Re: Maps

Fred Hillhouse

I looked briefly at Terrain Navigator. It looks like it uses the USGS Topo, satellite imagery plus another 60 or so sources. In almost every case when a product uses a wide variety, they commonly use available sources such as OSM and ArcGIS. They may save the data as tiles or use a database format. If they use tiles then you can find them and very likely point APRSIS32 at them, otherwise they can’t be used. Look around your hard drive and you should be able to find the files. They could be sizable.


I don’t see the number of tiles or the space they require to be much of an issue these days unless you need terrabytes of data. With the advent of cheap large capacity drives you can fit a lot of tiles. Even the uSD cards hold a lot and they are getting cheaper every day. It would be easy to set up an uSD for Montana and another for Idaho. For my tablet, I run APRSIS32 on a 64GB microSD card. It works very well and I have several tile sets.



One way to limit the numbers of tiles downloaded is to limit the maximum zoom level for a tile set. You can even set to minimum but there is little space or quantity advantages. Quite a few tile sets only have tiles to level 15 or 16. If you set to the limit to that number it won’t try to download the next level all the time and when you zoom in, the lower level zoom will be used. If you look closely at the various level of tiles it becomes apparent the same scan was used for several level. For instance, for USGS a 7.5min map was scanned and then the scan was cut up into appropriate zoom levels. There is no new data, just a larger or small view of the data. For OSM tiles, there is new data at some of the very highest zooms. But I find while travelling I don’t need to see house shapes and swimming pools. I can avoid the highest levels in OSM too. I do find level 15 to be about the maximum I need as it is the level where street names are added. Aerials are a different story. For those I tend to want to higher zoom at least when using ArcGIS World Imagery: their level 18 is high resolution. They don’t have higher than 18 though.


There is also a common misconception that every tile at every zoom level and for the whole area is required. That is rarely true. Of course I don’t know your particular travel plans but it is unlikely they include every square mile and much of that may be just getting for one stopping point to another. By limiting your focus you may find there is a nice level that will please you. I used to travel between Arkansas and New Hampshire every few months. My total number of tiles and the space required never really added up to much.


One disadvantage of using a database for tiles is if the file is corrupted, you may lose access to all maps. In one application I looked at, I am pretty sure they managed two files. It looked like one file was used to point to a specific record within the second one. If either file is corrupted, then both are unusable. Not so with tiles since each is its own entity.


Best regards,

Fred N7FMH



From: aprsisce@... [mailto:aprsisce@...]
Sent: Sunday, March 26, 2017 11:34 PM
To: aprsisce@...
Subject: [aprsisce] Maps



Any way to configure this program to access maps I already own from terrain navigator?? They are awesome high res maps and I have the rights to print and edit for personal use. So allowing aprsisce to access the file shouldn't be a legal issue.
Basically I spend 8 months a
Year traveling the western usa and even though it's a heap of data I need massive amounts of map tiles.

Matthew KK6WBY

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