Let's do an Adjustment!
To give you a really quick start with GeoLab, we'll go through the steps of adjusting one of the sample networks installed with GeoLab. At this point you should have already downloaded (from our downloads page) and installed the GeoLab setup program (MGSetup.exe). Note that you can follow through the procedures below with GeoLab running in "demo" (unlicensed) mode.

Note that this article covers many of the points that were found to be common and helpful answers to questions from GeoLab users, and even experienced GeoLab users may find some useful tips here.

Run GeoLab by double-clicking the Microsearch GeoLab icon. With GeoLab open, let's first have a brief look at GeoLab's toolbar. One useful toolbar item is indicated in the screen shot at the left, which can be used to quickly open your IOB files. Click that button now, and select the Samples folder in your GeoLab installation folder. In that folder, double-click the file "simpletraverse.iob". This will open the IOB file we'll adjust.

What is an IOB File?
One of the main forms of input to GeoLab is a specially-formatted text file we call an "IOB" (an acronym for "Input OBservation") file. IOB files are simply text files that you can edit with any text editor, but editing them in GeoLab is much easier and more reliable. Each record (line of text) in an IOB file must be in a specific format, with all fields of data in the record in its proper location (within a pre-defined range of character positions (or columns) in the record. This may sound restrictive and error prone until you have seen and used GeoLab's "Record Editor". Before we have a look at the Record Editor, let's look at the rest of GeoLab's toolbar.

There are quite a few icons on the GeoLab toolbar, but we'll point out only two more of them that we find most useful. The screen shot at the right indicates these two icons, the first of which is used to bring up the Record Editor. The other icon, which we'll make use of very soon, is the second one indicated, and it is used to run an adjustment on the currently open IOB file.

So, let's use the Record Editor to have a look at the second line (or record) in the IOB file you now have open. Just left-click the mouse on the line beginning with " PADJ ...", and then press the F7 function key. This will display the Record Editor, and it should contain the fields of data for the PADJ record you clicked on. You should experiment with the Record Editor to learn all of its features. Mainly, the Record Editor allows you to edit and insert IOB records in the currently open IOB file. For now, just click the Close button to get back to your open IOB file.

We'll discuss a recommended layout for IOB files a little later, but first let's have a closer look at the IOB file you have open. This file contains 30 lines of text, but the blank lines, and the lines not beginning with a space or a '#' character are treated by GeoLab as comments. The lines beginning with an asterisk (*) character are comment lines as well (because they don't start with a space or a '#' character). The first four lines in this IOB files are "option" records, which we can ignore for now.

Commenting-out lines is easy when you have an IOB file open in GeoLab. To see how this works, left-click the " PADJ ..." line again, and press the F4 function key. Note that an asterisk character is placed in the first column of the line. Press the F4 function key again to un-comment the line.

Fixing Station Coordinates
Before we adjust this IOB file, let's examine a few record types. Look for the first line beginning with " NE ...". This is a "Northing and Easting" record. Click on that line and press the F7 key.

In the Record Editor you'll see all the fields for the NE record below the "Record Type" drop-down list (see the screen shot at the right). The first field is the "Fixed Coords" field which specifies which coordinates of the station are to be held fixed in the adjustment. If this field is blank or "000", none of the three coordinates (latitude, longitude, and height) will be fixed. The first of the three characters specifies whether the station's latitude will be fixed or free, the second character specifies whether the longitude will be fixed or free, and the third character specifies whether the height will be fixed or free. Note that any character other than a '0' (zero) or a ' ' (space) character will result in the corresponding coordinate being fixed. As you can see, we have fixed all three coordinates of this control station.

Click the Close button in the Record Editor to close it. You can see now that the first two NE records in the IOB file specify two control stations with all three coordinates of each fixed. The next two NE records specify the initial coordinates of the two stations "Point 1" and Point 2", and these two stations have no fixed coordinates. The adjustment of this traverse will therefore determine the best coordinates of these two stations with the given measurements.

Which brings us to the measurements in this IOB file. Near the end of the IOB file, you can see that there are three "DIST" records, and three "AZIM" records. The DIST records specify slope distance measurements, and the AZIM records specify (astronomic) azimuth measurements. When you look at these records in the Record Editor, you can see the values in their various fields. One of these fields, the "Sigma-ID" field, needs some explanation.

Using Sigma Records
Sigma records begin with the text " SIGM ..." and specify information about a measurement's accuracy that can be re-used in any number of measurement records. For example, to specify the standard deviation and centering errors for a group of distance measurements, we first create a SIGM record with appropriate values for the various fields. Then, when a distance measurement is entered, all we have to do is specify, in the DIST record, the Sigma-ID of the sigma record to use for calculating the standard deviation of that distance measurement. With this approach we can even leave the standard deviation field of the DIST record blank, because the SIGM record specifies all the information required for calculating the measurement's standard deviation.

Left-click on the second SIGM record ("SIGM dis...") and press the F7 key to view the fields of that record in the Record Editor. You can see that the distance standard deviation is specified as 0.010 m, with a PPM value of 2.0. Also, instrument and target centering errors are all set to 0.002 m. GeoLab will use all this information to calculate the standard deviation of any measurement that uses the Sigma-ID "dis".

Note that there is an "Aux Par Name" field in the SIGM record. This field is used to add an "auxiliary parameter" to a group of measurements. For example, if we create an "AUX" record to define an auxiliary parameter group with a "SCA2" (2D scale) parameter, we can assign that parameter to a group of distances by specifying the parameter group name in the "Aux Par Name" field of the SIGM record, and then use that Sigma-ID in all the distances in the group.

Using Options Records
Near the top of the IOB file you have open, left-click the "PADJ ..." record again, and press the F7 key. The PADJ record is an "options" record that specifies the coordinate systems you want your adjusted coordinates listed in. In the Record Editor you can see that we have chosen to list adjusted coordinates as "NEO" (northing, easting, and orthometric elevation) records, and that we want any adjusted auxiliary parameters ("AUX") listed as well (although we don't have any auxiliary parameters in this particular adjustment). For more information you can always press the F1 key.

Using Project Options
We should have a look at one more important GeoLab tool before we do the adjustment of this IOB file. In the Tools menu, click the "Edit Default Options" menu command. The dialog that comes up has five tabs along the top, and each tab contains a number of options that you can use to configure GeoLab. Click the "Adjustment" tab, and near the bottom-left of the dialog you'll see a drop-down list labeled "Default Linear Unit". Ensure that this is set to "m" for this adjustment. Before closing this dialog, you should explore it a bit to get familiar with the options available to you. To see more information about the items in this dialog, you can press the F1 function key.

Let's do the Adjustment
Close the "Edit Default Options" dialog to get back to your open IOB file.

Now click the toolbar icon specified above (in the second screen shot) as the one to "Perform an adjustment using the current text file". This toolbar icon is also shown at the left.

The Adjustment Results Summary Dialog
When you click that toolbar icon, GeoLab starts processing your IOB file, and then displays the "Network Processing Completed" dialog box. Click the OK button in this dialog to close it, and the "Adjustment Results Summary" dialog should appear. This dialog is very useful because it displays certain adjustment results related to the quality of your measurements, and the accuracy of your network station coordinates and coordinate differences.

For example, in the bottom left portion of this dialog, any standardized residuals greater than a specified value (see below) are listed. The second item in this list displays the value 1.200, and if you double-click this value, the cursor will be moved in the open listing file to a location near where that standardized residual is listed. If you close the Adjustment Results Summary dialog, you should see that the standardized residual of 1.200 is for the azimuth (AZIM) measurement from "Point 1" to "Point 2".

Note that you can open the Adjustment Results Summary dialog for an adjusted network by using the File/Open Adjustment Summary File menu command.

A Word About GeoLab Preferences
The GeoLab Preferences dialog can be opened by clicking the Tools/Preferences... menu command. This dialog has four tabs across the top. Click the General tab, and a group of controls labeled "Adjustment Summary Dialog Parameters". These are the settings that determine what is listed in the Adjustment Summary dialog when you do an adjustment. Press the F1 function key to see more information about this dialog.

The Adjustment Listing File
When you do an adjustment in GeoLab, the results of the adjustment are written to the adjustment listing file which is opened in GeoLab for you after the adjustment is complete. This listing file has the same name as the network's main IOB file, but with the extension "LST". The main sections of the listing file are as follows:

An easy method to quickly find a section in the listing file is as follows. Press the <Ctrl> key and hold it, and press the <Home> key to move the cursor to the top of the listing file. Then right-click the listing file and select "Go to Output Section", then click the name of the section you want to go to.

Using the VSCA record
As you can see, performing an adjustment with GeoLab is relatively easy. However, we have not discussed the full procedure for performing an adjustment. For example, in the adjustment we performed above, the variance factor was telling us that the variances of our measurements should be scaled by a value of 0.3107 (the estimated variance factor). So, let's do this now.

In the same IOB file that you still have open, click the 5th line (a blank line) and press the F7 key. The Record Editor comes up, and this time you want to select a record type in the "Record Type" drop-down list. Select the VSCA record type, and you'll see that this record type has only one field, the "Obs Vars Factor" (observation variances scale). Enter the value 0.31 in this field, and click the "and Close" button to the right of the Insert button.

You should now see a new VSCA record in your IOB file. This record tells GeoLab that the variances of all measurements that follow this VSCA record (and before the next VSCA record) are to be scaled by the value 0.31. When another VSCA record is encountered, the factor is changed to the value on that record, so you can scale the variances of different sets of measurements by different scales. When you want to reset the scale to 1.0 (no scaling), just use a VSCA record with a 1.0 in its field.

With this VSCA record inserted, you can now readjust the network, so click the toolbar icon for adjusting the current IOB file again. The adjustment will be done, and the Adjustment Summary dialog now tells us that the variance factor is 1.002177, and that the chi-square test on the variance factor passed. At this point we have completed the adjustment of the traverse.

Using Geoids in GeoLab
We did not use a geoid in the sample adjustment above, but normally the quality of your network adjustment will improve when you use a geoid model. There are two methods for using geoids in GeoLab. The most popular and easiest method is to use one of the geoids available for download from our web site and add that geoid to your network using a GFIL record. The second method is to use GEOI records in your IOB file. For more information on the GEOI record, please see the GeoLab help files.

A GFIL record has the following form:

This records instructs GeoLab to use the specified GSP file for information about the format and coverage of a geoid file. A GSP file is simply a file that contains information about the location, format, and coverage of a geoid file.

Note that both the geoid file and the corresponding GSP file must be downloaded from the above web page. Also, after you download these two files, you should place them in the same folder on your hard drive, and then use the Geoid Manager to ensure that the path to the geoid data file is set properly. To do this, open the Geoid Manager in GeoLab by clicking the Tools/Geoid Manager menu command. Click the Open button and browse to the folder where you saved your geoid file and the corresponding GSP file. When you are returned to the Geoid Manager, click the Browse button to the right of the Geoid data file edit box (see the screen shot at the right). Select the geoid data file and click OK. Finally click the Save button and close the Geoid Manager. You are now ready to use the geoid in your adjustments.

When you use a GFIL record, GeoLab will interpolate geoid undulation values from the specified geoid file for any stations that don't already have undulations defined. Remember to place the GFIL record after any initial coordinates you have in your IOB file so that the geoid interpolation will be done using the correct coordinates of the stations.

For the most accurate results when using a GFIL record, you should do the following:

• Place the GFIL record after any initial coordinate records in your IOB file;
• After you have cleaned up any problems with large observation residuals, copy the adjusted coordinates from your adjustment listing file into your IOB file, replacing the previous initial coordinates you were using.

This ensures that the initial coordinates used for geoid interpolation are the most accurate available, thus ensuring that the undulations used for all stations are the best available.

Recommended IOB File Layout
The last topic we'll look at briefly in this article will be a recommended layout for IOB files. This layout has proven useful to us in performing all sizes of network adjustments. Because it is common to have measurements of different types in a network, we will discuss the IOB file layout in terms of three such groups of measurements.

Let's consider the case where we have imported (using GeoLab's File/Import menu command) two sets of GPS measurements and one set of conventional traverse measurements as described in the following table:

The main IOB filename we will use is "MyNetwork.iob". The recommended layout for this file is as follows (note that any line beginning with a period (.) is a comment record):

Note that we have used the "#include" record type to insert our three different types of measurements in our main IOB file. This setup makes it easy to do the adjustment of each measurement group separately by simply commenting out the other two #include records. For example, if we wish to first do a minimal constraint adjustment using just the first group of measurements, all we have to do is comment out the #include records for the other two groups of measurements. Also, each group (file) of measurements begins with its own VSCA record, so it is easy to scale the measurements variances/covariance matrices of each group separately.