projecting coordinates a distance and bearing for DISTANCE sampling project

[bz...@bristol.ac.uk]

Dear All

I have a lot of data collected duriing DISTANCE samping, we have a waypoint where the observation was made, and the distance and azimuth to a gazelle sighting. I was wondering if anyone knows a downloadable extention, or any other way, that batch projects coordinates a specified distance and azimuth, and thus provides you with the coordinate of the sighted animal. 

Thanks

Steve  

[GIS in Ecology]

Hi Steve,

 

For this type of thing, I usually use the GEOFUNC add-in for Excell, which can be downloaded from here: http://www.afsc.noaa.gov/nmml/software/excelgeo.php. This provides you with functions in Excel that can be used to calculate the actual position of your animals from the position, distance and bearing/azimuth. The functions are

 

=NewPosLat(Lat1, Lon1, Bearing, Distance) for latitude and =NewPosLon(Lat1, Lon1, Bearing, Distance) for longitude, where Lat1,Lon1 is the position of the observer when the animal was seen. 

 

The position of the observer need to be in decimal degrees (you can find a converter for decimal degrees here: http://www.gisinecology.com/_files/Useful%20Tools/Decimal%20Degree%20Converter%201000%20Records.xls), and the bearing is in degrees, while the distance measure has to be in nautical miles (as this was originally put together for working with marine survey data). The conversion between mautical miles and meters is: 1 nautical mile = 1852 meters.

 

If you want, after you have downloaded and installed the Geofunc add-in for Excel, you can download an Excel workbook which has all the appropriate formula etc loaded into it from here: http://www.gisinecology.com/_files/Useful%20Tools/Position%20Estimator%20Workbook.xls, and you can just copy and paste your data into the ESTIMATED DISTANCE tab. You can use this to estimate the positions of up to 1000 animals at a time.

 

However, remember that the bearing/azimuth which is being used in this calculation is TRUE NORTH and not MAGNETIC  NORTH. This means that if you have recorded your bearings/azimuths with a magentic compass in the field, you will need to apply a correction to convert it from MAGNETIC NORTH to TRUE NORTH before you can estimate the positions.

 

Of course, this is all assuming that your positions are recorded in latitude and longitude. If your coordinates are in a projected coordinate system (i.e. aer in eastings and northings rather than lat and long), then it is a realtively simple bit of triganometry based on Pythagoras Theorem, and you can use the following formulae in Excel:

 

• Column A: Compass Bearing in decimal degrees
• Column B: Distance from base point in metres

Column C: =COS(RADIANS( [Column A]))*[Column B]

Column D: =SIN(RADIANS([Column A]))*[Column B]

 

Where Column C would be the Easting and Column D would be the Northing. However, you would need to make sure that your bearings/azimuths is in GRID NORTH rather than MAGNETIC NORTH. You can find out information about these different types of North here: http://googlecompass.com/TypesofNorth.htm.

 

I hope this helps, and if you need any further information on this, or need anything clarified (or find anything mentioned doesn't work for you), just post back on this thread.

 

All the best,

 

Colin

[lilian]

Dear Colin,

The Geofunc excel add-in does not seem to be supported anymore by NOAA.
Any chance you can send me the add-in to use your formula to calculate positions given a start point, bearing and distance?
Or else, do you have a matlab script handy? Thanks and very best wishes,
Lilian


Sent from my Windows Phone

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From: GIS in Ecology
Sent: ‎06/‎02/‎2015 10:18
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Subject: [GIS In Ecology Forum] Re: projecting coordinates a distance and bearing for DISTANCE sampling project

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[GIS in Ecology]

Hi Lilian,

Yes, this is an issue that the Geofunc add-on for calculating new positions based on distances and bearings isn't supportd by NOAA any more. I'm looking around for alternative solutions, but if anyone has code for doing this in QGIS, Grass, R, Matlab or Python, I'd be very interested to hear about it.

All the best,

Colin

On Sunday, October 30, 2016 at 10:12:38 AM UTC, Lili_Basking shark ecology wrote:

Dear Colin,

The Geofunc excel add-in does not seem to be supported anymore by NOAA.
Any chance you can send me the add-in to use your formula to calculate positions given a start point, bearing and distance?
Or else, do you have a matlab script handy? Thanks and very best wishes,
Lilian


Sent from my Windows Phone

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From: GIS in Ecology
Sent: ‎06/‎02/‎2015 10:18

To: gis-in-ecology-forum@googlegroups.com

gis-in-ecology-forum@googlegroups.com.

 
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