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h2. Introduction

The seismic interpretation tool lets you interpret horizons, faults and observations. This can be done both manually and automatically. In your Geocap project you will typically have an interpretation folder with one or more *Ihorizon* datasets, one *Faults* folder and one *Observations* folder.

The structure of a horizon in Geocap is as follows:
* One horizon can contain interpretation for several seismic lines
* Each line can have many segments
* Each segment can have many picks

This means that each horizon will normally contain thousands of picks along different seismic lines. Each pick is stored with the following information:
* Time value
* Seismic line name
* Shot point

The way Geocap stores its horizon data is compatible with most other seismic interpretation systems.

The seismic interpretation tutorial is found in the Shelf section [Seismic Interpretation|tut:L. Seismic Interpretation].

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*In this section:*
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h2. Importing interpretation from external files

To import an existing interpretation from file, create an *Interpretation* folder and then right-click on the *Interpretation* folder and select *Import > Interpreted Horizons*. The external file must be on ASCII format with one pick per line. Each pick must contain position and shot point in addition to the name of the corresponding seismic 2D line.

An Import dialog appears. You'll most likely need to *Adjust header* and change *File column* for *X*, *Y*, *Time*, *SP*, and *Data separator*. Take a moment to inspect the *Data separator*. This should be the name of the corresponding seismic 2D line. The remainder of the panel settings are usually kept as is.

Read about how to import interpreted horizons in the import chapter [ug:Importing Interpretation]. There all technical details are explained.

h2. Interpretation data structure

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During interpretation (or import) a dedicated interpretation data structure is created. The base folder is an *Interpretation* folder. An *Interpretation* folder contains subfolders and *IHorizons*. An *IHorizon* (i.e. _Interpreted Horizon_) is the parent for any number of *Pick Group{*}s. Each *Pick Group* represents the interpretation of current horizon on a seismic line. The name of a *Pick Group* must and will be exactly the same as the corresponding seismic line.

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!att:_img_menu^pm_interpretation.jpg!
_Interpretation data structure_
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h2. Interpretation interface

The seismic interpretation tool can be found under *Tools > Seismic Interpretation*.

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_The interpretation menu_


h2. Interpreting horizons

Use the *Seismic Control* tab when interpreting horizons. In the *Data* section you can browse in new interpretations and horizons or you can create new ones. The *Edit* button lets you change the properties and graphical settings of interpretations and horizons. You can display horizons in the graphical window directly from the interpretation menu without using the regular commands.

Before you can start interpreting you will have to select the seismic line you want to interpret on. Do this by displaying one or several seismic lines from the project and then use the *Select* button in the interpretation menu and click on the one you want to interpret.

*{+}Manual interpretation{+}*

Select the *Snap mode* you want to use. Geocap can snap to either max (peak) or min (trough) or none of them. Using the snap mode will help you increase the precision when interpreting. When you have set the tracking parameters click the *Start interpretation* button and start digitizing with *P* along the horizon. Click the *Stop* button to stop the digitizing.


*{+}Automatic interpretation{+}*

Geocap can track a whole seismic line automatically. This saves a lot of time when dealing with strong continuous reflectors. Select a snap mode and set the track mode to *Auto*. The delta Z value will constrain the auto-tracker to a time interval it is allowed to "jump" between each shot point. Click the *Start interpretation* button, point your mouse on the line you want to interpret, press *P* and Geocap will interpret the whole line.

You can also partially auto-track a line using the *Insert* tracking mode. Click the *Start interpretation* button, point your mouse where you want to start the interpretation, press *P* and the point the mouse where you want to end the automatic interpretation and press *P*. Geocap will then interpret this segment automatically.


*{+}Edit or erasing interpretation{+}*

You can edit the interpreted line by clicking the *Start interpretation* button and simply re-digitize the section you want to edit. Geocap will automatically update the line when you click the *Stop* button.

There are three options for erasing segments of an interpreted line:
* *Between 2 picks* \- Use *P* to select which points to delete between
* *Between beginning and pick* \- Use *P* to select end point.
* *Between pick and end* \- Use *P* to select start point.

Use the *Erase* button to start erasing.

h2. Interpreting faults

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h2. Interpreting observations

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