Notes on using an external GNSS receiver with smart phone mapping app

Transcription

1 Backgrund Within is a summary f my experience using varius GNSS (Glbal Navigatin Satellite System) receivers 1 ver the last 5 t 8 years. I like t recrd tracks summer and winter fr future use in returning t an area. I have stpped using Garmin hand-held GNSS units because f the cst and pr screen reslutin, and nly use smart phne mapping apps nw. I have decided t use an external GNSS receiver (Garmin GLO) instead f my smart phne internal GNSS, fr the reasns within. GLONASS is much mre effective in ur nrthern latitudes than GPS. GPS satellites, the riginal US system, circle arund the equatr, and require a clear view f the suthern sky. GLONASS is a Russian satellite system and the rbits are designed fr use in Russia, which suits Canadian mapping needs as well. There is als a Eurpean system called Galile that sme receivers als supprt. (iphne 8, Samsung Galaxy 8 etc.) Using bth GPS / GLONASS tgether is best in sketchy cnditins like heavy clud r precipitatin, r in canyns and muntains. In ther wrds, when yu really need it Sketchy GPS / GLONASS receptin may nt affect lat / lng accuracy that much, but it may lead t large errrs in altitude, which require several gd satellite fixes fr accuracy. GNSS receivers in recent phnes include GLONASS / GPS supprt: iphne 4S and newer, Samsung Galaxy S4 and newer, etc. The mst recent phnes als feature imprved GNSS accuracy, said t be cmparable t dedicated GNSS receivers. Battery life in yur phne is hammered by running yur "Lcatin" feature, particularly in lder phnes where the prcessr didn't pwer dwn the GLONASS receiver if it wasn't needed. external GNSS receivers are an ptin that save phne battery life and may ffer higher accuracy, especially if yu have an lder (r cheaper) phne. See Three tests f accuracy n page 5 fr my experience. My phne uses 40% r mre f its' battery - with its' internal "Lcatin" GNSS running - ver an 6-8 hr track, but nly 10% if an external GNSS receiver is used. 1 Cnfusing terminlgy! GNSS is used t refer t the GPS and/r GLONASS systems within, rather than using "GPS" as is cmmnly dne. Receiver is used t include all types f devices that receive GNSS signals, including hand-helds, smart phnes and external receivers Apr 15,

2 External GNSS receivers that are wrth cnsidering Make Mdel GLONASS? Battery Life (hr) Amazn.ca $ Battery Indicatr? Data Lgging Garmin GLO Yes 12 $120 srt f N Dual XGPS 150A N 8.5 $145 app n phne N Dual XGPS 160 Yes 10 $230 app Yes Bad Elf 2200 N 16 $195 Yes & app Yes Bad Elf 2300 Yes 24 $390 Yes & app Yes The tw receivers that dn't supprt GLONASS are nt wrth buying, IMO. Be careful if yu are buying n-line, in case yu accidentally buy ne f them! Battery life remaining is imprtant t knw. The GLO has a smewhat cryptic slid/flashing range LED that shws when it is in its' last hur r tw f life. The thers have LCD displays r n-phne apps that shw clearly what the battery life is. The GLO has a user-replaceable rechargeable battery, but extra nes can't be fund anywhere t buy - see belw fr what I did t fix this. The ther units are sealed, and must be recharged when the battery runs dwn. sme f the units have n-bard data lgging that allws them t recrd a stand-alne track withut using Bluetth t talk t the phne app. The track can be dwnladed t Gggle Earth back hme. This allws greater battery life, but is f limited use while navigating n a trip. What I have dne GNSS receiver - the Garmin GLO is cheap, and very reliable, based n 3+ years f use. The battery in it gives hrs - a full day, r even tw - f use. Since the nly ptin with greater battery life is very expensive (Bad Elf 2300 $390), I have bught a 2nd GLO just fr the battery. Charging bth batteries befre yu head ut gives yu 2 t 4 days f battery life. Phne - I have bught the rugged CAT brand S41 phne because f it's huge battery and bright screen and it's water-prf and drp-prf cnstructin. Running a map app n it with the Garmin GLO instead f the internal "Lcatin" uses abut 10% f the battery life per 6-8 hrs f mapping. Map app - I am using Gaia GPS with great results. Wrks n bth iphne and Andrid. Yu can use different map sets n it and the "OpenCycleMap HD" and Apr 15,

3 "Gaia Tp (meters)" are excellent. These maps are free, and ther maps are available at a cst. Gaia maps can be dwnladed and stred n the phne. Yu need a slid and fast internet cnnectin, as the maps can be 200+ MB. Yu must d this befre ging t the field, s plan ahead and dwnlad maps fr the areas yu frequent in advance. Gaia als needs a bit f time t lad the stred map s it appears n the screen nce yu have a GNSS fix. If yu dn't allw the map t appear and then start tracking, the map lading is verridden by the track recrding, it seems. I get gd results as fllws: put yur phne int Flight mde and turn Bluetth n start Garmin GLO Bluetth cnnect the GLO t yur phne (within 3 minutes, r the GLO pwers ff) let the GLO get a satellite fix (5 t 60 secnds) start Gaia and let a map appear hit the lcatin icn n the Gaia screen t mve t the GLO psitin let Gaia shw the map fr the GLO psitin start tracking. The entire prcess takes a cuple f minutes. anther feature that has been useful: Suthern Alberta Trail Mapping prject is a crwd-surced verlay fr tp maps, carefully put tgether by peple in Calgary. It cntains GNSS tracks submitted fr skiing, climbing, hiking and scramble rutes in Alberta and BC, currently, ver 800 separate rutes - have a lk at fr the tally! It is updated peridically, and the dashed line rutes appear n the OpenCycleMap HD and, it appears, the Gaia Tp map sets. Battery pack - if the trip is taking mre than the dual GLO battery life, I have bught the Anker PwerCre II prtable charger fr $36. Weighs 180 g, and takes up 7 cu inches. This will recharge the Cat phne 1x and the GLO several times. Recharging the GLO takes 4 t 5 hrs with a 5V, 1A charger. The newer wall chargers that put ut 2A r mre will charge the battery in 3 hrs. This is smething t cnsider if yu plan t use a prtable battery pack t recharge, as newer mdels can prvide mre than 1 A f current. Tricks t make it all wrk n Andrid phnes, yu have t use a 2nd, free app called Bluetth GPS t replace the internal "Lcatin" GNSS signal. me if yu need details n hw t get this set up - it is a bit cnfusing, but wrks reliably nce set up. Apr 15,

4 n Apple phnes, yu turn n the external GNSS receiver, and then set up as fllws (nt verified): lcatin services needs t be ON, airplane mde n, Bluetth n, and then Gaia advises Gaia GPS can use external GPS devices, which can als prvide greater accuracy and frequency than the built-in GPS. We use the best signal - the ipad/iphne will switch back and frth between the internal and external GPS, based n whichever surce has the best signal." ptinally, carry r munt the external GNSS receiver s it is high and facing up t the sky if pssible. I have a Velcr strip that attaches it t the tp f my packs, inside the zip pcket. Orient the receiver s the antenna faces upwards - n the GLO, that is the flat side with the indicatr LEDs. I have als carried it in a pant pcket with gd results. As always, if yu have gd satellite receptin, yu can put it anywhere in winter, the GLO wrks fine, but the battery life declines. At 20 C the GLO battery lasts 13+ hrs. At -10 C the battery life drps t 10 hrs. put yur phne int Flight mde, but turn n Bluetth. In Flight mde, the cell isn't cnstantly searching fr a twer which burns up battery life. I've had sme battery drain because f Ggle apps running because f a inadvertent swipe when handling the phne. I try t disable mst f these fr the reasn they seem t have a life f their wn running Gaia n my lder Samsung Galaxy 4S was hit-and-miss, as the prcessr seemed t freeze ccasinally. The Cat S41 is mre pwerful and has had n issues. If yu are having prblems with the "Lcatin" wrking n yur phne, turn ff yur phne's battery ptimizatin r pwer saving mde. If yu have mved a distance, i.e. > 50 km, since the last time yu used yur GNSS receiver, r it has been days r weeks since yu used yur GNSS, lck time can be increased because the GNSS receiver needs t dwnlad a new almanac (bunch f data) that is sent by the satellite. It cntains current inf n where all the satellites are. Apr 15,

5 Three tests f accuracy: The table belw shws three tests f accuracy using three different GNSS receivers. All f these were run n my pati and with the receivers statinary, s a perfectly accurate track wuld be a single dt, track length f 0, and n elevatin change. The GPS nly track (red) was recrded using an ld Garmin handheld, that I quit using because many times I went int trees r muntains, the track wuld start jumping arund by 500 m r mre. The track is very pr, ver 2 km in length! The blue track is using the phne "Lcatin" GPS/GLONASS and is much better than GPS nly. Hwever the elevatin inf varies by 150 m. The white track is using the Garmin GLO, ver 10 hrs. This track errr was cnsiderably less, with a distance f nly 33 m and elevatin variatin f +22 and -11 m. Track Clur GNSS Receiver Satellites Test Duratin (hr) Red Blue White Garmin etrex Legend HCx CAT S41 phne (internal) Garmin GLO (external) This image shws the three tracks n Garmin BaseCamp. Track Length (m) Elevatin Change (m) GPS / -65 GPS/GLONASS / -90 GPS/GLONASS / -11 Apr 15,