area2point.fix_geotiff_locations unexpectedly sets noDataValue=0

[asjohnston-asf]

This function is used by GAMMA RTC to translate all output rasters from pixel as area to pixel as point after RTC processing is completed: https://github.com/ASFHyP3/hyp3-gamma/blob/develop/hyp3_gamma/rtc/rtc_sentinel.py#L342

fix_geotiff_locations() overwrites any existing noDataValue and sets it to 0: https://github.com/ASFHyP3/hyp3-lib/blob/develop/hyp3lib/area2point.py#L33 .

This is a particular issue for DEM output files, which may have valid pixel values of zeros. For example, for an RTC image over death valley (S1A_IW_GRDH_1SDV_20201002T135151_20201002T135216_034618_0407ED_A3FB), the DEM packaged with the output has a clear ring of no data pixels where the terrain transitions from above sea level to below sea level. fix_geotiff_locations() should be modified to only convert from pixel as area to pixel as point, and any noDataValue business logic should reside elsewhere.

[rudigens]

Very good call, Andrew. I have thought about this issue for a while but could not come up with an efficient way how to fix it. Might want to have another discussion with everybody around about what our options are. The cleanest way would actually to fix this in the DEM tiles but it is a lot of work and not that trivial to get it right at the coastlines.

[talogan]

I agree this is an issue wherever we have land below sea level (ocean coasts). However, I'm not sure that we can fix this. Gamma's nodata value is 0. Wherever a DEM has a zero value, no terrain correction is performed and, instead, output pixels are set to zero. Thus if we have DEM values less than zero, we'll get a ring of nodata values at the transition from positive to negative as is evidenced in the Death Valley scene that Andrew processed.

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On Thu, Jan 14, 2021 at 9:34 PM Rudi Gens ***@***.***> wrote: Very good call, Andrew. I have thought about this issue for a while but could not come up with an efficient way how to fix it. Might want to have another discussion with everybody around about what our options are. The cleanest way would actually to fix this in the DEM tiles but it is a lot of work and not that trivial to get it right at the coastlines. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#232 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAP2NOJ2JVV5GZYD4QLZGTDSZ7OX3ANCNFSM4WDMBQUQ> .