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[mkgmap-dev] How to handle missing hgt files or files with voids?

From Gerd Petermann GPetermann_muenchen at hotmail.com on Mon Jan 15 07:45:48 GMT 2018

Hi all,

1) The current code (only) writes a log message with severity WARNING for a missing hgt file:
"file xxx.hgt not found. Is expected to cover sea."
I wonder if we can create a list of files that can exist or maybe a polygon that can be tested so that
tiles which are knwon to cover land are reported as errors.
When you look at http://viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm
you can see that such a polygon would be quite complex.
Did anybody already try to define such a polygon or list of files that would cover only ocean?

2) Should mkgmap print a warning when voids in the hgt file(s) have an influence on the DEM data?
I think yes, but it is a bit more complex to measure the real effect. 
Reason: We read the 4 hgt values next to the wanted DEM point and use interpolation to calculate the height
that is stored in the DEM file.
If one or two of the 4 points are voids they may still have no influence if the wanted point is very close to one that 
is not a void. Another problem is that a single void might be used several times.
So, another option would be to add an option like --dem-check-hgt which could read all existing hgt files and 
report the number of voids for each. I'd prefer this because it would have no impact on performance for normal 
processing. Or maybe there is already a tool for this that works on all platforms (win,linux,mac) ?



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