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Memory Management in PLS-CADD

The following discussion applies to the 32 bit edition of PLS-CADD only. The x64

edition is only limited by the amount of memory in your computer.

Several industry trends are contributing to a desire to load ever larger XYZ point filesinto PLS-CADD. The wide availability of reasonably priced high performance

LiDAR systems is one of them. Another is the use of PLS-CADD as a vegetation

management tool. In both cases the resulting files can be a challenge to work with.

This technical note will answer some commonly asked questions as well as give you

the background information necessary to make intelligent decisions about managing

this mass of data.

For the sake of efficiency PLS-CADD stores XYZ data sequentially in a single piece

of memory (an array). This provides for extremely fast operation, but imposes the

requirement that the system have a contiguous piece of memory that is large enoughto store all of your points. When Windows cannot supply this memory you run into

trouble.

One frequently asked question is: "how many points can I load"? The answer can be

arrived at via a simple formula:

Maximum # XYZ Points = (Largest available memory block) / (Size of XYZ Point)

Each XYZ point consumes 48 bytes (assuming there are no plan or profile comments

associated with it). The size of the largest contiguous block depends on which version

of Windows you are running as shown in the table below:

Theoretical XYZ Point Limits for the 32 bit Edition of PLS-CADD

Operating SystemService Pack

or Hotfix

Largest

Contiguous Block

(MB)

Total Available

Memory (MB)

Number of XYZ

Points (millions)

Windows 2000 SP4 1133 1981 23.6

Windows XP SP2 550 1969 11.4

Windows XPSP2 w/hotfix894472

809 1987 16.8

Windows XP SP3 800 1961 16.7

Windows VistaRTM and

SP11668 1935 34.7

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Windows Vista

x64 (also XP x64)

RTM and

SP12047 3999 42.6

Windows 7 RC 1570 1923 34.2

Note that these limits are taken from clean installs of Windows. It is possible thatdramatically less memory may be available and a correspondingly fewer number of

points may be loaded if the system has other software installed that is poorly behaved.

In other words, the limits given above are the best that you can hope to achieve.

The memory sizes listed are virtual memory, notphysical memory (RAM). In all cases,

we recommend you have at least 2GB of RAM installed in the system. The virtual

memoryis also known as the address space. The amount of address space that

Windows makes available to PLS-CADD is ultimately what governs how many points

you can load.

You will note that Windows XP SP2 took a large step backwards in terms of the

number of points which may be loaded. This is due to a bug in the original Windows

XP which was fixed in Service Pack 1 and subsequently reintroduced in Service Pack

2. Microsoft has ahotfixavailable which fixes this problem in SP2. One of the primary

benefits of Windows Vista is the increase in the number of points that may be loaded.

Memory

Preallocation

Consider twodifferent scenarios:

In the first PLS-

CADD asks

Windows for a

large piece of

memory and in the

other PLS-CADD

starts by asking for

a small piece of

memory and thenrepeatedly tries to

grow it until it is

the same size as the

large chunk. Due to a problem known as fragmentation, you can often get twice as

much memory in the former scenario as you could in the later. Restating this in a

PLS-CADD context, it is better to preallocate enough memory for the maximum

http://support.microsoft.com/kb/894472/http://support.microsoft.com/kb/894472/http://support.microsoft.com/kb/894472/

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number of XYZ points you could have than it is for PLS-CADD to repeatedly attempt

to grow your XYZ memory as you add points. TheF1/Survey and Terrain

Features/Preallocate memory for XYZ pointsfeature allows you to do just this. The

only caveat is that you should not preallocate any more memory than you need since

the memory reserved via preallocation is not available for other data such as raster or

vector attachments, PFL points, etc. The preallocation dialog is shown to the right.

How can I load more points?

What can you do if you have preallocated memory and still cannot load all of your

points? Here are a few suggestions:

1. If running on a 32 bit edition of Windows then upgrade to a 64 bit editionwhich will allow you to run the x64 edition of PLS-CADD. The x64 edition of

PLS-CADD can access an effectively unlimited amount of memory.

2. If running on Windows XP SP2 then apply thishotfixavailable fromMicrosoft. It fixes a bug in XP SP2 that prevents PLS-CADD from making full

use of the memory in your system.

3. Make sure that you do not have any attachments consuming memory when youtry to load XYZ points. InDrafting/Attachments/Attachment Managerhide all

of your raster images and detach any DXF files. Then save your project, exit

PLS-CADD, restart it and reopen the project.

4. Make sure that you have filtered data and not the raw LiDAR data directly fromthe flight. Filtering LiDAR data down to the set of points that are meaningful

for your design may allow you to avoid the entire problem of too many points.

Note that not every LiDAR vendor provides a filtered data set.

Just because you can load points doesn't necessarily mean you should. Each XYZ

point occupies memory that could otherwise be used for PFL points, raster and vector

attachments, etc. Further, many operations in PLS-CADD take a little more time with

each additional point you load. So, you want to have enough points to build an

accurate profile and detect all possible clearance violations, but no more than that.

Further Reading

Technical note:Working With Image Attachmentsin PLS-CADD can behelpful when managing memory.

Technical note: Transmission LineVegetation Managementin PLS-CADD. For hardware recommendations and additional information regarding x64

Editions of Windows read theFrequently Asked Questionsdocument.

http://support.microsoft.com/kb/894472/http://support.microsoft.com/kb/894472/http://support.microsoft.com/kb/894472/http://www.powline.com/products/photos.htmlhttp://www.powline.com/products/photos.htmlhttp://www.powline.com/products/photos.htmlhttp://www.powline.com/vegetation/dangertree.htmlhttp://www.powline.com/vegetation/dangertree.htmlhttp://www.powline.com/vegetation/dangertree.htmlhttp://www.powline.com/presales.pdfhttp://www.powline.com/presales.pdfhttp://www.powline.com/presales.pdfhttp://www.powline.com/vegetation/dangertree.htmlhttp://www.powline.com/products/photos.htmlhttp://support.microsoft.com/kb/894472/

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