investigating EXP Cursor Snap Jumps to Non-EXP Target Position

[Frederf]

I find that when "snap" cursor to target in EXP that the cursors will move to where the target would be in the non-expanded display instead of where the target is in the expanded display.

 

E.g. if the target is 80% from the bottom of the display non-expanded and the cursors are placed over the target in expanded mode the cursor moves to 80% from the bottom of the display. Of course since the target will be in the middle of the display when the EXP mode is centered the cursors seem to jump "above" the target when range is >50% of the non-expanded scale and jump "below" the target when range is <50% of the non-expanded scale.

 

This makes snapping cursor to target in EXP impossible.

F16EXPsnap.trk

[BIGNEWY]

Hi, 

 

thank you for the track, but do you have any evidence it should be any other way? I can find no reference for this.

 

thank you

[Frederf]

There isn't a document I know of which will specifically state "in expand mode the cursor snap snaps the cursor to where the track is not to where the track would be displayed if it wasn't in expand mode." It just does because that's what snapping the cursor to the track means. Expanded or not it just puts the thing on the thing.

 

Slewing the cursor is done in real coordinates, e.g. azimuth and range, in both NORM and EXP. The FCR display has screen space coordinates but that's irrelevant. For example if the object on the scope is at 17° left, 32nm range and the cursor is at 21° left, 29nm range then let's say that's outside the snap radius. The cursor is slewed to 17° left, 32nm range and the system snaps the cursor to the track. The system is going to snap the cursor to that track at 17° left, 32nm range. It doesn't matter if the display is NORM or EXP. It doesn't matter where on the grid of screen pixels this corresponds to.

 

DCS is doing most of the steps right. When the cursor gets within proximity of the target it detects "a ha, I should snap cursor to track Z!" The issue is that the code is asking "OK, where in screen space should I put the cursor in order to overlay on track Z?" and the code is telling it the wrong position. It's saying "oh yeah, for track Z put the cursor at X, Y on the MFD." Unfortunately the X, Y screen space position is not appropriate for the expanded mode (it's the X, Y for NORM). The correct cursor placement in screen space when in EXP to snap to track Z is some different math. All that's needed is a new bit of code that returns the correct screen space for cursor placement when snapping in EXP.

[BIGNEWY]

Hi Frederf,

 

without seeing some evidence I can not ask the team to change it. 

 

I will speak to the team however. 

 

thank you

[WHOGX5]

[WHOGX5]

For the love of god, I wrote an entire post, and then it only sent the pictures. Oh well, I'll recap it in short.

 

First of all, I think you've misunderstood the issue BIGNEWY. The pictures you see above show a locked contact both in NORM and EXP mode. When EXP mode is entered, the contact moves to the center of the display instead of staying in the same location. It's not even inside the radar beam. Also, if I move my cursor over the contact in EXP mode and press TMS UP, it won't select the target. However, if I place the contact in the center of the display while my cursor is elsewhere, then I can select the contact. This is obviously inaccurate.

 

If you need reference materials, here is a video of an early F-16C entering EXP mode (at 5:39):

 

https://youtu.be/Aq5HXTGUHGI?t=339

 

As you can see, when EXP mode is selected the screen zooms in on the locked contact. If you have no contact selected, then the display will simply zoom in on your cursor.

 

The reason the selected contact/cursor stays in the same location both in and out of EXP mode is so that you always know the contact/cursors position in relation to your radar gimbal limits. If a locked contact is 2 centimeters from the right edge of the display in NORM, then that same contact will be 2 centimeters from the right edge in EXP mode. So if you don't have a contact locked and have your cursor close to it but not on top of it, then the cursors location will be accurate relative to the radar gimbal limits, but the contact will have shifted out of position due to the zoom level.

Edited February 14, 2021 by WHOGX5

[Frederf]

The snap moving the cursors to the wrong part of the display and the EXP view not being centered on the cursor when expanding are different but possibly related issues.

 

Fundamentally EXP doesn't change the cursor at all. Instead it expands the radar picture 4:1 so that the entire radar picture won't fit on the MFD. If the cursor is 13% right of center is the display in NORM and EXP is commanded the cursors are still 13% right of center in the expanded display. All radar objects at this horizontal position in NORM will remain in that horizontal position in EXP. Objects which are for example 10 pixels to the right of cursor in NORM become 40 pixels to the right of cursor in EXP. The same is true for 10 pixels to the left becoming 40 pixels to the left. It is said the expansion occurs about the cursor.

 

This is an example NORM radar display. I have given the radar picture a sort of texture to help illustrate what happens under expansion.

This is what DCS does. The central dot that was previously under the cursor is moved to the center of the display.

This is what DCS should do instead. The location under the cursor remains under the cursor after expansion. Everything on the radar picture is 4x as far away from the cursor as it was in NORM.

This is what happens when slewing in expanded mode. The radar picture will appear to move in the opposite direction as the cursor at a 3:1 ratio. The position of the cursor may be read directly in terms of azimuth and range in the exact same way against the blue tic scale along the bottom and left edge in both NORM and EXP. The only major difference in EXP is the scale of the radar picture and the fact that only 1/16th of it is visible on the MFD at once.

 

I estimate when the EXP mode is changed to conform to the above concepts the issue of cursors snapping away from targets in EXP will solve itself.