Mt Whitney Zone Forums General Discussion Gmap4 = View topos/aerials *offline* and your geolocation

I have posted here before about Gmap4 which is an enhanced Google map viewer that I developed. Up until this summer I believed that Gmap4 would not work if your mobile browser was offline.

I was wrong.

If you follow a few simple instructions, many (but not all) of the Gmap4 features will work just fine on a smartphone, tablet or other mobile device when you are offline. Among other things, when you are offline you can:
* Look at high resolution topo maps (t4 Topo High)
* Look at Google aerials
* Look at other basemaps
* Look at GIS overlays
* Turn on the geolocation feature (Menu ==> My location) and see the map become centered where you are standing
* Move and watch the location symbol follow you and the map automatically move as needed
* Touch the location symbol and see your coordinates in the current coordinate format
* Change the coordinate format
* Turn on/off a UTM grid
* Turn on/off a USNG grid

Yes, you can do all of the above while the browser in your smartphone or tablet is offline. Now let's pop the hood and see how this works.

Any map you see with Gmap4 consists of a bunch of small image files called "tiles" that are stitched together to cover your screen. When you look at a map while you are online, a copy of each image file is saved in the browser's cache. If you keep the browser tab open that has the Gmap4 map, then you can then go offline and still pan the map over the area for which there are map tiles in the browser's cache. If you pan too far, the screen will be white.

To read plain English instructions that I guarantee you will understand (I don't know how to write computer babble-speak) please visit the Gmap4 Help page and download the pdf file "How To Use Gmap4 Offline".
Help page: http://www.mappingsupport.com/p/gmap4_help.html

From the Help page you can also find the FAQ, examples, a Quick Start guide (also on the Help page) and more.

Gmap4 default map: http://www.mappingsupport.com/p/gmap4.php

Joseph, the Gmap4 guy

Joseph:
First, I fixed the text so your post would display. Any "curly" quotes and other characters you can't create from a keyboard cause the text to vanish. It's a php software bug caused by our hosting site upgrading. I need to upgrade the forum software.

Next: WOW! Gmap4 has been my favorite mapping tool for years, and this should make it even more interesting. I'll have to try out the features.

Question: All iPhones don't carry real gps receivers, only the latest, if I understand correctly. So the phone's ability to locate its current location depends on being near cell towers, is that correct?

> To read plain English instructions that I guarantee you will understand (I don't know how to write computer babble-speak) please visit the Gmap4 Help page and download the pdf file "How To Use Gmap4 Offline".

That's hilarious! Microsoft is truly the best at creating computer "babble-speak", complete with their "did you find this helpful" question boxes at the end.

so the moment I power down my phone to save battery and start it back up, all the cached pages are gone

Going to hang on to my aging Garmin 60csx for a few more years.

@Steve C

1. Thanks for the fix

2. Here is something I read online:
"Yes, the iPhone 3G and 3GS have a GPS receiver built-in. The original iPhone does not."

Also, I know that starting with the iPhone 4s, there is a better GPS chip in the iPhone. It is better since it can also see the Russian satellites (GLONASS). More sats = more data = better accuracy. But!!!, your phone can only use the Russian data if your phone has a current almanac for the Russian sats. For details see the pdf file on the Gmap4 Help page.

Sad but true.
Also, if you power down and are not in cell range then you cannot start Gmap4. You can only start Gmap4 when your browser is online.

If you are on a day hike then one option might be to leave your phone on but your GPS off. (GPS is a battery hog) Only turn the GPS on when you need to check position.

Joseph,

Have you considered "partnering" with one of the Apps that are used for hiking/biking/etc? They often offer offline map storage within the app, but not with the functions your have with Gmap4. One app I use a lot is "ViewRanger". It offers a great deal of functionality, and would benefit from Gmap4 I believe. This might help you get around the limits of browser cache memory.

John

Alas, a mobile browser app lives in its own 'sandbox' and cannot access memory used by a browser native app.

Also, Google's terms of service bar anyone from writing their own code to cache Google's tiles.

Besides, if I wanted to cache more tiles than allowed by mobile safari I would simply also start up mobile chrome before going offline.