[Qgis-user] Advance Digitising Tools- compass bearings

[Kirk Schmidt]

Hi Calvin:

An interesting question.  Another consideration is the coordinate system 
for your project.  If it is a projected system, then you should consider 
convergence which is the angle between true north and grid north.  In a 
common example, UTM zone meridians are the center of each zone which are 
given an arbitrary easting of 500,000m.  If you are converting from 
magnetic to true north close to the meridian, then true north will be 
very close to grid north.  If you are east of the meridian, perhaps 
close to the adjacent zone boundary,  then grid north and true north 
will vary noticeably.

We developed a script for calculating convergence in UTM as I am unaware 
of a plugin provides that level of functionality. Ultimately, it will 
depend on the coordinate system you are working in.  If you reach out to 
me privately, I can share the script with you.

Kirk Schmidt

kirk at nortekresources.com

On 5/17/2024 9:15 AM, Jeremy Jackson via QGIS-User wrote:
>
>
> On 2024-05-17 07:00, C Hamilton via QGIS-User wrote:
>> Phil,
>>
>> The Shape Tools plugin has an "Azimuth distance digitizer" and for 
>> what you are talking about an "Azimuth distance sequence digitizer". 
>> With the latter function you click on a starting location and then 
>> give a list of azimuth, distance sequences. I have used this for old 
>> surveys like this. There is also an declination offset just in case 
>> your surveys were using magnetic north and not true north. In that 
>> case you have to look up what the
> A related question, what about grid to ground conversions and 
> vice-versa, are there plugins which support this?  Surveys here in 
> Canada always specify a "combined scale factor", which is tedious to 
> apply manually to each vertex when digitizing.
>> declination offset was for your 1880s date.
>>
>> Regards,
>> Calvin
>>
>> On Thu, May 16, 2024 at 9:50 PM Philip Ryan via QGIS-User 
>> <qgis-user at lists.osgeo.org> wrote:
>>
>>     Hello,
>>     I am trying to digitise a series of old gold lease "portion
>>     plans" produced in the 1880s in Australia by a mining surveyor
>>     using a compass and chain. The data for each gold lease includes
>>     a table of  1) compass bearings in degrees and 2) distance
>>     measurements in links (0.2 m) for each vertex of the lease
>>     polygon (mostly a rectangle or trapezoid but sometimes more
>>     complex).
>>     The Advance Digitizing Tools would seem to be ideal for this data
>>     except for the angle measure (a) which I can't input as a compass
>>     bearing (0-360 deg). The current settings with 90 deg E as the
>>     zero makes conversion of compass bearings very tedious.
>>     Is it possible to change the angle variable (a) to a compass bearing?
>>     Regards,
>>     Phil Ryan
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-- 
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
26 Church Road
Sutherlands River, NS
B0K 1W0
Tel (902) 922.3607
Email:kirk at nortekresources.com
Web:www.nortekresources.com
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