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Trail GPS

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If you are uploading a trail onto the OTC site, it is important to enter accurate GPS information. There are a number of ways to determine accurate GPS co-ordinates for a trail. Click Ontario Trail Network for more information.

Various kinds of GPS software are easily available for purchase or for free for different kinds of communication devices across the net. New models of smartphones come installed with GPS software. To get software for your communication device that suits your trail needs, click here.

If you know the street address for the trail, you don’t need to purchase any software. Many websites on the internet help you convert street addresses into GPS co-ordinates. Some of them are GPS visualiser and Geocode.

Coordinate Format Conversion Information for Submission of Trailhead Locations to OTN

Datum

Defined from:  http://www.esri.com/news/arcuser/0499/utm.html

A datum is a set of parameters defining a coordinate system and a set of control points whose geometric relationships are known either through measurements or calculation (Dewhurst, 1990). All datums are based on a spheroid, which approximates the shape of the earth.

The current standard datum to be used for data submitted to the OTN is Nad83.  Coordinates for trailheads based on sources another datum (such as Nad27) should be indicated as such on delivery, so that the datum can be converted prior to loading into OTN.  Coordinate locations can appear off in excess of 250m if Nad27 data is misrepresented as Nad83.

Geographic Coordinate System

The X coordinate refers to the Longitude.  Longitude is measured in reference to the Prime Meridian, which runs from the North Pole to the South Pole, passing through Greenwich, UK.  X coordinates to the West of the Prime Meridian may be expresses with the suffix “W”, or expressed as negative numbers, depending on the coordinate format.

The Y coordinate refers to the Latitude.  Latitude is measured North or South in reference to the Equator.  Y coordinates in the Northern hemisphere are expressed with the suffix “N”, or with positive numbers, depending on the coordinate format being used.

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Approximate maximum X and Y coordinate extents for the Province of Ontario

Trailhead coordinates found to be outside of the maximum X and Y extents shown above should automatically be re-checked to determine if there has been a map reading error or a transcription error.

Geographic Coordinates can be written in a few different formats.  The following examples demonstrate the expression of the same coordinate location using each method:

Degrees Minutes Seconds (DMS)
75˚40’44.48”W, 45˚26’18.11”N

Degrees Decimal Minutes (DM.m)
-75˚40.7413333, 45˚26.3018333’

Decimal Degrees (D.d)
-75.6790222, 45.4383639

Ideally, Decimal degrees should be recorded to at least 7 decimal places to maintain the level of precision required for entry into the data warehouse.

For the purpose of consistency, one format should be chosen for all trailhead coordinate records in the dataset. Additionally, it is important that there is consistency in the use of special characters, spacing and decimal places.  If a record contains a single digit, insert a zero as a placeholder.  For instance, 18.1” becomes 18.10”, or 9’ should become 09’. This becomes critical for maintaining columns when converting between formats using a spreadsheet method as described below.

Converting between degree formats

Decimal Degrees from Degrees Minutes Seconds

1. Import the table of coordinates into MS Excel
2. Insert three columns each after the X coordinate field and the Y coordinate field
3. On the Excel  toolbar select Data → Text to Columns → Fixed width

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4. Insert breakpoints to separate Degrees from Minutes and Seconds.  Also add breakpoints to separate punctuation characters from these columns

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5. Select “Do not import column (skip)” for each punctuation column, then click “Finish”.

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6. Add appropriate column headers such as X Degrees, X Minutes, X Seconds.
7. The two blank columns inserted after the X or Y field should have been populated by the process described in steps 3-5.  The third blank column should now be populated by inserting the conversion formula.

Assuming that the X coordinate now spans the three columns from A2-C2 the formula for converting X into Decimal Degrees is: =(ABS(A2)+((B2/60)+(C2/3600)))*-1
Assuming that the Y coordinate spans the three columns from E2-G2, the formula for converting Y into Decimal Degrees is:
=ABS(E2)+((F2/60)+(G2/3600))

Note:  The difference in the formula between X and Y reflects that all X coordinates in Ontario must be negative, and all Y coordinates in Ontario must be positive.
Also:  Additional attributed fields such as Trail number, and Trail name, and possibly others will be imported into the Excel file.  The column identifiers in the formulas must be adjusted according to the actual location of the X and Y data in the imported Excel sheet.

Decimal Degrees from Degrees Decimal Minutes

  1. This process is basically the same as steps 1-6, as described above in the process to convert DMS to D.d, with the exception that only two additional columns are added behind the X and Y columns.
  2. The formula for calculating X is =(ABS(A2)+(B2/60))*-1 and the formula for calculating Y is =(ABS(D2)+(E2/60))

A spreadsheet is useful when converting the coordinates for a large numbers of records.  If only a few records need conversion, or if you wish to verify the accuracy of the conversion formula, individual coordinates can be entered into an online converter such as the one located at:  http://www.directionsmag.com/latlong.php

Universal Transverse Mercator (UTM)

Although Geographic coordinates are preferred, some trailheads locations may have been collected as UTM coordinates.
There are 60 UTM zones across the globe.  Each zone spans three degrees East and three degrees west from the central meridian of the zone, with the central meridian assigned a false easting of 500,000.  (see http://www.esri.com/news/arcuser/0499/utm.html)
Ontario spans four UTM zones, and coordinates within a given UTM zone will be similar to coordinates at the corresponding location in an adjacent UTM zone, therefore it is critical that the UTM zone be specified when trailhead location data is acquired in UTM, or the data may appear in the wrong part of the province (500 km off).

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If trailhead coordinates are only available in UTM, it is recommended that the data be provided as-is for loading into OTN, along with information about the UTM zone and datum.