Combine or analyze two terrain models

In Pythagoras you can generate a third terrain model based on two existing ones. This is useful for volume calculations, design comparison, stockpile analysis, or merging sub-areas.

Use the function DTM > Combination of 2 terrain models...
You have four processing options:

• Difference – height difference between two models

• Maximum – keep the highest points

• Minimum – keep the lowest points

• Union – merge the two models

Note: This process never changes your original terrain models. A new third model is always created.

WORKFLOW

Prepare two DTMs in your file

Create separate DTMs first:

• One model is usually the existing terrain (e.g. survey).

• The other is a design model or a second survey (e.g. after execution).

Make sure each DTM is named clearly and is visible.

Go to DTM > Combination of 2 terrain models

In the Combine 2 terrain models window:

• Enter the name of the new terrain model.

• Select DTM 1 (e.g. the existing terrain).

• Select DTM 2 (e.g. the design model).

• Choose the processing method:

Difference: calculates height differences in the overlapping area. Order matters: DTM1 – DTM2 defines whether the result is positive or negative.

Maximum: keeps the highest Z-value for each XY-point.

Minimum: keeps the lowest Z-value for each XY-point.

Union: merges all points from both models into one.

• Click OK.

Result: A new terrain model is created based on the selected method. The original models remain unchanged.

Typical applications

Difference

Calculate elevation differences between two models.

Example:

Compare terrain before and after excavation to determine cut/fill volume.

Related articles:

How to create a Cut and Fill map (basic)

How to create a Cut and Fill map (advanced)

Maximum

Create a terrain model based on the highest Z-value at each XY-point.

Example:

After adding soil, use Maximum to model only the raised areas.

Minimum

Create a terrain model based on the lowest Z-value at each XY-point.

Examples:

• Visualize trenches or basement levels.

• Check excavation depth against design floor to confirm sufficient depth.

• Combine with a difference analysis to detect exact shortfalls.

Union

Merge two terrain models into one larger model.

Example: 

Combine several surveyed zones into one global DTM for analysis or presentation.

Important:

• Existing gaps (empty zones) are not automatically filled.

• If gaps in both models touch, they can form a larger hole.

• To add extra parts into an existing model, use DTM > Edit terrain model: Insert.

Best practices

• Give each terrain model a clear layer name and color.

• Document what each model contains (e.g. field survey, design, stockpile).

Useful for:

• Delivery of cut/fill projects.

• Estimating stockpile volumes (design + stockpile).

• Providing contractors or engineering firms with a single model file.