Pixels which are nearest to the satellite's pass track projection (dashed red line with "Flight direction" label) will stay (almost) untouched during rectification. After image rectification procedure we should get image with even pixel spacing so every pixel shift in image corresponds to the same distance shift in kilometers on Earth surface. This resolution should stay constant during satellite working cycle (I believe it's 4 km/px for NOAA and 1 km/px for Meteor-M series). So at every time moment $t_i$ we obtain a bunch of image lines, let's say that for time interval $\Delta t = t_-t_i$ we have four rows of pixels. It scans Earth surface and sends data as image lines with even interval. Let's take that satellite is passing from South to North at certain angle.
TLE USED BY WXTOIMG HOW TO
Here is my thoughts about how to perform pixel geotagging. Is it right approach? I think I can catch moment when satellite transmits image line for my latitude (may be derive it from TLE parameters) but I don't know how to find longitude.ĮDIT 1. My suggestion is to find one basis point/pixel on my image which is my ground station (GPS coordinates for ground station are always available) and then, knowing rectified image dimensions and resolution, I could draw geographical data (for example from GADM) in overlay.
Does APT suggests the same data or I should rely on exact computer time and updated TLE?Īnother problem is that I can't figure out (yet) how to bind together timestamp info, TLE data and get geographical data for pixels. The only thing that I found is that LRPT packets could contain APID 70 data which is satellite's onboard time. However I can't find very much info about APT/LRPT protocols. recorded with GQRX and then processes in Audacity) contains some timestamps (or may be GPS coordinates) and smart programs like WXtoIMG are possible to process this hidden metadata together with TLE data and draw geo objects in overlay.
TLE USED BY WXTOIMG SOFTWARE
The same functionality exists in WXtoIMG software and it works only if you have updated Keplers list.
More specifically I want to add possibility to overlay geographical data such as land borders, administrative borders, rivers etc on the resulting images after rectification. I want to extend functionality of some open-source programs which decode APT and LRPT images (wxapt and glrpt).
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