I know I can use getCoordinateAt to retrieve the coordinates of a point at a percentage along a LineString, but I need to extract a segement of a LineString between start and end fractions as a new LineString.
Any pointers as to how to achieve this with OpenLayers 3?
Thanks
Related
I was wondering if anyone knows how to add an annotation to a polyline a certain distance from the start in iOS MapKit?
As you can see from the picture above (sorry for the bad drawing). I have drawn a polyline which is 100 miles long. Now I want to be able to add a map annotation at 13 miles along the line.
Is this something that is possible?
Any information would be greatly appreciated.
Thanks,
Dan
Treat your poly line points as a sequence of line segments. Start out with the target distance, 13 miles. Iterate over the points as line segments - .windows(ofCount: 2), compute the length of that line segment, if remaining distance is < line segment length, then your target point is the point that is 'remaining distance' from start of line segment in the direction of end of line segment. Otherwise, subtracting the line segment's length from remaining distance, until either you find your target or fall off the end of the poly line. The question of whether each line segment on poly line represents straight line (along map projection) or great circles (on surface of earth) is unimportant unless the distance between points is large.
Right now I am trying to understand the values within an ARKit transform matrix so I can quantify the movements of my SCNNode. From a previous post on stack overflow I have learned that the matrix contains information regarding the node's current translation, scale, rotation, and position.
What I am not understanding is which values are specifically associated with those four things. For example I have figured out that the first element of the 3rd column represents an X (horizontal) movement on the screen and the 2nd value of the 3rd column represents a Y (vertical) movement. But other than that I'm not sure what the rest of the values in the matrix mean.
Thanks for the help!
In a transformation matrix, the translation information is in the last column.
Given a transformation matrix, you can extract the translation from the last column as below:
let translation = SCNVector3(transform.columns.3.x, transform.columns.3.y, transform.columns.3.z)
Rotation and scaling use the first three columns and are more complex.
Scale is the length of the first three column vectors, and to extract the rotation you need to divide the first three column vectors by the scaling factors just mentioned.
You can refer to this link for a better understanding of scale and rotation and how to extract them.
MohammadRF's answered cleared things up for me the best. However, ARKit's matrices are in row-major order so if you were to transpose the matrices from the information he gave then it would apply to ARKit.
I need to calculate the minimum distance between a 3D point (latitude, longitude, elevation) and a line (defined as two points).
The elevation is not necessary on the ground, I need to consider flying objects.
I only found an article that explains how to do that on a generic space but my points are defined with lat/lon/altitude(meters).
Thank you for pointing in the right direction, in my case I need to do that in Javascript but couldn't find any library that takes into consideration the altitude.
Point-Line Distance--3-Dimensional
If you want to compare a 3d point to a 2d line, I suppose you mean a "line" on our earth, at elevation 0. Take a look at st_distance in postgis.
If I understand you correctly, that'll give you what you want.
https://postgis.net/docs/ST_Distance.html
Say I have the lines shown in the image below, represented in polar coordinate format (rho and theta). These lines are the output of OpenCV's HoughLines function after some post processing. (Sorry I'm not allowed to embed images yet.)
What I want to do is, given any one line, find all of the lines that are perpendicular to that line, as shown in the second image below.
I understand how to do this with Cartesian lines, but I'm having trouble wrapping my mind around what properties of rho and theta the two lines would have to have to be perpendicular, although I understand how polar lines work at least fundamentally. Sorry if this is elementary stuff, but I'm having trouble finding any explanation of this online anywhere. Do I need to first convert the lines to Cartesian coordinates, or is there some simpler way to do this? Any help would be much appreciated, thanks!
To get perpendicular lines in polar coordinates, you simply take the theta for the first line, and find all lines whose theta = +/- 90° of the first theta.
You have to normalize the angles to be within 0°-360° or some other range, when comparing them.
So if line 1 has a theta line1.Theta
Then the angle to another line is a = (line2.Theta - line1.Theta)
and you want all lines where a is close to -90°, 90°, 270°, -270°, ...
depending on how you normalize your angles
What I am trying to simulate here is random map generation. The random generation and computing is already done and stored in a 2D array of NSIntegers (about 400x400) where the value of each element represents the color of the tile on the map (ex: 1 = green, 2 = blue). What I want to do is display the 2D array as a colored grid on the user's screen.
I am having trouble figuring out the right way to do this. Options I have considered are drawing points with UIImage and drawing 1pt rectangles with CGRect.
What is the best way to do this? Code samples would be very helpful here.