Redesign housing to support Slant Measurements

[tonycanike]

My Workbench

Facet 19029 (the one before the carrying case)

Feature Request

Redesign the Facet housing to support slant measurements of height above the mark. It's physically impossible to measure directly with a tape measure from a survey mark to the reference point of the GNSS housing (the bottom) when using standard survey tripods (heavy duty "legs", not a pole or bipod setup) due to the width of the head on standard survey tripods.

This is an issue with most commercial survey-grade GNSS receivers. Many commercial survey-grade GNSS receivers provide a secondary measurement mark for "slant measurements", where the tape is held at an angle from the survey mark on the ground to the edge of the diameter of the GNSS receiver. Many commercial survey data collectors allow the input of
a. the slant measurement - the length of the tape at an angle from the survey mark to the "slant" mark on the edge of the receiver.
b. the offset from the slant measurement to the phase center or bottom reference mark (I forget which at the moment.)
c. the diameter of the receiver at the slant measurement mark.
and the data collector uses a simple triangle formula to calculate the actual height of the antenna phase center above the survey mark on the ground.

Specifically, this includes

1. Increase diameter to allow a tape measure to run in a straight line from the mark to the case without touching survey tripod head or the tribrach. Standard survey tripods ("legs", not a pole & bipod setup) have a wide head and the current housing diameter is too small - one would have to bend the tape. Some manufacturers (eg. the Hemisphere 320/Carlson BRx5 have tabs (aka "ears") on the housing that increase the effective diameter and give clear place to measure from (or even hold the hook on the end of the tape). See Carlson's KB1042 (link below) for a diagram.
2. Put a slant mark on the housing (that the rubber bumper moves around needs to be resolved.)
3. Make the bottom of the Facet ROUND so that the slant height can be measured with a tape from any location and have a consistent radius. The current hexagonal bottom means there is no one radius.
4. Publish the radius of the housing at the slant mark
5. Publish the vertical offset from the slant mark to the ARP (the Antenna Reference Point, the center of the bottom of the housing; NOT the APC, as the APC moves with frequency and SV elevation and position.)
6. Create a diagram showing the radius and vertical offset from the slant mark to the ARP.

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OR it might be easier to just use a thin round disk of sheet metal with sufficient diameter between the Facet and the Tripod and slant measure to that. Hmmm. Similar to https://www.sparkfun.com/products/17519 (ground plane) but with a hole large enough for the 5/8x11 tripod screw.

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References

https://www.ngs.noaa.gov/AERO/Genspecs_A/Volume%20A_Attachment%2011-19.pdf
(Multiple docs in this PDF, Scroll down to "Attachment 13" page 3)

This document contains a great example of a diagram showing the radius and slant offset to the ARP.
https://web.carlsonsw.com/files/knowledgebase/kbase05.php?action=display_topic&topic_id=1042

https://kb.unavco.org/kb/article/introduction-to-gnss-antenna-set-up-methods-for-campaigns-71.html

[tonycanike]

Here's a great diagram:
https://www.e-education.psu.edu/geog862/node/1853