SarTopo Offline Use / Map Sharing

Christopher Mears's Avatar

Christopher Mears

19 Nov, 2021 04:20 PM


I am seeking information on how to exchange SARtopo mapping information between a windows laptop device and mobile devices in an offline (wilderness, no internet) environment. Would you know of available resources on this topic?



  1. Support Staff 1 Posted by Meghan on 20 Nov, 2021 01:52 AM

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    Hi Chris,

    You can use a JSON or GPX file to exchange map data between a laptop and mobile device while offline but it will have to be done manually. Unless you are going to get into some local server setup, there's no way that I know of to sync the data while offline to the same map.

    But we do have some pretty resourceful people who frequent the support forum- someone else might have a different suggestion.


  2. 2 Posted by caver456 on 20 Nov, 2021 02:41 AM

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    Hello Chris - I'm another user, not on the caltopo staff.

    Our SAR team does use a local server running Caltopo Desktop in our command
    trailer. Sometimes the server can talk to the internet thru a cell modem,
    sometimes not, depending on search location - but the local server keeps
    the local laptops in sync with each other regardless of
    internet connectivity, and the server itself syncs to the internet if and
    when it can, seamlessly, which doesn't take much bandwidth. That is pretty
    dang impressive, if you ask me.

    However, more to your question, a local server running Caltopo Desktop does
    not communicate with the phone app at all - it doesn't speak the same
    language, effectively - so like Meghan was pointing out, you need to do a
    hop-skip-and-jump to transfer a file between the laptops and the phone apps
    if there is no cell or internet.

    The app is pretty dang efficient at cell data usage though, and they
    continue to put tons of effort into that, so typically we'd just try to get
    some search assignments drawn early, before folks leave cell coverage
    enroute to the search. So they can get the assignment boundaries early,
    and then they can still record their own tracks (AppTracks) on the app
    without cell coverage, and export them from the phone app to a file on the
    phone when done. Then, transfer that file to the local server by whatever
    means - command trailer wifi, USB cable, etc. There's probably opportunity
    to streamline the whole phone-to-PC-data-transfer-without-cell-or-internet
    topic in general, though it's not specific to caltopo or any one app or
    program. However if the caltopo folks have some suggestions here, that
    would win.

    As a poor-substitute middle-ground, it should be possible to connect the
    phone to the command trailer wifi (we use a separate wifi for this, so that
    100 searchers connecting their phones to the wifi doesn't bog down the
    internal command trailer wifi used for keeping the laptops in sync with
    each other), then use a web browser to browse to the Caltopo Desktop
    server. You'd probably need to use IP address instead of server name, to
    avoid the need to do a name lookup which is problematic when offline. This
    same concept goes for anyone who needs to get to anything from the trailer
    server using their phone, when internet isn't available.

    I believe several SAR teams use a similar setup. Sorry if this is more
    info than you wanted!


  3. 3 Posted by cpt on 06 Dec, 2021 04:50 AM

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    When there is no cell connectivity, several of us have RavPower Filehub. This is a device that can sit between the Caltopo Offline Server and the mobile devices. From this you can upload/download.

  4. 4 Posted by John Pictin on 16 Dec, 2021 11:36 PM

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    In our setup, I run a local SARTopo Desktop installation loaded with tons of imagery and map data that we have put together. If the map was created by a manager online and they send the map URL (, I start my desktop instance and select the address and this pulls the map down from At this point, its usually a last known point, an ICP location and maybe an assignment or two. This makes the map accessible at that address by other workstations on the LAN. I also have them do a GEOJSON backup before they leave cell/wifi range so that in a worst case scenario I can simply import the map directly to my workstation. Our members use Avenza or the Caltopo app on their devices. With Avenza, the members import the map from the QR code on a printed copy. this puts a georeferenced PDF of their assignment on their device, and they can record a track as they go. If they have downloaded topographical maps in advance they have that as well. When they return from their assignment we copy the track off in GPX or KML and import it into our main map. If they are using the Caltopo app, and we have live connectivity, we can watch their track live - we give them a URL to login with update privileges. If we are offline, we can always import task assignments to their device or export the tracks afterwards and manually copy them to the map server. Sure it's not live, but we do get a good GPS track either way. We also use RadioLog which collects the GPS coordinates from our radios on each transmission and posts them to our SARTopo desktop instance. Our base radio could be connected directly to the SARTopo instance, but we utilize the log feature as an intermediary. Once the data is saved to our offline instance, it will sync to if and when we do get connectivity. I don't think I have missed anything but if you have further questions about our setup, please feel free to ask.

    Castlegar Search and Rescue

  5. 5 Posted by John Pictin on 16 Dec, 2021 11:47 PM

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    I forgot to mention, the import/export between SARTopo and the Caltopo app would be a matter of copying GPX, KML, or GEOJSON accross. When I export the file from SARTopo I would just select their assignment and any other pertinent points, like the ICP. There might be additional assignments that I may want to publish to them as well, so that they wouldn't have to necessarily come all the way back to the ICP to go right back to the next polygon. I hope that makes sense.

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