Do cadastral survey with a total station, apart from having millimeter precision, it can also be useful for other purposes, given that the elevation of each point is counted. Let's see in this case, how to generate contour lines, that we already saw it with AutoDesk Civil 3D, with Bentley Geopak y Manifold GIS, so for educational purposes, in this case we will do it with ArcGIS.
1 CAD data
For this exercise, I have the survey files in dgn, one for each day of work. Importing it is as simple as:
- Data interoperability
- Quick import
The dgn files are selected, and ready, in all. See how pretty they look themed, you can see the days the guys worked, when they tried and when They cheered.
More than interesting, you can notice where they took points, in this case almost only in the course changes of the apples, to take the fronts and backgrounds with tape measure. Practical to support the method of survey for the moment of non-coincidences with documentary measures or other surveys. You can also notice where they mounted the team to look back.
2 Enter points to the geodatabase
For a better management, I will enter the points to a geodatabase. To do this, we assume that this is already created with the ArcCatalog and defined a Feature class.
- Conversion tools
- To geodatabase
- Feature class to geodatabase
3. Create digital model
Several of these steps can be overlooked, but for the purposes of understanding the use of 3D Analyst, we will see them in this order.
- 3D Analyst tools
- Create terrain
With this we have only defined the name of the model, we will enter the points:
- Add feature class to terrain
- Build terrain
Now we are going to generate the TIN
- ArcTool box
- 3D Analyst tools
- TIN creation
- Create TIN
You can see that at the ends that there are not enough points the triangulation stays poor, but where the streets are, consistency remains.
I could also notice that because of their innocence, in this uprising the boys erred by not keeping the elevation in a change of the apparatus. Salvable error, by interpolation of nearby points but the observation can be had in time to make the corrective. Also, suggest that in the first two georeferencing points use the elevation coordinate provided by the GPS and enough distance to reduce the rotation error due to the GPS inaccuracy.
4. Generate contour lines
Always within 3D Analyst
- TIN Surface
- TIN Contour
Here we choose the newly created TIN, the target layer and interval between the contours (among others pirouettes Which saves me for space reasons).
The steps are more when compared to Manifold GIS, but the options are much more powerful.
5. Generate slope map.
- TIN surface
- TIN Slope
What is coming is to use this, which can be applied to the design of sewage systems, as this is not only a land survey, but a topographic survey with which you can work street profiles with just a couple of steps .