# Sampling methods in curvilinear swath profiles

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## Geology

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## Sampling methods

There are two main approaches for sampling parameters of interest along curvilinear features. These approaches differ from each other by the way sample points are stacked. Here we consider the elevation as the parameter of interest and DEM as the input data used for the sampling.

1- Orthogonal line

In this approach, elevation is sampled at equal-distant points along lines orthogonal to the midline. This approach has the advantage of knowing the angle, hence the direction, of orthogonal lines. On the other hand, it has two disadvantages. First, not all pixels of DEM are included in sampling, then in evaluation. Second, around curved parts of the curvilinear features over-sampling or under-sampling happens. Over-sampling or under-sampling happens where orthogonal lines converge or diverge at the concave and convex sides of the midline, respectively.

2- Parallel signed distance line

In this approach, elevation is sampled along lines that are parallel to the midline. Each of these parallel lines has a constant signed distance from the midline. Since the stacking of elevation values is along lines that are parallel to the curvilinear feature, the stacked values do not include directional information. In contrast to the previous method, using this method prevents the over-sampling and under-sampling problems, because each elevation point includes in the sampling only one time.

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