Conventional Level Data Management

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Detailed Description

This video describes how to use the SAC conversion spreadsheet to convert data from a conventional level in angles and distances (polar coordinates) to Cartesian coordinates (northings and eastings). 


Date Taken:

Length: 00:05:04

Location Taken: Sacramento, CA, US

Video Credits

Terry Kenney, Megan Poff, Office of Employee Development


Part 1

Hi, this is Jeff Kitchen, I’m the surface water specialist for the data section in California. I would like to talk about the SAC-conversion spreadsheet which can be used to convert data from an azimuth-stadia-survey typically obtained using a laser or optic engineer’s level into the cartesian coordinate format needed for input into the iRIC program.

The iRIC-SAC program is the preferred software platform for running the USGS Slope Area Computation 1-D model, or SAC. This program requires input data that are in a X,Y,Z format or to be more specific to our surveys an Easting, Northing, and Elevation. If you are using GNSS or a Total Station for the survey you can easily create an input file from the instrument in this format. However, if you are surveying with a laser or optic level your data will be in polar coordinates, which are measured using angles and distances, and will need to be converted.

Part 2

Let’s open the SAC-conversion spreadsheet and take a look. The first sheet, named ‘SurveyData’, is where you will input your field data. The second sheet is the plan view plot of our data. The third sheet, named ‘Output’, is where the macro creates the final output file. There should be no need to change or interact with anything on this page. The last sheet, named ‘Read Me’ contains some of the basic instructions I will be discussing in this video. It also contains my contact information if you have any questions or issues regarding this spreadsheet.

Part 3

Let’s take a closer look at the ‘SurveyData’ sheet. Data that are input into the yellow highlighted cells on the left are converted into the X, Y, Z format which can be seen in the gray cells on the right. Let’s start with Hub-1. Since this is the starting point of your survey the angle and distance will be zero. The elevations of the hubs are not used in the planview or the computations performed by the spreadsheet and therefore are not required. However, I recommend entering them for consistency between the field notes and input file. Enter a remark if you wish. If you have additional hubs enter those now. The program assumes that Hub-2 was surveyed from Hub-1, Hub-3 was surveyed from Hub-2 and so forth. When one enters the angle and distance of the shot on Hub-2 the program will calculate a coordinate for Hub-2 based on the coordinate for Hub-1. Proceed to enter the hubs in the order they were surveyed. You can enter up to seven hubs. The spreadsheet can be modified if more are needed.

Part 4

Once all the hubs are entered we can start entering the rest of our survey data. The ‘Note’ column is the name of the surveyed point. A specific naming convention must be followed as described in the SAC-Tutorial. Angles can be entered as decimal degrees or degrees and minutes. If entering decimal degrees in the ‘Degrees’ column simply leave the ‘Minutes’ column as zero. The ‘Remarks’ column is where we can enter the details related to the point such as ‘fair debris line’ for a HWM. Enter a number in the ‘Hub’ column corresponding to the hub from which that point was surveyed. For example, if all of the survey was done from a single setup you would simply enter a ‘1’ for each point.

Part 5

When all the points are entered click on the ‘PlanView’ sheet to see a plot of the X-Y coordinates. Due to the auto-scaling feature of the plot, this planview may not be to the same scale along both axes but it should still allow you to check for any obvious entry errors. If you see a point that plots in an unexpected position double check the entry and modify if needed.

Part 6

The points will most likely plot on both sides of the axis. To avoid negative values, we can add an offset to our coordinates to make them all positive. We add this on the ‘SurveyData’ sheet using the ‘Offset’ cell. The value entered is added to both the Easting and Northing coordinates. We can see in this example that adding an offset of 300 causes all the values to be positive.

Part 7

Once all of your points have been properly entered and adjusted you are ready to export the data. From the ‘SurveyData’ sheet simply enter a file name into the highlighted cell and click the blue ‘Export File’ button to create the output file.

Part 8

We now have a file that is properly formatted for input into the iRIC and SAC-GUI programs.

If you need help contact your field office chief, surface water specialist, or indirect measurement specialist.