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Step 4Control Points
Understanding control points:
Control points are what the optimizer uses to determine the relationships between all the images in your panorama. There are actually two different kinds of control points. Normal control points identify two points in two different images that refer to the same object, and therefore should appear at the same place in the final panorama. Horizontal and vertical line guides identify two points that should be in a straight line, usually from the same image (panoramas will sometimes appear wavy without them). Control points are the main inputs that the optimizer uses to align the images into a complete panorama, and the difference between a good panorama and a bad one depends on the quality of control points you create (and how much time you spend on them).
Before you can add control points, you need to add all source images to your project. Use the "Load images" button on hugin's Assistant tab to do this. If you have autopano installed, hugin will probably run it immediately and attempt to optimize the panorama as soon as it finishes and give you a preview of the whole panorama. If you want to add your control points all by hand, turn this option off in hugin's preferences.
Now switch to the control points tab. This screen shows two images side by side so you can edit the control points that belong to them. Use the menus above the images (or numbered tabs in older versions of hugin) to select the first and second images (0 and 1). Find an recognizable object that appears in both images, preferably something near the background. Click on part of it in the left image. The image window should zoom in all the way showing the area around where you clicked. Then click the same part of the same object in the right image. Hugin will perform a "fine tune" as soon as you click the second image, searching for a point that matches the first image best. You can drag either of the control points to a new position if they're not in the right place. Clicking the fine tune button at any time will snap the right point to the part of the image that's most similar to the left point. Once both points are in the correct place, right-click to save the control point.
To successfully align your panorama, each overlapping pair of images needs to have at least one control point. Usually one isn't enough (since the images can still rotate about the common point), so try to add as many as you can find. If the images have objects in the foreground and background, you won't be able to align both planes if there is any parallax error. Background points usually work better, so add control points only on far away objects if you can see nearby objects in different places in the two images.
To add a horizontal or vertical line guide, select the same image in both windows. Find an object, such as a lamp post, the side of a building, or part of the horizon, that you want to appear as a level horizontal or vertical line in the final image. Place a point in the left window at one end of the line, and a point at the other end in the right window. Fine tune tends to get confused with lines, so you may have to move the points around manually. Right-click to add the control point. The mode menu below the control point list should indicate that it is a vertical or horizontal line. Change it to the correct mode if hugin guessed the direction wrong.
After you have enough control points, you can optimize the panorama to place each image in the right position and get a preview of the final result.
Control points are what the optimizer uses to determine the relationships between all the images in your panorama. There are actually two different kinds of control points. Normal control points identify two points in two different images that refer to the same object, and therefore should appear at the same place in the final panorama. Horizontal and vertical line guides identify two points that should be in a straight line, usually from the same image (panoramas will sometimes appear wavy without them). Control points are the main inputs that the optimizer uses to align the images into a complete panorama, and the difference between a good panorama and a bad one depends on the quality of control points you create (and how much time you spend on them).
Before you can add control points, you need to add all source images to your project. Use the "Load images" button on hugin's Assistant tab to do this. If you have autopano installed, hugin will probably run it immediately and attempt to optimize the panorama as soon as it finishes and give you a preview of the whole panorama. If you want to add your control points all by hand, turn this option off in hugin's preferences.
Now switch to the control points tab. This screen shows two images side by side so you can edit the control points that belong to them. Use the menus above the images (or numbered tabs in older versions of hugin) to select the first and second images (0 and 1). Find an recognizable object that appears in both images, preferably something near the background. Click on part of it in the left image. The image window should zoom in all the way showing the area around where you clicked. Then click the same part of the same object in the right image. Hugin will perform a "fine tune" as soon as you click the second image, searching for a point that matches the first image best. You can drag either of the control points to a new position if they're not in the right place. Clicking the fine tune button at any time will snap the right point to the part of the image that's most similar to the left point. Once both points are in the correct place, right-click to save the control point.
To successfully align your panorama, each overlapping pair of images needs to have at least one control point. Usually one isn't enough (since the images can still rotate about the common point), so try to add as many as you can find. If the images have objects in the foreground and background, you won't be able to align both planes if there is any parallax error. Background points usually work better, so add control points only on far away objects if you can see nearby objects in different places in the two images.
To add a horizontal or vertical line guide, select the same image in both windows. Find an object, such as a lamp post, the side of a building, or part of the horizon, that you want to appear as a level horizontal or vertical line in the final image. Place a point in the left window at one end of the line, and a point at the other end in the right window. Fine tune tends to get confused with lines, so you may have to move the points around manually. Right-click to add the control point. The mode menu below the control point list should indicate that it is a vertical or horizontal line. Change it to the correct mode if hugin guessed the direction wrong.
After you have enough control points, you can optimize the panorama to place each image in the right position and get a preview of the final result.
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