Correct GPS elevation readings for geoid heights with GeoMedia

Intergraph GeoMedia's coordinate system engine can be used to convert your GPS receiver's elevation readings to the correct topographic height taking into account the reference geoid height. Besides GeoMedia, I have not seen vertical datum conversion functions in other software like Global Mapper or Safe FMe but I am sure ESRI ArcGis should have those functions too. For more information about geoid correction for GPS and topographic height, you can visit this site.

As an example of using GeoMedia to convert the GPS measured elevations to topographic height, I use an Excel spreadsheet containing just 2 GPS points as shown below as my source data.

And now, the procedure. There are many ways to read in data in GeoMedia but in this example I chose to attach it as a table in a Microsoft Access database.

1. Run GeoMedia or GeoMedia Professional and open a read-write connection to a Microsoft Access database.
   
   
2. Select Warehouse | Feature Class Definition.
   
   The Feature Class Definition dialog box appears.
   
   
   
3. Select the Access connection e.g. tmp. Click Attach.
   
   The Attach dialog box appears.
   
   
   
4. In the Type drop down list, select Excel 97. Click Browse and select the Excel spreadsheet containing the GPS readings.
   
   The selected spreadsheet name is displayed.
   
   
   
5. Change the target table name if you like. Click OK.
   
   The Excel spreadsheet is attached as a table to the Access database connection.
   
   
   
6. Now make sure the workspace coordinate system is Geographic WGS84 with EGM96 vertical datum. Select View | Coordinate System.
   
   The GeoWorkspace Coordinate System dialog box appears.
   
   
   
   
7. Click OK.
   
   
   
8. Select Analysis | Geocode Coordinates.
   
   The Geocode Coordinates dialog box appears.
   
   
   
9. In the Geocode attributes in field, choose the attached Excel spreadsheet table e.g. gps.
   
   
10. Click Coordinate System.
    
    The Coordinate System Properties dialog box appears.
    
    
    
11. Make sure the coordinate system is Geographic WGS84. In the Vertical datum drop down list, select Ellipsoid (geometric).
    
    
    
    
12. Click OK.
    
    
13. In the Longitude field, select the Excel spreadsheet column for longitude values e.g. lngdeg.
    
    
14. In the Latitude field, select the Excel spreadsheet column for latitude values e.g. latdeg.
    
    
15. In the Height field, select the Excel spreadsheet column for the GPS elevation readings e.g. gpshgt.
    
    
    
    
16. Click OK.
    
    The geocoded GPS points are displayed in the map window.
    
    

We have now corrected the GPS elevation readings. To verify this, just review the Z values of the point features.

1. Use the Select Tool command and click on one of the GPS points.
   
   The point is selected and shown in green.
   
   
2. Select Edit | Select Set Properties.
   
   The Properties dialog box appears.
   
   
   Note that the Z value shown is now the topograhic height i.e. the GPS reading minus the geoid height at that location.

Defining Geocoding Model for GeoMedia 6.1

In my previous post, I showed how to define a rule to parse 6-digits postal codes. The next step in setting up address geocoding in GeoMedia is to define the geocoding model. In this step of the workflow, there are two geocoding model types - roof top or center line (with left and right house number ranges) that you can choose to create. 

To make it easier to define the geocoding model, Intergraph has provided a hidden utility in the {GeoMedia}\Program\ folder. If you can't find it then you have to install the latest GeoMedia 6.1 hot fix 6.1.5.19 or later. In this post, we are going to define a roof top geocoding model that will transform 6-digits postal code strings from reference GeoMedia features into address indexes. At the same time, we will have to define the user prompts and the transformation of the 6-digits postal code strings entered by the user. We are going to make use of the 6-digits postal code parsing rule defined in the earlier post. 

Base Address Definition

Here you have to define the components that make up your addresses e.g. house number, street name, street type, postal or zip code, etc. In our simple example, we have only one component i.e. postal code. 

1. In Windows Explorer, double click the file DefGCM.exe in the {GeoMedia}\Program\ folder.
   
   The Define Geocoding Model Utility dialog box appears.
   
   
   
2. Click Base Address Definition.
   
   
   
   
3. Click the Add  button.
   
   The Base Address Element dialog box appears.
   
   
   
4. In the Address element name field, enter a meaningful name, e.g. postalcode. In the Address element description field, enter a meaningful description, e.g. 6-Digits postal code.
   
   Note: the description will be used later in the GUI of other address functions.
   
   The Base Address Element dialog box may look like this at this point.
   
   
   
5. Click OK.
   
   The new base address definition appears in the Define Geocoding Model Utility dialog box.
   
   
   
   
   

Define Address Transformations

There are two address transformations you have to set up. The first transformation to define is the transformation from the GeoMedia warehouse feature's address strings to the components (base address) of your addresses. The GeoMedia feature data is called the reference data here. For example, I may have a GeoMedia feature class named ADDRESS with an attribute field called POSTCODE that stores my postal code strings. I need to define how to map the POSTCODE field to the postalcode base address component.

The second transformation is the transformation from the address strings the user keys in to the base address components. For instance, the user may key in 123 or 123456;  I need to define the transformation that will map 123456 to the postalcode (base address) component.

1. Click the Address Transformation tab.
   
   The transformations entry fields for reference data and user addresses appear.
   
   
2. Click the Add  button for reference data.
   
   The Address Transformation dialog box appears.
   
   
3. Click the Add  button.
   
   The Address Transformation dialog box appears.
   
   
   
4. In the Address transformation name, enter a meaningful name, e.g. Postal code from database.
   
   
5. Click the Add  button.
   
   The Source Address Element dialog box appears.
   
   
   
6. In the Address element name field, enter a meaningful name, e.g. postalcode.
   
   Note 1: As we have only a single address element i.e. a 6 digits postal code, we can toggle on the This is a required address element option.
   
   Note 2: When you run the Publish to Address Geocoding Index utility, if you want it to automatically fill in the database field name for this address element, you can enter the database field name in the Suggested Name field.
   
   
7. Click the Add  button.
   
   The Suggested Name dialog box appears.
   
   
8. In the Suggested field name field, enter the database field name e.g. POSTCODE. Click OK.
   
   
9. Click OK to close the Source Address Element dialog box.
   
   The new source address definition is added to the Address Transformation dialog box.
   
   
10. Click the Direct Transformation tab. Then Click the Add  button.
    
    The Mapping Properties dialog box appears.
    
    
    
11. Toggle on Apply parsing rules. Click Browse.
    
    The Open Address Parsing Rules dialog box appears.
    
    
12. Browse and select the rules file we defined earlier (in my previous post) e.g. mypostalcode.xml. Click Open.
    
    
13. Click OK twice.
    
    The new address transformations for reference data definition is added to the Define Geocoding Model Utility dialog box.
    
    
14. Click the Add button  in the user address section.
    
    The New Address Transformation dialog box appears.
    
    
15. Toggle on Existing reference data address transformation. Select PostalCode from database and Click OK.
    
    The Address Transformation dialog box appears and the address definition from the reference data section is copied over.
    
    
    Note: instead of copying over the reference data definition, you can start from blank and create a new definition for transforming user addresses.
    
    
16. In the Address transformation name, enter PostalCode from user entry.
    
    Click OK.
    
    The new definition is added to the address transformation for user addresses.
    
    
    

Define Suggested Names (optional)

Suggested names are used by the Publish to Address Geocoding Index utility and GeoMedia's address geocoding functions e.g. Find Address. As the name indicates, Suggested Names are simply names that GeoMedia will use and find the matching feature classes and field names. If GeoMedia can't find the matching class/field, then the user will be prompted to select.

1. Click Suggested Names tab.
   
   
   
   
2. Click the Add  button.
   
   The Suggested Names dialog box appears.
   
   
   
3. In the Suggested feature class name, type in the name of the GeoMedia Warehouse feature class name that stores the reference addresses e.g. ADDRESSES.
4. Click the Add  button.
   
   The Suggested Name dialog box appears.
   
   
   
5. In the Suggested field name field, type in the name of the database field in the GeoMedia feature class, e.g. POSTCODE.
   
   
   
   
   
6. Click OK.
   
   The new suggested name is added.
   
   

Define Matching Indices

Here is where you can define how the user inputs will be matched with the geocoded address indexes. You can have sound like matching or the actual value matching.

1. Click the Matching Indices tab.
   
   
   
2. Click the Add  button in the upper half.
   
   The Matching Index Properties dialog box appears.
   
   
   
3. In the Matching Index name field, enter postalcode. Press OK.
   
   
4. Click the Add  button in the lower half.
   
   The Add to Matching Index dialog box appears.
   
   
5. In the Include the first characters of drop down list, select a number e.g. 3. In the Address element drop down list, select postalcode. In the Using method, select Actual Value.
   
   
   
   Click OK.
   
   
   
6. Select File > Save As and save the Geocoding Model definitions to an XML file, e.g. mypostalcode_gcm.xml.
   

The final setup step is to run the Publish Address Geocoding Index utility.

Simple example of defining parsing rules for geocoding in GeoMedia

Part of the workflow to setup GeoMedia geocoding functions to work is to define parsing rules to handle address conventions in your specific locality. Basically, the rules define how to break up an address string sequence into smaller parts - so-called tokens in GeoMedia geocoding terminology. For example, the string '123 James Street' can be parsed into the tokens house number '123', road name 'James' and road type 'Street'. 

As you can imagine, in real life the rules can be very complex in order to handle actual addresses. To aid in the rules definition process, GeoMedia comes with a hidden executable DefParsingRules.exe in the {GeoMedia product}\Program folder. The utility will save the rules as XML files that will be be used by GeoMedia's Publish Address Geocoding Index Utility to create the address geocoding index files (*.agi) . 

In this posting, I will show you how to use the Define Parsing Rules Utility to handle a simple example - 6 digits postal code strings. We will define a rule to output one 'postal code' token from input text strings. Perhaps in future I can post a more complex example. 

1. Run the Define Parsing Rules Utility by double clicking the DefParsingRules.exe in the GeoMedia's program folder.
   
   The Define Parsing Rules Utility dialog box appears. 
   
   
   
2. Click the Add button to add a new token.
   
   The Token dialog box appears.
   
   
   
3. In the Name field, type in a token name e.g. POSTALCODE. In the Type drop down list, select Pattern.
   
   Note: the postal codes are all digits and a simple regular expression pattern would be more than sufficient to detect the postal code from the input text strings. 
   
   At this point, the Token dialog box may look like this.
   
   
   
4.  Click the Pattern tab. In the Regular expression to match field, enter \d{6}. 
   
   Note: the \d{6} pattern will consider strings with 6 digits as postal codes. 
   
   The Token dialog box may look like this now. 
   
   
   
   
5. Click OK to close the Token dialog box.
   
   The new token is created and added to the Tokens list.
   
   
   
6. Click the Training Data tab.
   
   Note: you have to add in training data to 'train' the parser to detect the postal code strings. 
   
   
   
   
7. Click the Add button . 
   
   The Training Sample dialog box appears.
   
   
8. In the Sample text field, type in a representative postal code string e.g. 123456. Click Parse. 
   
   The Training Sample dialog box should like this.
   
   
9. If the Parsed token sequence list is still empty, then you can aid the training process by double clicking POSTALCODE in the Available tokens list. Click Parse again. 
   
   The sample text is parsed and added to the Parsed token sequence list.
   
   
   
10. Click Replace Training Sequence.
    
    The Training Sample dialog box should look like this. 
    
    
    
    
11. Click OK to close the Training Sample dialog box.
    
    Note: if the training is successful, the bottom right of the Define Parsing Rules Utility dialog box should show a neon green box with the Valid text. 
    
    
12. In the Define Parsing Rules Utility dialog box, click the Output tab. 
    
    
13. Click the Add button . 
    
    The Output Entity dialog box appears.
    
    Note: You have to define how you want to format the result tokens of the parsing. If you have multiple tokens, you can choose to have space, comma, or semi-colon separators. This dialog box is where it happens. 
    
    
14. Toggle on POSTALCODE in the At least one of the checked tokens must be present in this entity list. 
    
    
15. Click the Output Elements tab.
    
    
    
16. Click the Add button . 
    
    The Output Element dialog box appears.
    
    
17. Double click on POSTALCODE in the Available tokens list. Click OK.
    
    The Output Element dialog box should look like this.
    
    
18. Click OK to close the Output Element dialog box.
    
    The element is added to the Output Entity list.
    
    
19. Click OK to close the Output Entity dialog box.
    
    The Entity is added to the Output list.
    
    
20. Click the Testing Data tab.
    
    
    
21. You can now choose to test the rule against strings in text files, a database table, or a GeoMedia warehouse. In this example, we are going to test against a standard text file which has the contents shown below. As you can see, I have a few strings that satisfy the rule and some that don't. 
    
    
    In the File field, click Browse and select the text file.
    
    
    
22. Click Run.
    
    Note: The rule is applied against the selected text file and 2 entries appear in the Token sequences list - Unparsed and POSTALCODE as shown below.
    
    
    When Unparsed is selected, the Strings yielding the sequence list shows the unmatched strings from the test file such as 123, ABCDEF, 1234567. 
    
    When POSTALCODE is selected, the Strings yielding the sequence list shows the matched strings from the test file, all having 6 digits. 
    
    
23. Select File > Save As and save the parsing rules into an XML file. 

You have now created a parsing rule XML file which can be used later in the GeoMedia Publish to Address Index Utility.