updated: 26-Nov-2009

 Copan for Windows

Field Resections Processing

Contents

Use this module to process raw total station surveys — circle readings, slope distances, and instrument and signal heights — based on resection (or free station) setups. Data can come from data logger files or be manually input. Resections are calculated using the best-fit of angle and distance shots to up to 10 control points. Resulting setup points and side shot points may be saved. Multiple resection surveys can be processed in a single session.

Note that, intersections, traverses, and two-faced observations are not handled here. (For intersections, use the § COGO Calculations module. For ordinary traverses, use the § Field Data Processing module and for bearing traverses use the § Field Bearings Processing module.)

Also note that, while there are certain similarities between the Map Traverse and the Field Data modules, there are various operational differences (other than the type of map/survey data involved). If you are familiar with one and new to the other, please study the appropriate manual and dialog carefully.

1. To Process Resection Data

1. Calculation | Process Field Resections...
2. Optionally Load... a field data File. (See § Field Files.)
3. Edit data in the big edit box as required. NB: To move the text cursor: Use the arrow, Tab, or Enter keys, or the mouse pointer. To manually insert a tab, copy and paste an existing one.
4. To enter setups and observations data, use the mini edit boxes and the relevant Insert button. To enter project, instrument and scales data, use the supplementary dialog via the More data button.
5. Save the Field file for reuse.
6. Optionally change the precision of displayed/listed distances and coordinates via Settings....
7. Calculate (or OK) to process the field data, accepting the resections as appropriate.
8. To graphically view the shots: Close the Info Display window if it is open, and minimize or move aside — but do not close — the Field Resections window.
9. Optionally List the field Data, the Calcs, or the Points that have been computed.
10. Optionally choose whether to Renumber new points or replace existing points (see § Point Renumbering or Replacement) and Save the Points that have been computed.

click for larger view

2. Resection Data Entry

Setups and Observations Data Entry

• For each resection instrument Setup, insert only the following:
  • At #   the free station point number,
  • Ht. Instr.   the instrument height — if elevations are required.
  They stay in effect until a new Setup is inserted. After a Setup line, multiple control shots and multiple side-shots can appear.
• For each "shot" Observation, insert the following:
  • To #   the target point number,
  • Hor. Circle   the horizontal circle value,
  • Vert. Circle   the vertical circle value (or zenith angle),
  • Slope Dist.   the slope distance,
  • Ht. Signal   the signal (or pogo) height — if elevations are required,
  • Code   a point code, if needed,
  • Note   a point note, if needed.
• For a remote elevation measurement (REM), insert it as an Observation but without a Slope Distance (or possibly also without a Horizontal Circle). See Remote Elevation Measurement in § Field Files for details.
• For the last control shot of each resection, be sure to use the end resect button so that an "end= resect" line precedes the side-shots.

Project, Instrument and Scales Data Entry

• Insert any desired Project data, anywhere. Note however, that, along with Instr. ID, such data are ignored during calculations.
• Insert any Scales or Instrument constants, whenever they differ from their previous values. These are (along with their default values)
  • Projection SF (1.0) for map projection distortion — applies only to horizontal distances,
  • Units Factor (1.0) for height and distance unit conversion (e.g., feet to metres),
  • Dist. Factor (1.0) for slope distance multiplicative correction (e.g., due to extreme temperature),
  • Dist. Corr. (0.0) for slope distance additive correction (e.g., prism constant),
  • VC Corr. (0.0) for adding to vertical circle values,
  and they stay in effect until new ones are inserted. Be sure to use the proper correction! In most cases, the default values are appropriate. A units factor of 3.2808399 is needed if measurements are in metres and coordinates are in feet.

3. Field Files

4. Resections File Example

at= 19                                                    HI= 1.7
        to= 84   HC=  0.0000   VC= 89.0005   SD= 27.566
        to= 85   HC= 85.2920   VC= 88.3020   SD= 19.040   HS= 1.2
        to= 86   HC=139.0800   VC= 88.0105   SD= 24.950   HS= 1.2
        end= resect
        to= 91   HC=111.2155   VC= 91.5835   SD= 10.120   HS= 1.2
        to= 92   HC=123.4405   VC= 90.2705   SD= 15.950   HS= 1.2
at= 21
        to= 86   HC=  0.0000   VC= 84.5950   SD= 13.904
        to= 85   HC= 85.0720   VC= 86.4505   SD= 16.355
        to= 83   HC=137.1830   VC= 82.3930   SD= 19.641
        end= resect
        to= 95   HC=299.4800   VC= 91.0740   SD=  8.180
        to= 95   HC=302.5440   VC= 92.1310   SD= 11.833

5. Calculation Method

The 2D portion of a resection is calculated is as follows:

1. Treat each control point's horizontal circle reading as a temporary bearing and, with reduced distances, compute temporary local coordinates for each control point relative to the setup point.
2. Determine the best-fit rigid-body transformation, by least-squares, of the control points from their temporary to their actual coordinates and show the residuals.
3. Transform the setup point using the estimated parameters.

Assuming the appropriate elevations and heights are present, the 1D portion of a resection is calculated is as follows:

1. Compute temporary local rises for each control point relative to the setup point.
2. Determine the average rise and show the residuals.
3. Transform the setup point using the estimated rise.

6. Notes

• Classic (or Tienstra) resection observations, involving angles only, are not supported.
• If you need to manually insert a tab, such as when you wish to add a code or remark to an observation line, copy and paste an existing tab — there will always be one between two auto-inserted attribute=value pairs.
• Both negative and zero values for HI or HS are correctly interpreted.
• If a setup's HI value is missing (or null), no elevations are computed.
• If either a resection control point's elevation or its HS value are missing, Copan ommits it from the elevation portion of the resection estimation.
• If a side-shot's HS value is missing, its elevation will be null.

updated: 26-Nov-2009