Posted: Oct 23, 2016 3:49 am
My boys and I are starting to learn geology. But first, they need to know how to read topographic maps, and locate themselves on the map.
Now, any fool can switch on a GPS receiver and find their location within about 10 meters in a few seconds. That's just fine, until your batteries are dead, etc, etc. My GPS receiver is an older Garmin GPS 12XL, which still works just fine. It's Mr. Backup.
I have an old Brunton pocket transit I picked up when I was in a tactical comms unit in Korea in the 1980s. I replaced the glass on it, and used a piece of toothpick as the needle locking pin actuator. I have a plastic Brunton Classic orienteering compass for each of the boys.
The US Geological Survey has 7.5 minute, 1:24000 topographic maps for free download. With some careful printing, trimming, aligning, and pasting, you can put together one of these maps. I have a plastic map cover I also got in Korea to protect the paper map. If anyone knows where, I'd like to get a couple more of those map covers.
That's the bearings we shot from features we could see. They don't converge very well:
I suspect we misidentified the two landmarks I marked on that image with pink arrows on the map. By using other sources of information available to us, namely, relative positions to known features (roads, trail intersection), we were able to eliminate the two erroneous sightings.
That positioned us within a 100 meter square at UTM coordinates DF 13T 72305730. Mr. Backup confirmed our triangulated location within 50 meters. Not too bad.
Sent from my iPad using Tapatalk
Now, any fool can switch on a GPS receiver and find their location within about 10 meters in a few seconds. That's just fine, until your batteries are dead, etc, etc. My GPS receiver is an older Garmin GPS 12XL, which still works just fine. It's Mr. Backup.
I have an old Brunton pocket transit I picked up when I was in a tactical comms unit in Korea in the 1980s. I replaced the glass on it, and used a piece of toothpick as the needle locking pin actuator. I have a plastic Brunton Classic orienteering compass for each of the boys.
The US Geological Survey has 7.5 minute, 1:24000 topographic maps for free download. With some careful printing, trimming, aligning, and pasting, you can put together one of these maps. I have a plastic map cover I also got in Korea to protect the paper map. If anyone knows where, I'd like to get a couple more of those map covers.
That's the bearings we shot from features we could see. They don't converge very well:
I suspect we misidentified the two landmarks I marked on that image with pink arrows on the map. By using other sources of information available to us, namely, relative positions to known features (roads, trail intersection), we were able to eliminate the two erroneous sightings.
That positioned us within a 100 meter square at UTM coordinates DF 13T 72305730. Mr. Backup confirmed our triangulated location within 50 meters. Not too bad.
Sent from my iPad using Tapatalk