Category Archives: Maps

Check Out the New Elevation Profiles!

forester_elevation_profile

Halfmile’s Pacific Crest Trail maps have been updated for 2015 and they include cool new elevation profiles created by programmer Tom “66” Reid.

Colors used on FAA charts.

Colors used on FAA charts.

The new elevation profiles feature color coding in the style of FAA Aeronautical Charts, improved formatting to show more waypoints, and mileage that matches the 2015 Halfmile PCT mileage estimates.

Information on the elevation profiles includes:

  • Page numbers to identify which PCT map pages are covered.
  • Black dots for every half mile of trail.
  • Red dots marking individual waypoints along the PCT.
  • PCT mileage from the Mexican border every two miles.
  • Elevation gain/loss is estimated (see the red circle above) for every two mile section of PCT.

The new elevation profiles are included with each section of PCT maps, or just the new elevation profiles for California can be downloaded here, or Oregon/Washington profiles can be downloaded here. Since PCT mileage estimates have changed for 2015, be sure not to mix and match 2014 and 2015 version of PCT maps, apps, or GPS data.

Waypoint Abbreviations

Waypoints

Waypoints

We have been asked by several hikers about the abbreviations used for waypoint names on Halfmile Project PCT maps, apps, GPS data, and Google Earth files. Here is a list of the most common abbreviations:

BB — Bear box or bear locker (mostly in the Sierra)
CG — Campground
CS — Campsite
GT — Gate
JMT — John Muir Trail
Hwy — Highway crossing
NF — National Forest boundary
TH — Trailhead
TR — Trail
PL — Powerline
PO — Post Office
RD — Road crossings
RR — Railroad track
Ski — Ski lift
Wild — Wilderness boundary
WA — Possible water source (not on www.pctwater.com, mostly north of mile 700)
WR — Possible water source listed in the PCT Water Report at www.pctwater.com
WACS — Possible water source and campsite
WRCS — Possible water source from the Water Report and campsite

Curious which waypoint types are most commonly used? Here is a list from the new 2015 Halfmile Project data:

3161 — total number of 2015 waypoints
972 — WA waypoints
745 — CS waypoints
498 — TR waypoints
466 — RD waypoints
152 — WR waypoints
73 — GT waypoints
61 — Hwy waypoints
54 — PL waypoints
33 — Wild waypoints
21 — CG waypoints
16 — BB waypoints
12 — TH waypoints
8 — PO waypoints
6 — NF waypoints
6 — Ski waypoints

About the 2015 Halfmile Updates

Updating maps for 2015

Updating maps for 2015

The 2015 Pacific Crest Trail hiking season is rapidly approaching and understandably we have been getting questions about what’s changing in the 2015 edition of Halfmile’s PCT maps and when new maps, apps and GPS data will be ready.

2014 was a massive data collection effort for the Halfmile Project team. Halfmile and Dirt Stew thru-hiked the PCT (Halfmile northbound, Dirt Stew southbound) carrying very accurate custom GPS devices designed for mapping long hiking trails. 8,296,179 new data sample points and 5,065 new waypoints were collected.

GPS reception can be challenging along some parts of the PCT due to tree cover or terrain such as mountains or canyons that sometimes block GPS signals. This is especially true in Oregon and Washington. The custom GPS logging hardware performed amazingly well because of the outstanding performance of the ublox NEO-7P GPS module, external mast mounted antennas, and the merging of multiple GPS data sets using software developed by David Lippke. We are confidant this is the most accurate data ever collected of the PCT.

Overall the new 2015 data has an average horizontal accuracy of 1.9 meters. Here is the horizontal accuracy by PCT section:

CA Sec A: 0.67 meters
CA Sec B: 1.26 meters
CA Sec C: 1.11 meters
CA Sec D: 1.19 meters
CA Sec E: 0.81 meters
CA Sec F: 0.98 meters
CA Sec G: 1.18 meters
CA Sec H: 1.44 meters
CA Sec I: 1.62 meters
CA Sec J: 1.51 meters
CA Sec K: 1.61 meters
CA Sec L: 0.49 meters
CA Sec M: 0.57 meters
CA Sec N: 0.46 meters
CA Sec O: 0.68 meters
CA Sec P: 1.92 meters
CA Sec Q: 2.37 meters
CA Sec R: 2.19 meters
OR Sec B: 2.66 meters
OR Sec C: 2.49 meters
OR Sec D: 2.57 meters
OR Sec E: 2.32 meters
OR Sec F: 2.45 meters
OR Sec G: 3.78 meters
WA Sec H: 3.45 meters
WA Sec I: 2.94 meters
WA Sec J: 1.75 meters
WA Sec K: 3.34 meters
WA Sec L: 2.42 meters
Continue reading

Elevation Gain on the Pacific Crest Trail

elevation profiles

Halfmile’s PCT Map elevation profiles.

Pacific Crest Trail hikers are often interested in knowing the elevation gained or lost as they hike along the Pacific Crest Trail. The 2014 Halfmile Project estimates the total elevation gain/lost for a northbound thru-hiker is 489,418 feet of climbing and 488,411 feet descending with an overall change of 1,007 feet as they hike from Campo to Manning Park.

Here is a breakdown of elevation gain/loss by PCT section:

Gain Loss Change
CA_Sec_A 16,452 -16,335 117
CA_Sec_B 19,006 -20,698 -1,692
CA_Sec_C 22,427 -20,775 1,652
CA_Sec_D 26,944 -27,403 -459
CA_Sec_E 21,200 -19,894 1,306
CA_Sec_F 14,891 -13,469 1,422
CA_Sec_G 23,576 -18,061 5,515
CA_Sec_H 32,804 -34,987 -2,183
CA_Sec_I 14,320 -13,257 1,063
CA_Sec_J 14,049 -16,282 -2,233
CA_Sec_K 10,661 -10,887 -226
CA_Sec_L 5,282 -7,893 -2,612
CA_Sec_M 18,095 -20,421 -2,326
CA_Sec_N 17,106 -16,424 682
CA_Sec_O 17,961 -18,747 -785
CA_Sec_P 19,147 -15,326 3,821
CA_Sec_Q 9,311 -13,918 -4,608
CA_Sec_R 14,290 -11,390 2,900
OR_Sec_B 8,124 -7,427 697
OR_Sec_C 9,008 -8,056 951
OR_Sec_D 7,588 -8,422 -834
OR_Sec_E 9,614 -9,394 220
OR_Sec_F 15,476 -16,619 -1,144
OR_Sec_G 8,965 -12,924 -3,958
WA_Sec_H 29,552 -25,348 4,204
WA_Sec_I 18,327 -19,744 -1,417
WA_Sec_J 18,773 -17,711 1,062
WA_Sec_K 31,441 -30,641 799
WA_Sec_L 15,030 -15,958 -928
Total 489,418 488,411 1,007

It turns out that estimating elevation gain/loss is a surprisingly complex and technical process. The Halfmile Project has put a great deal of effort into this, and our estimates are much more accurate than, say, the ones that Google Earth produces, or any other source of PCT information.

Elevation values obtained from GPS units are much too noisy for use in gain/loss calculations — even from the survey grade equipment that we now are using on the Halfmile Project. Instead, elevation data is based on USGS 1/3 arc second DEM (Digital Elevation Model) data.

Halfmile Project gain/loss estimates use approximately 3/4 million GPS sample points along the Pacific Crest Trail. The elevation for each sample points is calculated based on a grid of 525 USGS 1/3 arc second DEM rectangles that surround the point. A two dimensional spline interpolation is then generated using the DEM rectangles to calculate the exact elevation of each sample point.

elevation spline plot

Blue lines are the elevation spline plots calculated based on 525 USGS DEM elevation rectangles. The center of each DEM rectangle is marked with a black dot. The elevation of a GPS sample point is then calculated, in this example as 1,252.04 meters. The process is repeated about 3/4 million times.

Observant (or obsessed) readers may have noticed that the Halfmile Project elevation estimates changed slightly from 2013 to 2014. This year’s total elevation gain of 489,418 feet is slightly less than the 492,871 foot estimate last year. The reason for the changes are:

  • The DEM data itself is constantly being updated and improved by the USGS.
  • In some sections of the PCT we completely replaced the data with more accurate GPS data.
  • In all sections we changed our selection of points (i.e., doing a bit smarter job this year).
  • Last year’s interpolation was from a grid of 36 surrounding points and this year 525 grid points were used.

While these changes are very small, even small changes add up over thousands of points.

One reason we put so much effort into elevation calculations, is so that the elevation gain/loss estimates match between the printed maps and smart phone apps. The Halfmile smartphone apps calculate very accurate elevation gain/loss estimates between your current on-trail location and any landmark along the trail.

Here the Halfmile smartphone app estimates an elevation gain of 7,102 feet and a loss of 4,047 feet from the Southern Terminus to the water fountain on Mt Laguna near Burn Rancheria Campground.

The Halfmile smartphone app estimates an elevation gain of 7,102 feet and a loss of 4,047 feet along the Pacific Crest Trail from the Southern Terminus to the water fountain near the Burn Rancheria Campground.

If you want even more details about Halfmile Project elevation estimates, David Lippke AKA White Jeep posted a detailed summary recently on the PCT-L. Here is a copy of what he posted:

Hi, Lon alerted me regarding the PCT elevation gain/loss stats conversation here and so I thought some direct information might help. I’m the author and maintainer of the Halfmile apps and I generated all the elevation data and gain/loss numbers published for the last three annual cycles. I spend most of my time working on improving both the horizontal and vertical accuracy of all our PCT data. This effort has ballooned over the last couple years involving more than just myself and Halfmile with the deployment of survey grade equipment to the trail, custom GPS logging devices, and now further generations of all that we are scrambling to deploy for the 2014 season.

Anyway, people often wonder how we calculate elevation gain and loss numbers along the PCT. It turns out that this is a surprisingly complex and technical process. The net is that we currently generate profiles that are much more accurate than, say, the ones that Google Earth produces. That said, there is still substantial room for improvement and we are working on that.

The technical TLDR is that our point elevation values are produced by heavily processing USGS DEM 1/3 arc second data. Our gain / loss calculations then operate over this set using a smoothing factor consistent with the average error present in the DEM data and the average horizontal “side to side” path jitter observed along side slopes.

Most will want to stop reading here. 100% tech talk follows. You have been warned. 🙂

Going on in more detail, the process does not involve using GPS elevation data at all. As noted by Brick, elevation values obtained from GPS units are much too noisy for use in gain and loss calculations — even from the survey grade equipment that we now use. Instead, our raw source for elevation data is the USGS 1/3 arc second DEM (Digital Elevation Model) which provides average elevation values over rectangles that are approximately 8×10 meters on a side (the “8” varies with latitude).

We start with our best filtered GPS horizontal data for each bit of trail. This ranges in horizontal accuracy from 1/2 meter (California sections L through O) to 3-5 meter accuracy (e.g., WA J) to unknown accuracy data that we hand select from the competing data sets. Over 2014 for the 2015 update, we hope to bring the average horizontal accuracy for the entire PCT to the vicinity of a single meter.

Then we translate all those horizontal points to the horizontal datum used by the USGS and we fetch the DEM elevation values needed generate a grid of 525 points surrounding each subject point. Using those 525 points, we generate a two dimensional spline interpolation and query it at the exact point. This process is repeated for all 3/4 million horizontal data points and involves almost 11 million unique 1/3 arc second DEM values.

So at this point in the process we have the best possible estimate for the elevation of each track point and way point expressed in terms of the NAVD88 vertical datum (quasi MSL) with the primary error sources being that of the USGS DEM (RMSE ~2.5 meters) and that of our collected horizontal positions.

In the next step, we reduce the horizontal point count so that all sections stay within Garmin’s 10K track point limit. We do this by applying the Ramer-Douglas-Peucker algorithm with a 1.9 meter sigma overall and, in more accurate sections, a 1.25 meter sigma. In other words, when the trail is going along a straight road or the aquaduct, the points can be several hundred meters apart but in tight turns they may only be a couple meters apart.

Finally, to calculate gains and losses between points, a tally is kept from track point to track point except that no gain or loss is recorded until a track point is reached that has an elevation loss or gain more than 5 meters from the starting track point. When that occurs, the algorithm moves forward to the current end track point and picks up the counting again. When reporting the gain / loss to a particular way point, any residual in the smoothing is closed out so that the numbers all “add up”. As a side note, this creates a small numerical issue when one decides to total our published per-section numbers over the whole trail and compare those to the whole trail numbers in the (soon to be released) 2014 version of the Halfmile apps — our per-section numbers are “closed out” with respect to this 5 meter smoothing but the app just keeps rolling through the boundaries.

Sorry for the tech talk, but I just wanted to address all the speculation about what feeds into these calculations. Questions are always welcome and so is project involvement — we have all manner of “task” available for the inclined. 🙂

All the best,
David Lippke aka White Jeep

2014 update change list

Wondering what changed in the 2014 version of Halfmile’s Pacific Crest Trail Maps and GPS data? Here is a list:

Changes to all sections:
Gain/loss estimates on elevation profile pages recalculated for improved accuracy and consistency with smartphone apps
Acrobat bookmarks added to .PDF files
Mobile optimized .PDF files created (smaller size due to increased compression)

CA Section A
RD0064 – corrected typo
WR091 – updated location

CA Section B
No Changes

CA Section C
Updated track near mile 220.5
Moved half mile point 220.5
Renamed WR226 to WRCS226
Added WRCS229
Added WRCS231
Added WRCS232
Added WR233
Removed WR234
Renamed WR235 to WRCS235
Renamed WR239 to WRCS239
Renamed WR240 TO WRCS240
Renamed WR256 to WRCS256
Added RD0258
Added WR258
Added RD0258B
Added WRCS258
Added Cougar Crest Trail
Removed BigBearHostel waypoint from GPS data (it’s not on any map)
Removed BigBearLakePO waypoint from GPS data (it’s not on any map)
Removed Nature’s Inn

CA Section D
Renamed MessengerFlat to MessengerFlats
Removed ActonMetrolink from GPS data (it’s not on any map)

CA Section E
Updated description, location for the spring at WRCS494

CA Section F
Added BV0570
Added BV0571
Added CS0571B
Added CS0573
Added CS0574
Added RD0575
Added RD0579
Updated description WR583
Added PL0584
Added GT0590
Added RD0600
Added RD0601
Added TR0602
Renamed WR602 to WRCS602
Added RD0605
Renamed WR609 to WRCS609
Added RD0609
Added RD0618
Added Gully0620
Added DoveSpringCynRd
Added WR620
Added RD0622
Added RD0624
Added RD0625
Added RD0628
Added RD0630
Updated description of WR631
Added CS0634
Added CS0635
Added TR0637
Renamed WR638 to WR637
Added RD0641
Added RD0644
Added McIivers Spring track to map and GPS data
Added Willow Spring track to map and GPS data
Added Robin Bird Spring track to map and GPS data
Added Willow Spring Alternate track to map and GPS data
Removed PO0652 from GPS data (it’s not on any map)
Renamed water warnings from mile 620 – 664
Updated Lake Isabella PO hours
Updated Onyx PO hours

CA Section G
Added bear canister information on map pages 6 and 14

CA Section H
Updated Red’s Meadow description

CA Section I
No changes

CA Section J
Corrected small error in track near the Sonora Pass picnic area

CA Section K
Renamed WA1194 to WACS1194

CA Section L
Survey grade GPS data collected for this section (sub-meter accuracy)
Improved mileage estimates based on more accurate GPS data
New half mile waypoints created based on more accurate GPS data
Added track to rest area
Renamed WA1182 to WA1181, moved to switchback 1/10 mi south
Renamed WA1194 to WACS1194
Removed Red Moose Inn

CA Section M
Survey grade GPS data collected for this section (sub-meter accuracy)
Improved mileage estimates based on more accurate GPS data
New half mile waypoints created based on more accurate GPS data
Renamed RD1204 to RD1205
Renamed WA1205 to WACS1205
Renamed CS1211 to CS1212
Renamed WA1211 to WA1212
Removed CS1216
Added WACS1216
Removed WA1216 (at cow pond)
Added trail to WA1216 track
Added new WA1216 at piped spring
Renamed WA1219 to WA1220
Renamed WA1224 to WACS1224
Renamed WA1231 to WA1232
Renamed CS1232 to CS1233
Removed PO1236 from GPS data (it’s not on any map)
Renamed RD1241 to RD1242
Renamed RD1244 to RD1245
Removed CS1251
Renamed WA1251 to WACS1251
Renamed RD1263 to RD1264
Renamed WA1267 to WA1268
Renamed WA1277 to WA1278
Moved WA1278 to more accurate location, renamed WA1278B
Renamed CS1278 to CS1279
Removed CS1280
Renamed WA1280 to WACS1280
Moved WA1284 to better water source

CA Section N
Survey grade GPS data collected for this section (sub-meter accuracy)
Improved mileage estimates based on more accurate GPS data
New half mile waypoints created based on more accurate GPS data
Renamed CS1295 to WACS1295C
Renamed CS1302 to CS1301B
Renamed WACS1303 to WACS1302
Renamed WACS1309 to WACS1308
Renamed RD1309 to RD1308
Renamed WA1332 to WA1331
Renamed WA1339 to WACS1338
Renamed WA1345 to WA1344
HatCreekView added
CS1384 added
StandByMeBridge added

CA Section O
Survey grade GPS data collected for this section (sub-meter accuracy)
Improved mileage estimates based on more accurate GPS data
New half mile waypoints created based on more accurate GPS data
Renamed RD1425 to RD1424B
Renamed RD1453 to RD1452
Renamed WA1468 to WA1467
Renamed WA1469 to WA1468
Removed waypoints from GPS data that were not on any map

CA Section P
No changes

CA Section Q
No changes

CA Section R
Removed waypoints from GPS data that were not on any map

OR Section B
Updated Fish Lake Resort zip code

OR Section C
Updated Mazama Village shipping address

OR Section D
Updated Shelter Cove Resort phone number

OR Section E
Added information about camping restrictions in the Obsidian Limited Entry Area
Updated Elk Lake Resort shipping information

OR Section F
No changes

OR Section G
Updated Timberline Lodge shipping address, phone

WA Section H
No Changes

WA Section I
No Changes

WA Section J
New GPS data collected for this section (five new tracks merged for greatly improved accuracy)
Improved mileage estimates based on more accurate GPS data
New half mile waypoints created based on more accurate GPS data
Added note that the Chevron Station may not accept packages
Renamed WACS2445 to WACS2446
Renamed WA2455 to WA2456
Corrected description of Goldmyer Alternate (mile 11.4), where you do not cross the bridge but continue on E side of river

WA Section K
No Changes

WA Section L
No Changes

Halfmile’s updated 2014 maps are online

Halfmile’s Pacific Crest Trail maps have been updated for the 2014 hiking season and are now online as free .PDF downloads. The updated maps include suggestions from 2013 hikers, more than 400 miles of new GPS data collected with survey grade GPS equipment in California Sections L – M, and new smaller files optimized for mobile devices (in addition to standard files optimized for 8 1/2 x 11 printing).