4 ms·
> Something that is geographically notable but quite small, vertical and isolated (like Rockall) may very well also be omitted from that version of the EGPWS da
by roryisok 10y ago
> Something that is geographically notable but quite small, vertical and isolated (like Rockall) may very well also be omitted from that version of the EGPWS database.
Why are "small" and "isolated" good criteria for omitting something from a database of elevation geometry? It's evidently big enough to crash into and cause loss of life.
- theoh 10y agoI'm not suggesting that those are criteria, just possible contributing factors. (And I'm not trying to exonerate the suppliers. We'll see what the final report says.) If the source is some kind of DEM (digital elevation model) data, it will be a raster of elevation values at some limited resolution, so necessarily just samples of elevation. With a relatively small island/rock, the full height could be missed, and possibly then even further reduced by filtering (i.e. smoothing of DEM values, either in the process of measurement or some kind of processing). That likelihood is hinted at by this quote from the manufacturer: "Honeywell’s terrain data is sourced from our supplier [named supplier]. It is a digitized topographic map derived data set. It does not include Black Rock. We have looked at alternate sources, including SRTM and ASTER. While Black Rock is present in these alternate data sets, the actual altitude of Black Rock is considerably higher than what is indicated in these alternate data sets." The data sources they refer to: http://www2.jpl.nasa.gov/srtm/ http://www2.jpl.nasa.gov/srtm/ https://asterweb.jpl.nasa.gov/gdem.asp https://asterweb.jpl.nasa.gov/gdem.asp Again, not coming to any conclusions from this.