﻿ Croydon CycleStreets » Help and documentation

# Photomap help

## How it works: Photo Map

If the location of photos are known they can be overlayed on a map at the correct position. This section describes a way of recording longitude, latitude, orientation, date and time information in the filename of a digital photo. It enables them to be located anywhere in the world to accuracy of one metre, and in time to one second.

An arc of one millionth of a degree equates to about 10cm at the Earth's surface.

How many decimal places of longitude and latitude are needed to narrow a photo down to 1 metre accuracy on the Earth's surface?

Earth bulges at the equator, and so it is there that one degreee of longitude or latitude covers the most distance on the ground. Earth's equatorial diameter is 12,756.3 km. Assuming everything is perfectly spherical this gives a circumference of 12756.3 x pi = 40075.098km. Therefore 1 metre subtends (/ 360 40075098.0) = 0.00000898 degrees. That figure then is the minimum accuracy needed to identify 1 metre. Rounding this down to 0.000001 degrees (six decimal places: a millionth of a degree) gives accuracy of about 10 cm at the Earth's surface.

So, Lattitude can go from -90.000000 to +90.000000 and Longitude from -180.000000 to 180.000000. URLs do not like the + symbol, so n, s, e, and w are used instead of plus and minus symbols.

### Universal Media Naming Convention

This feature was deprecated 27 Jul 2009 14:00:03.

```		Name:              lleooo.oooooonaa.aaaaaaulllpbbba_yyyymmdd_hhmmss.jpg
String index:      0 2          13        23   28   33       42

Regular Expresion: ll[ew]{1}[0-9]{3}\.[0-9]{6}[ns][0-9]{2}\.[0-9]{6}[ab]{1}[0-9]{3}[nmf]{1}[0-9]{3}[ndouz]{1}_[0-9]{8}_[0-9]{6}\.jpg
```
• ll means longitude latitude
• eooo.oooooo (e or w) longitude w180.000000 to e180.000000
• naa.aaaaaa (n or s) lattitude can go from s90.000000 to n90.000000
• blll = (a or b, above or below) elevation in metres, where a000 (or b000) = ground level
• p = proximity, (introduced 19:51 11/11/2005) it refers to the distance of the main subject of the image, i.e. the one in focus. It is a single letter, one of:
• n near, up to a few metres
• m middle distance, about 10 metres - the default
• f far, out to infinity
• bbb bearing from 000 to 359, but usually mulitiples of 045
• a = azimuth, (introduced 10:55 13/04/2005) single letter, one of:
• z zenith
• u looking up
• o means looking horizontally, most photos are like this
• d looking down
• n nadir looking vertically down.
• yyyymmdd_hhmmss = date and time

The photo names are referred to by the more prosaic /location/number/, where number is the number of the photo, e.g. http://www.cyclestreets.net/location/2202/.

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