Hi,everyone: I am now processing TRMM 1B11 data which has about 3000 scans per orbit and 104 observations per scan. So the DN array is always 3000*104. To build a glt for whole HDF is time-consuming, so I just want to build glt for my interested area. I know the line and sample in the HDF file. So I could extract the lat/lon for my interested areas and build the part glt. Then I apply it to the corresponding part DN, but results are all zero but geolocation is right. Later I apply the part glt to whole HDF, and result gets OK. However when I want to do it in envi routine, the envi_glt_doit does not give correct part glt compared to the envi software. They have about 30 pixels that does not match. I have checked the input to software and envi_glt_doit, they are both exactly the same. I do not know what is wrong with it. Is anyone has similar situation? Or anyone knows how to georeference part HDF using glt? Thank you very much!