# Constraint: PTdSF

Model ElementThe Constraint_PTdSF element constrains a fixed point on a body to slide along a surface that passes through the origins of a specified set of markers.

## Description

These markers may belong to different bodies. As the markers move in space, the surface is calculated at every time step using CUBIC spline interpolation through the marker origins. Hence, the surface deforms as the markers move about.

## Format

<Constraint_PTdSF
id                   = "integer"
[ label                = "string" ]
i_marker_id          = "integer"
ref_dsurface_id      = "integer"
/>

## Attributes

id
Element identification number, (integer>0). This number is unique among all Constraint_PTdSF elements.
label
The name of the Constraint_PTdSF element.
i_marker_id
Specifies a Reference_Marker whose origin defines the point that is constrained to move along the deformable curve.
ref_dsurface_id
Specifies the deformable surface used to define the Constraint_PTdSF element.

## Example

<Reference_DeformSurface
id                  = "1"
end_type            = "NATURAL"
num_marker_row      = "7"
num_marker_col      = "7">
30101490 30101500 30101510 30101520 30101530 30101540 30101540
30101420 30109781 30113791 30117801 30121811 30125821 30101480
30101350 30108711 30112721 30116731 30120741 30124751 30101410
30101120 30102061 30103071 30104081 30105091 30106101 30101130
30101140 30110571 30114581 30118591 30122601 30126611 30101200
30101210 30111641 30115651 30119661 30123671 30127681 30101270
30101280 30101290 30101300 30101310 30101320 30101330 30101340
</Reference_DeformSurface>

<Constraint_PTdSF
id                  = "1"
i_marker_id         = "30107780"
ref_dsurface_id     = "1"
/>

<Post_Graphic
id                  = "500000"
type                = "DeformSurface"
surface_id          = "1"
nseg_u              = "30"
nseg_v              = "30"
/>