Does offer to download elevation files first check if those files exist or are out of date

Andrew Heard shared this question 7 months ago
Answered

During a recent map download Locus offered to download elevation data as below:

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Before tapping DOWNLOAD I checked the number/ size/ modified date of the SRTM HGT files. After the download I again checked the files. I saw no change to the existing HGT files. Does Locus first check if (any) existing HGT files are out of date? Otherwise this download may be a waste of time.


Some of the existing files were high resolution OpenDataPortal files (25MB each) which fortunately were not overwritten by lower resolution Locus files (2.8MB each).

Comments (5)

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Hello Andrew,

there is no check on "out of date" areas, there is only check on coverage. So if there are areas for which does not exists HGT files, this "download" is offered.

I do not know what exactly happen in your device, so cannot help here. I'm anyway not aware of any issue. Maybe hgt files were downloaded somewhere on SD card while you checked "data/srtm" directory in internal memory? Was there any progress during downloading btw?

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I am using the default SRTM folder. Yes there was progress during the download. So I did another test to determine why some SRTM files were missing:

  • deleted all HGT files
  • store > Italy > download elevation data - ~86MB
  • notification center now says all OK
  • exited, note 88 HGT files
  • re-run Locus
  • store > Italy > download elevation data - now says ~7MB (suggesting not all were downloaded although no previous error displayed)
  • notification center now says 8 more files to download
  • all appeared OK (now 96 files)
  • exit/ re-run Locus
  • now Locus says "required elevation already downloaded"


So it seems Locus didn't report that some HGT files weren't downloaded?

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Really interesting.

I've tried your method twice and in both cases, Locus reported need to download 86 MB files and after first step really downloaded necessary 96 HGT files.


I've already get bugreport on some problems with HGT download twice during last few months, but unfortunately I was not able to simulate it on own device.


So issue here is not incorrect check on existing files, but some problem with downloading.


I'll try it on more devices, if same issue appear. Thanks for now.

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Good to know at least one other person has had same problem ;-) Not just my imagination. Only Italy had download issues. I have since downloaded Austria & Switzerland, each time deleting the SRTM folder so I could 100% check for any problems, but all went well. Is the HGT download compressed? I couldn't think otherwise why 96 files x 2.75MB = 264MB, not 86MB.

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I've tried it on two more devices and no problem so far, hmm.


And yes, data are compressed.

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