 ≤ i ≤ 4799 and 0 ≤ j ≤ 4799.500-m grid: Set w = T/2400 = 463.31271653 m, the actual size of a “500-m” MODIS sinusoidalgrid cell. For 500-m grid cells 0 ≤ i ≤ 2399 and 0 ≤ j ≤ 2399.4.2.7 Example CodeExample 2: MATLAB code to read the Level 3 MODIS daily fire mask, using the MATLAB routinehdfread. This is probably the easiest way to read individual HDF SDSs in MATLAB.mod14a1_file = ’MOD14A1.A2008281.h31v10.005.2008292070548.hdf’% read entire "FireMask" SDS in one shotfire_mask = hdfread(mod14a1_file, ’FireMask’);% display fire mask for the first day in MOD14A1/MYD14A1% note how image is transposed so that North appears on topimagesc(fire_mask(:,:,1)’);25