# GeomTOurs

user manuals and examples of the Android Apps of Urs Aebi

### Using old measurents or go and measure it again?

Following examples are calculated with BestNetwork.

Calculate new coordinates for a boundary in a forest. It is not possible to use GNSS. The approach is to traverse with a total station. The yellow points are unknown. For these points new coordinates have to be calculated.

I have the choice of using old measurements or measure a new traverse. What is the difference in accuracy. What do I gain with new measurement? Here the picture of the two equipments. For both choice I set an accuracy of 10 mm for known points.

Parameters:

- distance 2 mm + 2ppm

- direction 0.5mgon

- centring error 1mm

Parameters:

- distance 10 mm + 100ppm

- direction 1.5mgon

- centring error 10mm

**Task**Calculate new coordinates for a boundary in a forest. It is not possible to use GNSS. The approach is to traverse with a total station. The yellow points are unknown. For these points new coordinates have to be calculated.

I have the choice of using old measurements or measure a new traverse. What is the difference in accuracy. What do I gain with new measurement? Here the picture of the two equipments. For both choice I set an accuracy of 10 mm for known points.

**Traverse with new total station 2016**Parameters:

- distance 2 mm + 2ppm

- direction 0.5mgon

- centring error 1mm

**Traverse with DK-RT 1930**Parameters:

- distance 10 mm + 100ppm

- direction 1.5mgon

- centring error 10mm

**Result Traverse with new Total Station****- 8 mm****Result Traverse with DK-RT 1930****- 24 mm****24 mm is not bad. Consequently I us old measurements instead of going out into the forest and measure the traverse again. What would you do?**### Free Station (Resection) with 2 or 3 back sights

**2 or 3 back sights for**

**Free Station (resection)?**

Following examples are calculated with BestNetwork

**Free Station is also known as Resection. Get Location of the total station by measuring distance and angles to known points (back sights).**

**Free Station with 2 known points**

**(back sights)**:- 1 new point (station) with unknown coordinates are marked in red (point 3).

- Existing points with known coordinates are marked in green (points 1, 2).

- Station on point 3 with observations (orange lines) to point 2 and 3

**Free Station with 3 known points**

**(back sights)**:- 1 new point (station) with unknown coordinates are marked in red (point 3).

- Existing points with known coordinates are marked in green (points 1, 2 and 4).

- Station on point 3 with observations (orange lines) to point 2, 3 and 4

### Map and map navigation

**Navigation mode**Normally every click onto map generates points. This is very helpful to gather points immediately after the App started. Change to navigation mode when no points should be defined, for example when you want to pan (move the map). Deactivate Navigation mode with another click on the button.

**Zoom In!**

Click onto the plus of zoom control. Zoom control appears at the bottom of the map after a short click onto the map.

### Bad resection in a conventional survey

**The geometry of resections matters!**

You may have experienced this before. You are defining a new station and all points with known coordinates (back sights) are more or less in the same direction. Be careful in this situation.

**The situation explained with an example:**

Resection on point 1 with observations to known back sights on the road north of the site (green in following figure). Goal is to find the coordinates of point 5.

**Accuracy (blue error ellipse in map):**

Standard deviation is very bad 107 mm.

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