Thursday, September 24, 2009

Digitizing New Lines with Global Mapper

I have always used Global Mapper mostly as a viewer and converter for GIS files. Recently I tried out the digitizing commands on Global Mapper 10 and 11 and I found them to be surprisingly competent and powerful to create and edit point, line, and polygon vector features. Version 11 has some improvements over Version 10 - the most notable one being the new Digitizing toolbar, which is not available on the older version.

To use the digitizing functions, you have to enter digitizing mode by clicking the Digitizer Tool button in Global Mapper.

In Global Mapper 11, the Digitizer Toolbar will appear as shown below.

And the screen cursor would change to a cross hair with a EDIT label at the bottom.

A right click in the map display would bring up a context menu as shown below.

If I want to create a new line feature, then I would choose Create New Line Feature in the pop up context menu. The screen cursor label would change to the string "LINE".

As shown in the screen shot below, I can Left-click with the mouse button to place consecutive points of the line feature.

To complete the placement of the new line feature, Right-click with the mouse button. Then the Modify Feature Info dialog box will pop up.
In the Feature Type drop down list, you can choose any pre-defined feature type e.g. River, Unknown Length. Or create your own type by clicking the Create New Type button.
You can choose to place the new line on an existing layer or a new layer by choosing <Create New Layer for Feature> in the Feature Layer drop down list.
After you click OK, it will prompt you for the new layer name. Just type in a new name e.g. Rivers and click OK.

Your new line feature is created and placed in the layer you want.

Tuesday, September 15, 2009

Lidar LAS file conversion to Tiff using FME

I tried out using Safe FME to convert a Lidar LAS file to a grayscale TIFF image file and I was reasonably successful doing it. I'm not quite completely happy with it ( for instance, it would be more correct to filter out all returns except the first return) but here are the steps that I took.
  1. From the FME Workbench, create a translation using the translation wizard. Choose ASFPRS Lidar Data Exchange Format (LAS) as the source dataset. Click Next.

  2. When prompted to specify the location of the source data, browse and select the input LAS file, e.g. Serpent Mound LAS Data.las. Click Next.

  3. When prompted to Select Destination Format, choose GeoTIFF (Georeferenced Tagged Image File Format). Click Next.

  4. In the Select Feature Types dialog box, toggle off header and variable_length_header feature types if you like because we are only interested in the point feature type. Click OK.

  5. Within the workbench, drag and drop the transformers ExpressionEvaluator, Concatenator, and ImageRasterizer onto the workbench. Connect them up with the source and destination datasets as shown in the figure below.

  6. Open up the ExpressionEvaluator transformer's Properties. In the Expression field, type in @Value(Intensity). Click OK.

    Note: the output from this transformer is the attribute _result by default.

  7. Open up the Concatenator transformer's Settings dialog box. Form the string "_result, _result, _result" in the Concatenated Items box. In the Destination Attribute field, change the text to fme_color. Click OK.

    Note: in this step, we are forming the rgb string. Since intensity images are grayscale, we simply repeat the same intensity value in the red, green, and blue parts of the output fme_color string.

  8. Open up the ImageRasterizer transformer's Parameters dialog box.

  9. In the Rows/Columns or Cell Size field, choose CellSize.

  10. In the X Cell Spacing and Y Cell Spacing fields, type in the desired TIFF pixel size e.g. 1 m.

  11. In the Interpretation Type field, choose Gray8. Click OK.

  12. Run the translation.

    The intensity image is created from the source LAS file.

    The resultant intensity image isn't too bad but as I said earlier, the process can be improved. Maybe next time...

Thursday, September 10, 2009

Select and update feature attributes in GeoMedia

In GeoMedia, there is a useful function to select one or more geographical features and update their attributes but it is hidden away under some pulldown menus. Sometimes it is easier for users to use the Selection tool and simply point and click to select features for updating.

In this example, I want to update the STATE_NAME attribute of the Counties feature to e.g. Alabama. Here are the steps:
  1. In GeoMedia, click the Selection Tool button.

  2. In the map view, click on one or more Counties feature.

    The features are selected (in green color).

    Note: Press CTRL + click to add more features to the selection set.

  3. Select Edit > Attribute > Update Attributes.

    The Update Attributes dialog box appears.

  4. In the Update Features In box, expand the Select Set node. Expand the Warehouse node. Select the Feature name, in this example, it is Counties.

    The attributes of the selected feature are displayed in the Attributes to Update box.

  5. In the Attributes to Update box, scroll to the attribute(s) you want to update e.g. STATE_NAME and type in the new value e.g. Alabama.

    At this point, the Update Attributes dialog box may look like this.

  6. Click Apply.

    The selected features are updated with the new attribute values.

  7. Close the dialog box.