How do I generate a DTM using image fan statons?

Select from the 3DM CalibCam menus: Digitising Tools | Generate DTM from Stations.

Create DTMs by Station Pairs

  • Ensure the Project Type is set to Station Pairs.

  • Select the two appropriate image fan camera stations which will be used to create the DTM. The camera stations are selected from the dropdown boxes highlighted in the green rectangles in the above dialog. Press the Add/Update button, the DTM name will display in the list with its corresponding camera stations.

  • Under Project Type again, press the Select Area button. A dialog will pop up showing the coverage area of the selected two camera stations, the DTM will be generated from this coverage area and will be generated in tiles displayed by the mustard green rectangle(s). Zoom out on the entire coverage area by using your mouse scroll wheel. You can optionally adjust the coverage area by altering the mustard green rectangle boundary by using the corner nodes:

Select DTM Area on Station Pair

Once the coverage area has been set, press the OK button to accept.

DTM Generation Settings

Check the DTM Settings are set up to requirements.

Create DTMs by Station Pairs

Match Similarity

This value indicates the correlation threshold in order to accept or reject a potential DTM match point. 0.8 (or 80% confidence in the potential match) is a good default value to use.

Match Window Size

This is the size of the window the software uses when matching pixels, 21 pixels is a good default to use.

Density

This setting is used to filter the DTM points. In the dialog above, the software will nominally try to create a DTM point every 8 × 8 pixels.

Max. Image Size

This is the maximum size of each texture generated, DTMs will be broken up into tiles (as displayed when the Select Area button is pressed) to ensure the texture remains within this limit. Reduce this value if your PC is running out of memory (or crashing) when generating the DTM. More tiles of smaller size will be created, but will be less onerous for your PC to process. You can check to see how many DTM tiles will be created by pressing the Select Area button again.

Minimum Spacing

Filter points during merge to ensure points are at least this distance (ground units) apart.

There is an option to check the Use average spacing checkbox, the software will calculate the average level of detail of the original DTMs in order to make the final surface close to uniform.

  • Check the Disable Redundant Images checkbox if the image fans have large overlaps between adjacent images taken for the image fans. This will speed up the process by removing redundant images for the DTM generation.

  • Click the Create button to generate the DTM tiles for the camera station pair, once complete the software will display the total points generated and the processing time.

You can now exit 3DM CalibCam and load the DTM tiles in 3DM Analyst for capture.