Learn the concepts
The ideas behind the calculators, in plain words: what each one means, how it is worked out, and where the rules of thumb go wrong.
Pilots
- Holding pattern entries explained
The three holding entries, how your heading at the fix picks one, and how to fly each, for right and left turns.
- How to calculate crosswind
Headwind and crosswind from the runway and the reported wind, the clock-face shortcut, gusts, and your airplane's demonstrated crosswind.
- How to read a METAR
The groups of a METAR in the order they come, what each one means, and how the ceiling and visibility set the flight category.
- How to read a TAF
The valid period and each change group of a terminal forecast, and how to turn one into a timeline of what to expect and when.
- How to read a winds aloft forecast
The coded FB winds aloft forecast group by group, the three rules that trip people up, and how to find the wind between two levels.
- The wind triangle explained
Heading, groundspeed, and wind correction angle from your course, airspeed, and the wind, worked exactly and by rule of thumb.
- True north vs. magnetic north
What separates true, magnetic, and grid north, how the World Magnetic Model gives the angle between them, and how to convert a course without getting the sign backward.
- What is density altitude?
The altitude the airplane feels, why hot and high days lengthen the takeoff roll, and how to work it out exactly.
- What is pressure altitude?
The altitude on a standard altimeter setting, why 29.92 matters, and how QNH, QFE, and QNE fit together.
- When is it night in aviation?
Position lights, logging night, passenger currency, and Part 107 twilight each start at a different time. Here is when, and why.
- When to start descending
Top of descent from cruise altitude and groundspeed, the rules of thumb and how far they drift, and the visual descent point on a non-precision approach.
- Zulu time (UTC) explained
What Zulu time is, why weather reports and flight plans use it, and how to convert local time to UTC and back without the daylight saving slip.
Drone operators
- How far can you see a drone? VLOS explained
What "visual line of sight" means under Part 107, and a published method for how far out a drone of a given size stays in sight.
- How to estimate drone flight time
From the numbers on the battery label to minutes in the air, with a landing reserve and a cold-weather allowance.
- Photo overlap and flight lines explained
Front and side overlap, trigger distance, line spacing, the image count, and overlap loss over hills.
- Sunrise, sunset, and twilight explained
How sunrise and the three twilights are defined, why published times disagree, and what they mean for flying a drone near dawn and dusk.
- What is ground sample distance (GSD)?
How much ground one pixel covers, how to work it out, the height for a target GSD, and why GSD is not accuracy.
- What is the Part 107 altitude limit?
The 400 ft rule, the structure exception, and how to turn "above ground" into a number your drone or map can use.
Surveyors
- Geoid vs. ellipsoid height explained
Two kinds of height, the geoid height that links them, and the tens of meters you lose by mixing them up.
- Grid vs ground distance explained
Why state plane distances differ from tape distances, and the one factor that converts between them.
- Horizontal curves explained
The parts of a circular curve, arc versus chord degree of curve, stationing, and deflection-angle layout.
- NAD83 vs. WGS 84 explained
Datums, realizations, and epochs, and why a meter separates two systems people treat as the same.
- State plane coordinates explained
The flat grids US surveyors work in, how to find the right zone, and the 2 ppm foot that moves coordinates by feet.
- Traverse closure and precision explained
Angular and linear misclosure, the precision ratio, and how the compass and transit rules spread the error.
- Vertical curves explained
Grades, the parabola that joins them, K value, the high or low point, and elevations along the curve.
Developers and GIS
- Haversine vs. geodesic distance explained
Great circles on a sphere, geodesics on the ellipsoid, and how many kilometers the shortcut costs.
- How to choose an H3 resolution
Cell sizes at each H3 resolution, how to pick one for your data, and what pentagons and the hierarchy do to your results.
- Map tiles, zoom levels, and quadkeys explained
How web map tiles are numbered, why TMS flips the y axis, what a quadkey is, and the ground size of a pixel at each zoom.
- MGRS and USNG coordinates explained
Grid zone, 100 km square, and digits, and why a shorter reference is a bigger square, not a rounder number.
- UTM coordinates explained
The 60 zones, the 500,000 m false easting, the 0.9996 scale factor, and how to read a UTM coordinate.
- What is a geohash? Precision and edge cases
How a geohash is built, how big a cell each length gives, why nearby points can have different prefixes, and when to reach for H3 or S2.
Step-by-step guides
A job from start to finish, each step opening its tool with the values already filled in.
- VFR preflight
From the latest METAR to pressure altitude, density altitude, and the crosswind on your runway.
- VFR cross-country
Distance and true course between two airports, the heading to fly into the wind, the magnetic heading, and the time en route.
- IFR approach brief
The weather, the holding speed, the entry, the wind-corrected hold, and the visual descent point.
- Drone mapping day
From the resolution the client wants to the height, overlap, blur check, image count, and the hours of good light.
- GNSS control to OPUS to state plane
An OPUS position in ITRF2020 to NAD83(2011), then state plane coordinates, the orthometric height, and the combined factor for ground distances.
- Boundary retracement from a deed
Read the calls out of a deed, plot them and check closure, then rotate the bearings to the basis you found in the field.
- Lidar bid
The size of the site, the flight lines and flight time, the batteries it takes, and the accuracy you can state.
- Developer: index to area
Choose an H3 resolution for the cell size you want, index a point, inspect its cell and neighbors, and fill an area.