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Grid Reference Display Example Program
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51 28.3641 N
000 04.1209 W |
TQ 34231 76631 |
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| For airborne and vehicular video surveys there can be advantages to displaying map grid coordinates derived from
GPS data rather than the GPS data itself. We have had enquiries about whether our GPS overlay units can convert
GPS data and display Ordnance Survey (OS) grid coordinates. The mathematics required for the transformation between
latitude, longitude and the OS grid are too complex to be carried out by the 8-bit micro used in our OSD products.
Therefore our units cannot, by themselves, display OS, or other, grid coordinates. There are three ways in which
the desired result could be achieved using our units. |
| The simplest option is to use one of our gps overlay units to record latitude and longitude over your survey video
recording. Then, when the video is played back, locate areas of interest by converting the displayed position with
a Windows PC program called Grid InQuest. This program is available free from Quest
Geo Solutions Ltd. This is the best option if you have something with potentially only a few points of interest.
How acceptable depends on how many coordinates you need to convert as you need to type each one individually into
the program or into a file before conversion. |
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The easiest way to overcome the OSD project board's lack of computational power is to have the GPS to OS grid conversion
handled by a small program running on a laptop PC. The gps2grid Windows PC program which is included in our EXAMCODE
package is a simple example of how to structure such a program. The program receives latitude and longitude (OSGB36
datum) from a GPS receiver via the laptop's serial port, converts it to OS grid position and then outputs this
data, with commands to format it for display, via the serial port to one of our serial video text overlay units.
This will then display the OS grid position on the video. This is probably the easiest solution for creating a
OS grid on screen display. The example program uses the C++ source code written by Chuck Gantz to perform the GPS
to OS grid transformation. This code and reference material for the transformation can be found here. Code to transform from WGS84 to UTM is also included, but has never been tested. Our
example program is written in C and is provided as source code and as a Windows console program. The program uses
the freeware MFC CSerialPort class written by PJ Naughter.
To use this code on another platform you would need to supply the equivalent serial interface. A custom Y cable
is required to connect the three units together. Wiring details are supplied with the example program. |
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A more complex option would be the replacement of the laptop with an small PC compatible single board computer
module. This module could then run a version of our GPS -> OS grid example program. Combining the PC module
with one of our OSD boards would then create a dedicated unit. |
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© The BlackBoxCameraTM Company Limited 2008
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