APRS-IS32 entire region prefetch problem
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Wojtek Jakieła
Hi!
I've been trying to figure this out since the morning, but I'm a bit overwhelmed and I'm need on your help. I use OpenStreetMap, ThunderForest and Google Maps in APRS-IS32. I need to download an offline area of the entire subcarpatia region in Poland (in 99% of places in my area where I try to do various experiments, there is no GSM coverage to run the Internet). APRS-IS32's built-in prefetch function allows you to capture only a small range of magnification. And also I never know in which terrain and when I will land in order to prepare maps in advance. I would need to download a zoom range from 9 to 19. Yes I know it will weigh a lot and take a long time. But is there any free way to download it? Thank you in advance for your help! |
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Rob Giuliano
Have you read the info on the wiki? http://aprsisce.wikidot.com/map-prefetch The author (Lynn) has suggestions on how to get maps. Robert Giuliano
On Sunday, February 19, 2023 at 09:59:48 AM EST, Wojtek Jakieła <wojtekjakiela@...> wrote:
Hi! I've been trying to figure this out since the morning, but I'm a bit overwhelmed and I'm need on your help. I use OpenStreetMap, ThunderForest and Google Maps in APRS-IS32. I need to download an offline area of the entire subcarpatia region in Poland (in 99% of places in my area where I try to do various experiments, there is no GSM coverage to run the Internet). APRS-IS32's built-in prefetch function allows you to capture only a small range of magnification. And also I never know in which terrain and when I will land in order to prepare maps in advance. I would need to download a zoom range from 9 to 19. Yes I know it will weigh a lot and take a long time. But is there any free way to download it? Thank you in advance for your help! |
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Wojtek Jakieła
Yes i readed.
But i need to download entire area of subcarpathia in Poland. |
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Lynn Deffenbaugh
For the reasons described on the Wiki, that's all the prefetch options that APRSIS32 supports. And I really question your need for zoom level 19 across a large area. That's more tiles, I think, than you are imagining. Even zoom 16, 17, and 18 over that large of an area is a really large set of files. You may want to look into running your own local tile server so that it can create the actually needed tiles on-the-fly and only when needed. It's not that resource intensive to set up a tile server for a country or subset of a country. It's only entire planet coverage tile servers that are resource intensive. https://switch2osm.org/serving-tiles/ uses azerbaijan as the
example, but Poland would work just as well. But a tile server
will require Ubuntu or other *nix variant. I would not suggest
trying to get all of those piece/parts working on Windows. Lynn (D) - KJ4ERJ - Author of APRSISCE
for Windows Mobile and Win32
On 2/20/2023 3:27 PM, Wojtek Jakieła
wrote:
Yes i readed. |
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Lynn Deffenbaugh
Województwo podkarpackie (Subcarpathian Voivodeship) is only a 111 MB download for the original OSM data. https://download.geofabrik.de/europe/poland.html Lynn (D) - KJ4ERJ - Author of APRSISCE
for Windows Mobile and Win32
On 2/20/2023 3:53 PM, Lynn Deffenbaugh
wrote:
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James Ewen
>Województwo podkarpackie (Subcarpathian Voivodeship) is only a 111 MB download for the original OSM data. Lynn, for illustrative purposes, could you estimate the storage necessary to hold all of the rendered tiles at all zoom levels for this same area? I don't believe that many people understand the sheer size of all the rendered tiles. James VE6SRV |
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James Ewen
Let me answer my own question... I just found a new toy! You'll need 19 GB of file storage for all zoom levels down to 18. I think you'll need another 48 GB of storage for zoom level 19 if I can do math properly. If you are using these offline maps for something like ARHAB balloon recovery, or similar, you might find that the extreme zoom level maps contain very little extra information than the tiles a couple levels up. There are very few areas where information on every blade of grass, and bit of gravel are mapped. The precision of the data in the OSM database is no where good enough to have these extreme zoom levels provide much useful information. Maybe take some time to run through your process (whatever it is you are trying to do offline), and have a look specifically to see if the tightest zoom levels are actually required. When I started playing with OSM I wanted similar offline maps for the province of Alberta in Canada. 228 GB is a hefty chunk. I found that I really didn't need anything closer than zoom level 14. Looking at your area, by the time you get to zoom level 15, you already have house footprints, and just about all of the information that can be seen. Zoom level 16 has bus stops, and zoom level 17 puts addresses on houses. I'm not sure what more information might be found on zoom 18 and 19. (I just found some park benches and garbage cans at zoom level 19) I guess there is an argument that can be made for needing very tight zoom tiles, but generally very detailed work doesn't happen on a large scale area all at once. James VE6SRV
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Lynn Deffenbaugh
While James was locating that cool tool, I was taking a different approach the results of which are in the attached Excel sheet. I took the .poly file from the following URL, found the min and max lat and lon and then plugged in the tile X/Y calculations from the second URL and then multiplied the delta tile numbers together to get the total tile count per zoom level. My results are higher than the geofabrik tool, but only to the tile count, not the anticipated space consumed. 29,829,949 Total Tiles Dropping zoom 19 leaves 7,465,346 which
is almost double what the Gofabrik tool shows. But if you read
their caveat, they only counted the tiles on their server. If a
particular map are has never been visited, they won't even have
that rendered tile to count. But if you download everything
within that bounding box, you'll get my numbers. 19 - 22,364,600 18 - 5,595,993 17 - 1,400,377 16 - 350,784 15 - 88,218 14 - 22,270 13 - 5,676 12 - 1,452 11 - 408 10 - 102 9 - 36 8 - 15 As James suggested, actually look
critically at the map at the various zoom levels and you'll likely
find that you really don't need much beyond 15 or 16 which, as you
can see above, drastically reduces the tile file count.
But I hope you begin to understand why
it's never a good idea to want to preload a large area of tiles.
The load on the tile server is EXTREME in rendering all of those
tiles, most of which will NEVER be viewed.
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32 On 2/21/2023 11:00 AM, James Ewen
wrote:
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James Ewen
Hmm, I missed the caveat on that site... I thought it was just doing the calculation based on bounding box like you did in Excel. It says there's only 5.6 million tiles total for that area down to zoom level 18. You show 5.6 million tiles just for zoom level 18. On the page that sent me to the tile estimator, they suggested each tile on average is 633 bytes. Any way you count it, it's a lot of tiles, and a lot of storage space. James VE6SRV On Tue, Feb 21, 2023 at 9:28 AM Lynn Deffenbaugh <kj4erj@...> wrote:
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Wojtek Jakieła
In general, even 100GB is not a problem for me.
We help during the search for missing people in small villages, in fields and forests using APRS.
We follow the moving cavalcade, so we need the greatest possible approximation (the cavalcade is 100-200m wide).
We help throughout the Podkarpacie region, sometimes we go to action without even knowing where we are going (in many places there is no GSM and Internet). We learn about it in fact while driving with the fire brigade or the police.
That's why we need our entire region with the best possible magnification. |
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