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| -rw-r--r-- | www/ppp-howto.adoc | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/www/ppp-howto.adoc b/www/ppp-howto.adoc index e85e72f6..5018e377 100644 --- a/www/ppp-howto.adoc +++ b/www/ppp-howto.adoc @@ -68,7 +68,7 @@ spot? All GNSS systems compute positions using ECEF (earth-centered, earth-fixed) coordinates. After an ECEF position is calculated, it is -converted into latitude, longitude using a datum. So many to +converted into latitude and longitude using a datum. So many to choose from. You've probably heard of WGS84, NAD83, and maybe ITRF. NAD83 is pinned to the North American tectonic plate. WGS84 is pinned @@ -96,7 +96,7 @@ Original ITRF and WGS84 differ by less than 1 meter, which is huge for the purposes here. ITRF2014 and WGS84(G1762) differ by a few centimeters. -It gets worse. two expensive GPS often differ in altitude by over 60 +It gets worse. Two expensive GPS often differ in altitude by over 60 feet. Altitude is calculated as height above Mean Sea Level (MSL). But the Earth is not a perfect sphere. It is more pear shaped. In addition gravitational anomalies affect 'sea level'. @@ -145,7 +145,7 @@ There are many possible adjustments to the above procedure. Maybe you want to collect just 10 minutes of data to verify that your tool-chain is working before doing a 24 hour run. Simple, just change -`gpsprof -n 86400` to `gpsprof -n 360` and then proceed as above. +`gpsprof -n 86400` to `gpsprof -n 600` and then proceed as above. Maybe your _gpsd_ host does not have Python installed. Just run _gpsprof_ remotely. On the host you will need to run _gpsd_ with the `-g` parameter so |