Grid and Meta Grid

[Chips&Chips]

I already spent a half hour asking this only to be LOGGED OUT. I am not going to go through all the "required stuff" mentioned above again. Just my question.

EXACTLY what is the relationship between GRID and META GRID? What is a META GRID and how does it function?

And, once I have the grid/meta grid that I need, how do I ensure that the center of a circle snaps to that grid.

Details: My first drawing in QCAD

It is a 6" x 3.5" circuit board.

I have an outline that seems to be snapped to the 0.1", default and automatic grid.

I need the holes at 0.150" x 0.150" from the corners of that outline. I am using a second layer for them.

I set the grid to 0.1 and the meta grid to 0.25. That seemed to give me a 0.1" main grid with four sub-divisions.

But my circles do not snap to the sub-divisions. Grid smap icon is ON.

HELP!

[CVH]

Hi,

A grid is a rectangular pattern of dots and/or lines that covers the entire XY plane.
It is an overlay and will not be printed.
In QCAD the dots are the Grid points and the lines are the Meta Grid.
One can however prefer to format the Grid as solid lines: menu View .. Application Preferences .. Graphics View .. Grid.
Common is to set the Meta Grid up as N number of grid steps with for N an integer.

One can not snap to the Meta Grid unless this coincides with a whole number of grid steps, it is a visual aid.
Using a Grid 0.1 and a Meta Grid 0.25 then the Meta Grid will coincide with the Grid each 5 grid steps.
The Meta Grid may cross halfway between grid step 2 and grid step 3 but this crossing is not a Grid snap-point.
Remark that there is a known bug when using values not based on 1*10^n, perhaps only for metric users.

Snapping to the Grid is by default and you can turn that off/on temporary and even permanent.
Auto snapping options are configurable under: menu View .. Application Preferences .. Snap .. Auto snap.

Snapping tools can be found under menu Snap.
When indicating a position required by a tool then the snapping methods are displayed/activated by default.
Auto snapping is default but you can select to use another type of snap-point for each coordinate that is required.
Grid, intersection, endpoint, reference, ...
While snapping it is mentioned by an auxiliary text to what type of point is snapped.

Drawing with the Grid is possible but also limited to how it is defined.
On top, the Grid/Meta Grid is always aligned in XY with the drawing origin (0.0, 0.0)
Designers usually draw with the use of absolute or relative positions or with the use of auxiliary construction lines.
For the 4 holes one can easily draw 4 parallel lines at 0.150 units and use the intersections as center positions.
Deleting the auxiliary construction lines afterwards.

Regards,
CVH

[Chips&Chips]

Thanks for the timely reply. I do appreciate it.

If I understand this;

Things can ONLY snap to the Grid. Never to the Meta Grid unless it corresponds to a GRID location.

So it is not very useful to try to divide the Grid by using the Meta Grid.

It would be more useful to set the Grid to your smallest snap distance and then use the Meta Grid to add lines on top of the Grid, at a LARGER distance than the Grid spacing.

Stated another way, in QCAD the Meta Grid is what most CAD programs refer to as the Grid. And the Grid in QCAD is what most other CAD programs refer to as sub-divisions of their Grid. I think stating it that way would get most people who are coming over from other CAD programs on board faster.

In my situation, where I need 0.050" spacing I could set the Grid to 0.050" and the Meta Grid to a larger spacing, like 0.500", for instance. I am going to try that.

Paul A.

[CVH]

Things can ONLY snap to the Grid. Never to the Meta Grid unless it corresponds to a GRID location.

Indeed, you are actually snapping to the Grid if that coincides with the Meta Grid.

In my situation, where I need 0.050" spacing I could set the Grid to 0.050" and the Meta Grid to a larger spacing, like 0.500", for instance. I am going to try that.

Additionally you can consider to use a fixed Grid/Meta Grid.
See: menu View .. Application Preferences .. Graphics View .. Grid.
Uncheck automatic scaling.

The Grid/Meta Grid will not adapt to the viewport zoom stated.
When zooming out the Grid's may disappear when less than N(=10) pixels apart.

Regards,
CVH

[Chips&Chips]

Thanks on the suggestion on turning off auto grid scaling. I like that, at least for the present.

But another question about the grid/meta grid, if you don't mind. I thought I had drawn an outline rectangle that was 3.5" x 6" yesterday. But today it was 35" x 60". Was I mistaken about the size of what I drew, or did my changes to the grid and meta grid settings somehow change the dimensions of my outline?

This could be important because, in the past with other CAD programs, I have often changed the grid spacing in the middle of a drawing. I am working on another drawing in FastCAD right now and I have changed the grid spacing many times in that drawing: 0.1", 1/8", 1/16", 0.5", 1", even 1/32". It has been all over the map. But the dimensions of the drawn objects have always remained the same. If QCAD changes the dimensions when the grid is changed, that could be a very important thing to keep in mind.

[CVH]

Was I mistaken about the size of what I drew, or did my changes to the grid and meta grid settings somehow change the dimensions of my outline?

The grid settings will not affect drawing entity sizes, the Grid is an overlay.

Did you determine the original/new size by Grid, by Property Editor, by Info tools or with a Dimension.

When adding dimensions ensure that the Scale option is 1:1 or 1.

The Option Toolbar is usually directly above the drawing panel and is shared by most QCAD tools and methods.
Always have an eye open for tool options ...

Regards,
CVH

[Chips&Chips]

Not completely sure how I drew that original rectangle. I thought I select Rectangle with dimensions and typed in 3.5 and 6. I did have the units set to inches. But I must have done something wrong.

The new outline is OK and I am making progress. Screen shot attached.

Untitled.jpg (934.72 KiB) Viewed 1718 times

I am seeing another odd thing with the grid. I have been working with it set at 0.050". If I zoom out too much, it no longer snaps to that value when the dots disappear. Is that normal? Does the grid snap only work with grid dots that are actually visible? Or do I have some setting messed up?

Thank you, once again.

[CVH]

it no longer snaps to that value when the dots disappear. Is that normal?

Figures, without a displayed Grid there are no grid snap points.
At some point it may become very hard to navigate that precise in the model.
We are talking about less than 10 pixels using defaults.
Without a limit the screen may become filled with nothing but Grid dots.

The Rulers may turn empty too.

Regards,
CVH

[Chips&Chips]

Sooo.....

I am a simple person. And I thought my question was simple.

You say, "Figures, without a displayed Grid there are no grid snap points."

So, are you saying that YES, the grid points must be visible in order to snap to them? And when they disappear due to being too close to each other, then nothing can snap to them?

But, here's another observation. The grid points not only disappear when they become too close together, which makes sense and is also followed by every CAD program I have ever used, BUT they also disappear when I zoom OUT IN and they become widely spaced. It appears that the grid points have an actual size and when I zoom out their screen image becomes smaller and smaller until they disappear. Is that normal in QCAD? I have never seen that behavior in any other CAD program. And can I still reliably snap to them at that point?

I would think, when grid snap is selected, the code would search for the nearest grid point using mathematical means, not visibility on the screen as the criteria.

Perhaps there is a setting that I am unaware of? Or could it be my monitor?

Edit: Correct "OUT" to "IN".

it no longer snaps to that value when the dots disappear. Is that normal?

Figures, without a displayed Grid there are no grid snap points.
At some point it may become very hard to navigate that precise in the model.
We are talking about less than 10 pixels using defaults.
Without a limit the screen may become filled with nothing but Grid dots.

The Rulers may turn empty too.

Regards,
CVH

[CVH]

But, here's another observation. The grid points not only disappear when they become too close together, which makes sense and is also followed by every CAD program I have ever used, BUT they also disappear when I zoom OUT and they become widely spaced.

You probably mean zoom IN ... Zooming out a fixed grid gets compacter ... Zooming in a single grid step may exceed the screen size.
You wrote earlier:

Thanks on the suggestion on turning off auto grid scaling. I like that, at least for the present.

Regards,
CVH

[Chips&Chips]

It was late and I was tired. Yes, I did mean zoom IN.

I start with Imperial, and Inch units for both Drawing and Page units.
I set the Grid to 0.05" for both X and Y.
I set the Meta Grid to 0.5" for both X and Y.
My screen view covers about 7" wide by 4" high.
And I can see the Grid dots and the Mega Grid (lines by my choice).

THEN I zoom IN.
The Grid dots and Mega Grid lines become wider spaced.
I zoom IN more and the Mega Grid lines stay very nicely visible.
BUT the Grid dots become less and less visible with every click of the mouse wheel.
And at some point the Grid dots become totally invisible.

I have tried a number of background and Grid dot colors but always the same. The Grid dots disappear.

OK, I took some screen shots and blew them up. And the Grid dots were there. Just too small to be seen. I need to look at this some more. It's late again so, tomorrow.

But, here's another observation. The grid points not only disappear when they become too close together, which makes sense and is also followed by every CAD program I have ever used, BUT they also disappear when I zoom OUT and they become widely spaced.

You probably mean zoom IN ... Zooming out a fixed grid gets compacter ... Zooming in a single grid step may exceed the screen size.
You wrote earlier:

Thanks on the suggestion on turning off auto grid scaling. I like that, at least for the present.

Regards,
CVH

[andrew]

Perhaps just an illusion? Grid dots are more visible when close together than when far apart.

Can you compare two grid dots from two screenshots (zoomed in and zoomed out).

[CVH]

And I can see the Grid dots and the Mega Grid (lines by my choice).

The Meta Grid is always displayed as lines.
The Grid are dots or lines by preferences.

And at some point the Grid dots become totally invisible.

When you set certain values for Grid and Meta Grid then these values are also considered to be a minimum.
This minimum setting counts for automatic scaled or not.
If we zoom in far enough then a single grid step can exceed a screen height and/or width.
At best there will be 1 Grid dot (or a single crossing pair of lines) but chances are that all is outside the visual viewport.

About visibility:
A Grid dot is the same thing in the same color in any zoom state.
Like Andrew said probably an optical illusion.


Regards,
CVH

[Chips&Chips]

I have played around with this some more today and I have confirmed that the Grid dots do remain the same size and color at different (all?) magnifications. At least until they do get too close together and then disappear. So yes, it probably was an optical illusion. It is a fact that there are fewer color sensors in the human eye than luminance (black and white) sensors. So a color with a similar luminance level can disappear when it becomes too small. And apparently this can work even when the luminance levels are fairly different. Here is the comparison photo pair I was going to say is evidence of the disappearance. But, when I zoomed in while putting them together in Paint, the dots were there and exactly the same color and size, in pixels. This is why we need settings for something like a grid.
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HereYouSeeThenAndHereYouDont.jpg (606.72 KiB) Viewed 1197 times

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I don't know if my observation can be verified with the jpeg image allowed by the BB software. But, as I said, the dots ARE still there in the second captured image.

I really don't like the black background. I am trying to develop a color scheme with the gray seen in my screen shots. I had an idea while trying to sleep last night. A Grid with full lines instead of dots and a color that is close to but slightly darker than the background color might work better. After some experimentation I found a custom gray color that seems to work. You can see this in the screen shot below.
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OKGridButMetaGridProblem.jpg (379.16 KiB) Viewed 1197 times

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But the Meta Grid is still problematic. I tried a number of colors and all of them seemed to be either the same as the Grid color or close enough to it to be invisible. This changed as I zoomed IN and OUT. I finally selected black because it is as far from the light gray background color I selected as possible. But even that was still troublesome. Then I zoomed out and saw the above. There seems to be some kind of periodic interaction between the Grid lines and Meta Grid lines. And the period appears to be different in the X and Y directions. This periodic variation in the Meta Grid was not visible when I was using dots instead of lines for the Grid. That's why I suspect an interaction between them.

Is this effect due to something in QCAD or is it my monitor? I can say that I have not seen it in any other CAD program that I have used in the past 30 years or so.

[CVH]

Is this effect due to something in QCAD or is it my monitor?

This Is most likely a screen effect and so far I can see the periodic nature is about 6'-8" in both X & Y speaking in 100% viewport terms.
It has to do with your screen DPI and if the horizontal or vertical line falls perfectly on a pixel or not.

Seeing a series of dots better than a few isolated dots has less to do with the capabilities of the eyes but more with the gray matter between the ears. Our eyes are fairly blind for details and also for the bigger picture but our mind is very capable in detecting/seeing patterns but also in inventing them. What we think what is our visual scope is actually a collage of hopefully more real parts than imaginary.
But tests have proved big time that we are fairly blind for things that we don't expect to be there and invent those we expect.

For me the dots in the lower example of HereYouSeeThenAndHereYouDont.jpg are perfectly visible.
I see the same wavy nature for the dots in the upper example as previewed on the Forum.
But when I open the image in a new browser tab at 100% the wavy nature is gone and all pixels have the same pronounced color.

Regards,
CVH